Introduction

Building commissioning (Cx) is a professional practice that facilitates the planning, design, construction, installation and testing verification, documentation, and operation of facilities and systems to conform to the Owner's Project Requirements (OPR).

Building commissioning comprises specific phases and activities for both new construction and existing buildings. Whether commissioning new construction or existing buildings, the process includes many incremental activities, usually team-based functions that result in project-specific benefits and documentation.

Cx is the ONLY profession/entity, other than the owner, that is engaged throughout the process of design, construction, delivery, and optimizing performance of facilities. CxPs require a substantial amount of knowledge, skills and experience to be able to recognize, address, and even correct issues, and building/systems performance, through the eyes of every other team member and throughout the project.

This 8–page section of the Whole Building Design Guide (WBDG) presents overall commissioning process information, guidance, challenges, and resources. The first 4 pages are focused primarily on new construction commissioning, followed by pages 5 and 6 which outline the process and guidance for commissioning existing buildings whenever it occurs from initial occupancy through the life of the facility. Pages 7 and 8 describe challenges and further resources for owners, designers, contractors, commissioning providers (CxP), and consultants.

1. Building Commissioning: The Process
2. Determining Project Performance Requirements
3. Roles and Responsibilities in the Commissioning Process
4. Commissioning Documents: Process, Contents, and Acceptance
5. Existing Building Commissioning
6. Ongoing Commissioning
7. Commissioning Challenges and Emerging Issues
8. Additional Commissioning Resources

Building Commissioning requires a detailed and team oriented process.

Commissioning Benefits and Goals

The ultimate benefit of new facility and system commissioning is the documented performance of the facility and systems as it is transitioned into the long-term operations and maintenance function. Commissioning, used as a more forensic problem identification and solutions-based process, can be applied to an existing facility or system even if not initially commissioned, as described in Existing Building Commissioning.

Commissioning assists in the delivery of a project and helps to provide an efficient, safe and healthy facility; optimizes energy and water use; reduce operating costs; facilitate O&M staff orientation and training; and improve installed building systems documentation and operations. These functions can result in increased profitability in both facility and staff operations.

Commissioning benefits Owners through improved facility performance including higher quality workplace environments, and prevention of potential business losses. The cost of not commissioning is equal to the increased costs of correcting design and construction deficiencies later, plus the costs of inefficient operations. For example, in mission critical facilities, the cost of not commissioning can be measured by the cost of downtime and lack of appropriate facility use.

The primary goal of commissioning any project or system is to ensure that success for the project is clearly defined in the Owner's Project Requirements (OPR) and that the building and systems perform as intended to fulfill that mission. The commissioning process can be applied to an entire facility or to any specific system or assembly if new, upgraded or modified.

In addition to energy efficiency and overall performance drivers, another factor increasing demand for commissioning is the Owner's desire to obtain certification through building performance rating systems. These rating systems have been developed to improve the project planning, design, construction, and performance of energy and water efficiency, environmental conditions in buildings, verification, documentation, and operations practices. A building certified to these rating systems can include highly efficient gas, water, power and lighting systems, solar photovoltaics, and other energy and resource technologies. From an Owner's perspective, investment in these and other sophisticated building technologies must be accompanied by rigorous design and construction quality assurance and performance verification measurement, which are provided holistically through the commissioning process.

The principal goals of building commissioning are to:

1. Include the project requirements including the commissioning process in the OPR document.
2. Verify that the OPR requirements, including commissioning, are in the project design and construction documents for new projects.
3. Facilitate delivery of buildings and construction projects that meet the Owner's Project Requirements.
4. Prevent or eliminate problems in a cost-effective manner through proactive quality techniques.
5. Verify systems are installed and working as intended and benchmark that operation.
6. Provide and collect documentation and records on the design, construction, and testing to facilitate operations and maintenance of the facility.
7. Facilitate training functions and system operation documentation and Cx tools for O&M staff performance and implementation of ongoing Cx.
8. Lower overall first costs and life-cycle costs for the Owner.
9. Maintain facility performance for the building's entire life cycle.

Commissioning Definitions

Commissioning definitions vary slightly based on the project phases and the function of the Cx process in the specific sequence. The commissioning process can be implemented on an entire facility or on specific systems or assemblies as required by the Owner and project.

The following definitions depict commissioning as a holistic process that spans from pre-design planning to occupancy and operations at a minimum and should also include ongoing commissioning. As stated in ASHRAE Standard 202–2018: Commissioning Process for Buildings and Systems, the following definitions are provided:

Commissioning Process (Cx) — all, including New Construction (NCCx): a quality-focused process for enhancing the delivery of a project. The process focuses on verifying and documenting that all of the commissioned systems and assemblies are planned, designed, installed, tested, operated, and maintained to meet the OPR.

Existing-Building Cx (EBCx): a quality-focused process for attaining the Current Facility Requirements (CFR) of an existing facility and its systems and assemblies being commissioned. The process focuses on planning, investigating, implementing, verifying, and documenting that the facility and/or its systems and assemblies are operated and maintained to meet the CFR, with a program to maintain the enhancements for the remaining life of the facility. See Existing Building Cx.

• Retro-commissioning (RCx) is commissioning an existing building that has never been commissioned before.

• Recommissioning (ReCx) occurs when a building that has already been commissioned undergoes another commissioning process. The decision to recommission may be triggered by a change in building use or Ownership, the onset of operational problems, or some other need.

• Monitoring-Based Commissioning (MBCx) utilizes primarily monitored data (versus primarily manual tests and checks) originating from the Building Automation System (BAS) or other meters processed with special analysis tools, sometimes referred to as Energy Management and Information Systems (EMIS).

• System-Specific Commissioning is a tailored application focused on a small subset of targeted systems in a building, such as indoor environmental quality or chiller plant efficiency.

• Ongoing Commissioning (OCx) continuously gathers data about existing systems and building performance and continuously or regularly evaluates the data to ensure proper operation and to improve performance, usually dependent on hardware and software tracking tools and by a separate contractual arrangement after completion of NCCx or EBCx.

Description

The commissioning process ideally begins at project inception (predesign phase) and continues in phase-specific functions through facility and system operation. It is not a design or construction function, but it assists in and verifies that the results of these functions can produce a facility and systems that meets the requirements for performance. Depending upon the Owner's needs, these might include; functionality, efficiency, sustainability, environmental and health impacts, interior occupancy conditions, resilience, and others that will maximize facility and system profitability for the Owner and the occupants.

Commissioning for new construction typically involves a CxP for all phases until the building is occupied:

Phase 1 — Predesign. It is important to start the commissioning process in the pre-design phase. This early involvement by the CxP is critical for the timely and useful development of the Owner's Project Requirements (OPR), the subsequent design team Basis of Design (BOD), the Commissioning Plan, and the beginning of the Operations & Maintenance (O&M) Systems Manual. If these tasks are left until later in the process and "reverse engineered" to match the design, their usefulness as catalysts for dialog, cost and risk management, and quality tracking tools is lost.

Phase 2 — Design. During the design phase the project design and details are further developed and organized for the construction documents. These documents must be based on the design team's application of the OPR. If questions and variations to these requirements evolve during this phase, it may be necessary to update the OPR with the acceptance of the Owner or representative. The commissioning requirements are further developed during design including the selection of the systems to be commissioned and the specifications detailing the functions of commissioning and the contractor's and manufacturers responsibilities as part of the commissioning team. The commissioning plan is further developed during the design phase to reflect the design and performance requirements of the commissioned systems and the initial development of field observation, functional testing, and performance requirements, along with documentation formats for testing and reporting. During and at the conclusion of project design, the CxP reviews the construction documents to determine compliance to the OPR and inclusion of the commissioning requirements. The CxP design review is intended to verify compliance with the OPR and is not considered a PEER review. Any open issues should be responded to in writing from the designer for design completion.

Phase 3 — Construction. In the construction phase, the commissioning process transitions from planning to application and is active during the entire construction phase. During pre-construction, the commissioning schedules are developed and integrated into the construction schedules. The CxP reviews the submittals for the commissioned systems and further develops the field observation, testing, and functional and performance requirements and checklists in the commissioning plans. The commissioning team is assembled along with the general contractor and relevant sub-contractors, manufacturers, and suppliers and these Cx Team members participate in a project commissioning scoping meeting for training and coordination. Subsequent meetings are conducted as needed, including systems integration meetings for both building controls and other building alarm and operating systems. An issues and resolution log is created by the CxP to communicate problems, concerns, and questions during the project to the Cx team and Owner. This log is updated during the project and the final log is included in the commissioning report. Depending upon the project organization, normally the contractors complete the installation field observations and checklists as required by the commissioning plan. These completed checklists are reviewed by the CxP and any needed adjustments are performed on the Functional Performance Tests (FPT) and schedules. In coordination with the construction schedules, the FPTs are conducted by the contractors along with the CxP as a witness. Based on FPT results, a preliminary commissioning report is drafted and reviewed by the Owner and, if necessary, the local jurisdictions. Any necessary plans for deficiency correction and off-season testing are included.

Reviewing the construction documents and coordinating with the construction team to ensure proper implementation of the project and commissioning plan. Photo Credit: 33684514, Ndoeljindoel/Dreamstime.com

Phase 4 — Hand-Off/Occupancy. At project substantial completion and after conducting operations and maintenance training by the design team (if applicable), contractors, and suppliers, the Owner assumes operational responsibilities for the facility or project. The commissioning process is not complete until the off-season testing is completed and the systems manual is completed and transferred to the Owner. At that time, a final commissioning report is developed including the final issue logs with any open items as accepted by the Owner.

NEW CONSTRUCTION/SYSTEM COMMISSIONING DOCUMENTATION

The new construction commissioning process includes multiple activities performed in a specific sequence. As defined in ASHRAE Standard 202–2018, Commissioning Process for Buildings and Systems, these functions are required to provide a complete commissioning project.

1. Initiation: The Owner or Owner's representative initiates the commissioning process at the beginning of the project. The roles and responsibilities of the project and commissioning teams are determined. Procedures and contracts are prepared and executed.

2. Owner's Project Requirements: Next, the project requirements are determined and documented which include the building program, use, scope, and the requirements for performance, sustainability, resiliency, training, testing, commissioning, and documentation. The deliverable for this activity is the Owner's Project Requirements (OPR) document which is the guiding instruction for the project. The OPR is updated throughout the design and construction of the project. See Determining Project Performance Requirements for further information on assembling the OPR.

3. Commissioning Plan: The initial Commissioning Plan is developed by the CxP that identifies the commissioning scope, roles and responsibilities, communication procedures, and design and construction requirements for providing and integrating commissioning into the project. The Commissioning Plan is updated throughout the project with checklists, schedules, and documentation details. The Owner reviews and accepts this plan.

4. Basis of Design: The design team determines and documents the design approach to meet the Owner's Project Requirements resulting in the Basis of Design (BOD) document. The CxP reviews the Basis of Design for conformance to the OPR. The Owner reviews and accepts this document before design completion.

5. Specifications: During the design phase, the contractor commissioning requirements are determined for each system and included in the commissioning specifications for the construction documents package.

6. Design Review: In the design phase, the CxP reviews the design and documents for conformance to the OPR. This design review also provides details that facilitate the further development of the commissioning plans.

7. Submittal Review: The commissioning team reviews the materials and equipment submittals for conformance to the OPR and construction documents. The submittals also provide information and details to develop project and commissioning process checklists.

8. System Verification: As the project is constructed, the commissioning team observes and verifies the installation and performs or witnesses the equipment start up and initial testing. Checklists and reports are prepared as required by the commissioning plan.

9. Functional Performance Testing (FPT): Functional and performance testing is conducted according to the commissioning plan to verify performance compliance with the OPR and design documents.

10. Issues and Resolution Log: Issues and resolution of issues are identified and documented by the commissioning team in the Issues Log along with related documentation. This log is a communication device for questions and problems from all the commissioning team participants that need solutions to facilitate successful project completion.

11. Systems Manual: During the design and construction of the project, the design and construction and verification documents are assembled into the systems manual. This assembly is normally performed by the general contractor or PM. This assembly of documents provides the details and history of the design and construction of the building and information needed to properly operate and maintain the building. The commissioning reports are included in the final Systems Manual.

12. Training: Training of facility staff should be pervasive throughout the commissioning process. At the hand-off/turnover phase, formal training ensures that operations and maintenance staff understand the equipment and systems. Training activities ensure that operators understand the theory ("why") as well as how to control and maintain the systems ("how") to operate and use the building in accordance with the OPR and design capabilities, the building operational staff and users are trained on the installed equipment and systems.

13. Seasonal or Deferred Testing: Commissioning activities that were not performed due to climatic conditions or equipment availability before initial certificate of occupancy are conducted during post occupancy. The final testing results are included in the final commissioning report and systems manual.

14. Commissioning Report: At the time of granting a facility Certificate of Occupancy a preliminary commissioning report is prepared that shows the commissioning progress and equipment performance to date. At the completion of the project, the final commissioning report is assembled and provided to the Owner and others as required by the OPR and local jurisdiction requirements.

Careful observation is an essential component of the documentation process during commissioning.

COMMISSIONING PROCESS MANAGEMENT

The facility or project Owner, or representative, defines and manages the process and reviews the documents. During project planning, the Owner also defines the extent and requirements of the commissioning process along with the basic commissioning team functions and responsibilities. Those functions are further defined in Roles and Responsibilities in the Commissioning Process.

The CxP normally reports to the Owner or Owner's Representative. This relationship and the contract need to be established at the beginning of the project. The function of commissioning is to assure the Owner that they are receiving true and full value in the function and performance of the commissioned systems. Thus, the reporting relationship to the Owner reduces or eliminates the possibility of a conflict of interest by the CxP.

Application

Building and/or System Commissioning Initiation

Engaging the CxP at the beginning of the project allows the CxP to become familiar with programming documents and proceed immediately to the OPR workshop and the development of the whole building criteria that match the project needs including facility certifications such as LEED®, Green Globes, Living Building Challenge, WELL, among others, and jurisdictional requirements. The OPR should be developed during the pre-design phase. When developed first, the OPR can become a very useful tool to the Owner in selecting the correct design and construction team for the project. During the selection process of the design team, candidates' responses to the OPR when submitting their BOD provides tremendous insight into their understanding of the OPR.

When the Systems Manual requirements are also started at this early stage, the inclusion of O&M requirements is facilitated. The inclusion of O&M planning in the early phases is key to the long-term persistence of energy efficiency, equipment longevity, and whole building performance strategies built into the design.

Sample commissioning process as outlined in ASHRAE Guideline 0 that informs NIBS Guideline 3, the basis for LEED Enclosure Commissioning. Photo Credit: USGBC

Determining Project Performance Requirements

Every new project goes through pre-design and design phases that establish an Owner's needs, goals, scope, and design solutions for a proposed project. Proposed designs and constructed work can only be evaluated against objective criteria and measures that are embodied in a well-documented OPR. Project development is a learning process where building performance decisions are refined to successive levels of detail over the course of a project's life cycle. This may also include possible future programs such as solar, recycling, and new technology.

The project performance requirements are defined and assembled in the OPR document. The OPR is also the foundation document of successful Cx. It is critical in ensuring the commissioning process meets the Owner's goals. The OPR defines the cost expectations, performance goals, energy and operational benchmarks, high-level schedule dates, operational approaches, and success criteria for the project. Owner staffing plans for the facility should be clearly identified so any impact on the design of the facility systems is known. The OPR must be developed with significant Owner input and ultimate acceptance. The CxP typically assists the Owner in identifying the facility's requirements regarding such issues as energy efficiency, indoor environment, staff training, and operations and maintenance. An effective OPR incorporates input early in the project from the Owner, operations and maintenance staff, and end users of the building, and is updated throughout the project. A properly developed and updated OPR truly becomes the definition of success for a project.

Defining Cx Requirements for a Project

The commissioning process can be applied to an entire facility or project or to limited and specific equipment and assemblies. The specific commissioning application is defined in the OPR. Subsequently creating the Commissioning Plan (Cx Plan) will answer the questions and set the criteria for the commissioning process on the project.

Key project requirements and related commissioning activities include:

• Establish goals for project quality, efficiency, certifications, and functionality of commissioned systems
• Establish a commissioning scope
• Establish commissioning budgets
• Assign team members and responsibilities
• Establish commissioning plans
• Establish commissioning schedules
• Establish testing and field observation plans
• Develop commissioning specifications
• Determine scope and content of commissioning documentation and reports
• Define special testing needs
• Develop Systems Manual format and requirements
• Determine operational staff training needs
• Establish ongoing building commissioning (OCx) plans and requirements

The project requirements and the systems and assemblies selected for commissioning determine basic commissioning functions and requirements. Additionally, the Owner can require variations and options in the requirements, such as sampling or specific testing, when needed on a specific function or project.

Project Documentation, Records, and Acceptance

The purpose of commissioning documentation is to serve as the historical record of the "what, why and how to" of key delivery team decisions throughout the planning and delivery process. Commissioning documents the establishment of standards of performance for building systems and verifies that designed and constructed work meets those standards. Key commissioning deliverables supporting Document Compliance and Acceptance are included above in the New Construction/System Commissioning Documentation section, and in Commissioning Documents: Process, Contents, and Acceptance.

Additional Resources

See the Additional Commissioning Resources page for more information.

Introduction

The content of this section of the BEDG in the WBDG is intended solely as a means to create awareness of the relevant topics and concepts. The following information is general in nature, consequently the application of the concepts discussed in real world conditions will vary based on project specific performance considerations and site specific microclimate conditions unique to each project, geographic location and building façade.

In the creative process of building design, a great deal of consideration is given to the physical landscape of a development. Orientation of the future building's footprint, entrances, exits, glazing, interior spaces, etc., are prudently arranged and manipulated to create the most aesthetically pleasing, efficient, and economical plan for the desired use of form and function.

This task of optimizing the readily observable attributes of a plan to its physical landscape can be a daunting task further complicated by the analysis of additional unseen non-physical factors. These factors often include the analysis or impact of: radiant solar angles, sun shadows, noise, vibration, wind force, air quality, pedestrian level winds, snow loading, etc. These last non-physical examples have been traditionally grouped into an area called Environmental or more accurately Microclimate Studies.

The term "microclimate" is defined by Merriam-Webster.com as: "the essentially uniform local climate of a usually small site or habitat". The purpose of conducting these non-physical studies is traditionally two-fold; first to understand the existing microclimate of the site from the various points of study; and secondly to predict the negative impacts, interaction, and influence of the proposed building design on the microclimate and modify the design to mitigate negative impact.

Consequently, the effort to create an aesthetically pleasing, efficient, and economical plan can have immense challenges and trade-offs. That said, the purpose of this particular resource page is to bring awareness to one specific non-physical microclimate factor for consideration in design: winter weather or winter precipitation and its potential for hazardous conditions to people and property if not adequately anticipated. Further it is important to note that the occurrence of hazardous winter ice and snow formations cannot be eliminated and can only at best be reduced in frequency or severity.

Description

The Problem Condition

The following text has been created to raise awareness of an old topic that is of growing concern based on some current trends in the economy and industry at large. Buildings in cold climates have struggled throughout the ages with ice and snow formations that slide, fall, or get windblown from their roofs, ledges, and window sills, causing harm to people and damage to property below. Sliding snow from residential roofs has damaged cars, blocked exits, or even torn off gutters and flashing details. On larger commercial or public buildings the issues are largely the same; however, the potential for damage or injury grows as building surfaces are larger, buildings are taller, and the volume of pedestrian and vehicular traffic increases.

In densely populated urban centers, such as New York City, Boston, Chicago, Toronto, Denver, and Washington D.C.; where prominent tall buildings are constructed on small sites with pedestrian and vehicular traffic mere feet from their base, the tolerance for any potential hazard or interruption of building operations due to falling ice and snow, or the erection of yellow "caution tape" is significantly less. Furthermore, experience has shown that public and urban buildings in general have very little tolerance for shedding ice or snow, regardless of the magnitude of the potential hazard, if it is thought that the occurrence will be perceived as a danger, or damage a building's reputation for safety. This leads to the question: what size of ice or snow piece is acceptable to fall from a building, and how often is it acceptable for ice or snow to fall?

At this time in the advancement of the study topic, the answer to those questions has not been agreed upon within regulatory organizations. Therefore, the best course of action is to seek knowledge and expert advice where possible.

The Art and Science of Ice and Snow Assessment

The assessment of ice and snow focusses on the totality of the winter microclimate in an effort to predict and mitigate a variety of impacts that include:

• falling snow prediction
• falling ice or freezing rain accumulations
• sliding or movement of ice & snow
• melt water control & icicle formation
• wind drifted snow formations
• windblown snow infiltration
• freeze thaw damage
• obstructed views from skylights & clearstory windows

A damaged barrier on a small building ledge. Photo Credit: Northern Microclimate Inc.

Different from a snow loading study, the assessment of ice and snow has no prescribed or regulated criterion, standard or procedure by building codes to assist designers or engineers. Furthermore, an ice and snow assessment focusses on events that would interrupt building operations, services, or create a perceived or real hazard to people or property, compared to snow loading studies that are focused mainly on structural integrity and the potential for failure at a prescribed criterion target. For example: in general, a 50–year return period design criteria for snow loading on a roof surface is prescribed by building codes and is considered acceptable by the established authorities, in regard to the potential for failure of a roof structure. However, there is no corresponding requirement for the acceptability (return period or otherwise) of a falling icicle, windblown ice or snow piece, or sliding ice and snow accumulation from a roof or façade surface.

The current state of the industry is largely due to the complexity of the issues and corresponding number of variables that need to be considered. Furthermore, the analysis and computational models that would be required to predict the potential for building designs to experience hazardous ice and snow formations is beyond the current capabilities of economic study. Thus, the industry must rely on experience-based assessments conducted by consultants having a broad knowledge and experience in: microclimate analysis, building science, cold climate testing, and field investigation.

Characteristics of an Ice and Snow Assessment

The assessment of the potential for ice and snow hazard is generally accomplished through a design review process that considers historical meteorological statistics, local topography and surrounding buildings or structures in combination with the proposed building design. This allows for the frequency, directionality, and severity of winter storm conditions on the site specific microclimate to be evaluated and expressed in terms of potentially problematic conditions. For example: which building façade will be most affected by strong winter winds during snowfall; which direction will freezing rain storms impact the proposed building most frequently; and, where on the exterior of the building are hazardous ice and snow accumulations most likely to form.

If potentially problematic ice or snow formations are anticipated, design modifications can be recommended to reduce the frequency and severity of hazards. The recommendations are typically derived from past experience, including cold room test results and research of previous successful designs and/or field studies. If there is limited knowledge of the performance of a particular design feature, material or the affecting microclimate condition with the corresponding design feature or material, the refinement and validation of a mitigation concept can be recommended. This process is typically accomplished by conducting a full-scale physical test in a controlled cold room environmental chamber. This type of testing can be costly, however it is necessary to allow for the creation of the specific microclimate conditions required (or in question) to validate and refine a mitigation strategy or concept before it is implemented.

To demonstrate the varied aspects of ice and snow assessment, the following topics are discussed:

Building Geometries within their Microclimate

Once historical meteorological statistics have been reviewed and assessed in combination with the proposed building geometries, potentially negative influences of the building's performance within the local microclimate can be realized and improved upon. Examples of negative geometry and microclimate interactions can include:

• orientation of building form (long axis vs. short axis) or shape (curved, round or block forms, etc.)
• complex roof shapes that include slippery sloped surfaces, barrel vaults, roof steps, tower and podium interactions
• complex wall assemblies and sloped surfaces (double façades, trombe walls, complex curtain walls, etc.)
• locations of pedestrian access and/or exterior amenity areas such as courtyards, parking spaces, etc.

If these potential issues are identified and evaluated early in design, the risks of ice and snow hazard can be managed and improved upon, reducing their impact on cost and schedule, and resulting in more appealing aesthetics, as integrated mitigation designs can be investigated.

Envelope Design Considerations

Similarly, the ice and snow assessment can contribute to the decision process regarding envelope design. It is becoming evident that strategies to reduce energy consumption in buildings have a direct impact on the performance of the exterior building skin. Solar shading devices, high-performance wall assemblies and glazing products are generating significant energy savings in terms of long-term building heating and cooling requirements. However, these same strategies are having a negative influence on the accumulation and life span of ice and snow formations on façade surfaces. For example:

• the addition of exterior solar shading devices has significantly increased the exterior surface area available for ice and snow formation
• to obtain increased resistance to heat loss, exterior wall assemblies have in some cases increased in thickness thereby creating larger ledges and window sills
• high-performance glazing products have reduced heat loss thereby promoting increased volumes of ice and snow formations on glazing

Roof

The roof surface of a building can be a complex region, not only in terms of geometry or the presence of skylights, mechanical equipment, etc., but in terms of ice and snow design. Snow load considerations for ice and snow formations on roof surfaces govern the structural design of the roof and can significantly influence the entire structural design down to the footings of a building. However, as previously discussed, the prescribed snow load process is focused on long-term safety and durability of the structure to avoid catastrophic failure, and is therefore less focused on issues that can influence day to day building operations, public perception and the potential for falling, windblown or sliding snow hazards from a building.

Given these differences, there are two specific areas where the ice and snow assessment can contribute significantly to the structural design. These are sliding or moving snow on slippery sloped surfaces (metal or membrane roofs); and the integrity of the roof drainage path during the winter months.

The first topic has to do with ice and snow accumulations that in the correct meteorological conditions can slide or move, damaging roof projections, mechanical equipment, lighting protection, roof seams, parapet walls and in severe conditions the sliding ice and snow can slide completely from the roof surface damaging property or injuring people below. Circumstances that can lead to a sliding ice and snow scenario can be complex and are not well documented within the industry. This is where an assessment from an experienced ice and snow consultant can prove invaluable, if utilized during initial design rather than in a retrofit condition, which is often the case.

Sliding snow from a roof step on a smooth membrane roof. Photo Credit: Northern Microclimate Inc.

The second topic addresses a key assumption within snow load requirements, that all rain water and melt water from an ice or snow pack on a roof can readily leave the roof surface, therefore eliminating its contribution to the loading condition. However, in complex roof conditions or adverse meteorological conditions, a continuous warm (above freezing) path from source to drain for water flow may not exist. Gutters and roof drains have been known to freeze over with ice formations; alternatively, ice formations (an ice dam) at some location along the drainage path can block large roof areas from draining. Further complicating this issue is the application of heat trace to promote drainage. Often, the addition of heat trace is used to mitigate a potential blockage to the drainage path within gutters, downspouts and on roof surfaces. However, without specific knowledge of the ice and snow formations expected to be experienced, the application of heat trace can be ineffective or in some extreme cases cause problematic or hazardous ice formations. This again is where an assessment from an experienced ice and snow consultant can prove invaluable.

An ice and snow assessment can also help avoid potential issues: at clearstory windows and skylights (maintaining vision or sunlight as well as reducing leakage potential), at mechanical equipment and louvers (reducing snow ingestion or the drifting-in of equipment); and with the placement and size of screen walls and/or parapet walls.

Situating Entrances & Exits

The orientation, layout, or protection of building entrances and exits is also a task where the knowledge gained from an ice and snow assessment can be useful. Questions such as the following can be addressed in a timely and cost effective manner:

• Orientation to prominent winter winds
• Potential for snow infiltration
• Placement and detailing of canopies, wing-walls, wind screens, etc., as effective protection for building entrances and exits

Wind drifted snow cornice at entrance vestibule. Photo Credit: Northern Microclimate Inc.

Building Systems

The choice of building systems can also have an impact on the potential for hazardous ice and snow formations. Modern heating and ventilating systems, in conjunction with improved exterior wall performance, are reducing the reliance on perimeter heating, which in turn can increase the formation of ice and snow on exterior building elements. The overall impact can be a reduction in exterior skin temperature, which is small; however, the resultant increase in volume of ice or snow formation over an entire building skin can create problematic formations.

Planning for Occupancy

As the risk of hazardous ice and snow falling, sliding, or being windblown from a completed building cannot be eliminated under all possible winter conditions, it is therefore beneficial to provide guidelines to the building owner and future operations staff for the creation of operational protocols and winter maintenance plans with respect to ice and snow formations.

Emerging Issues

Energy Efficiency

In an effort to improve the overall energy performance of buildings, the profile of the exterior envelope or façade is changing. An increased use of solar shading devices or double façades has contributed to an increase in falling ice and snow incidents (these elements provide greater surface area for ice and snow to collect). Similarly, an overall increase in façade energy performance (i.e., increased insulation, reduced air leakage and better performing glazing) is contributing to larger ice and snow formations that can be windblown, slide, or fall from a building. Furthermore, the melt and re-freeze of accumulated precipitation on colder exterior surfaces contributes to dangerous icicles or ice sheets that can fall.

Design Trends

Building crowns, wing walls, large mullions, low or no parapets, green roofs, sloped walls and glazing (etc.); all contribute to falling ice and snow. Thus, a review of predicted winter performance of façade details during the design stages of a building is beneficial in identifying and reducing potential falling ice and snow risks.

Material Choices

Slippery roofs and sloped metal or glazed walls can allow ice and snow accumulations to slide and impact building components or areas below the roof or wall, posing a danger to people and property. Currently, there is little guidance available to address moving ice or snow on buildings. However, if the concern is identified during the design of a building and awareness brought to the potential for hazard, solutions can be sought.

Vegetative and cool roof construction techniques can each bring independent challenges to winter design.

The vegetative roof adds roughness and complex geometries potentially increasing the volume of snow collection on the roof surface, as well as increasing the potential for windblown snow transport on the roof surface, creating larger snow drifts in problematic locations. Furthermore, the build-up of soil and planting trays can create challenges with the melt water drainage path, possibly leading to ice formations at un-anticipated locations, creating localized loads. As well, freeze expansion damage to roof materials and flashing details can occur.

Cool roof construction, which is typically made up of increased insulation values combined with light colored roofing materials, has a significant impact on the rate of snow melt. The increased insulation reduces heat loss from the building's interior, while the light colored materials reduce solar absorbance. These two mechanisms can have varying impact on melt water production within an accumulated snow pack depending on the particular exterior weather conditions. However, in its simplest form, the melt out of snow will be slower, making the roof more susceptible to deeper snow, ice, and icicle formations, due to the potential for multiple snow storm events between melting periods. This in turn has implications to snow load assumptions, localized loading due to melt and re-freeze, and the formation of larger ice masses under deep snow formations that can promote sliding ice and snow and/or roof damage due to expansion forces.

New Technologies

Tall buildings can experience frequent wind driven icing at higher elevations. The ice collects in large volumes on parapets, cold walls, antennas, and other structural elements, and then falls. Incidents are rarely reported (publicly); however, they are frequent and increasing due to current design trends and the number of tall buildings. Experienced guidance is required to reduce potential of larger formations.

Relevant Codes and Standards

Building codes and standards have acknowledged the issues surrounding the potential for ice and snow movement on buildings, focusing on aspects of structural design. Some documents have gone further and acknowledge the potential for hazard and damage due to sliding ice and snow formations. However, the existence of procedures, instructions or guidelines that can be implemented to achieve a criteria or standard is not yet available.

Additional Resources

Publications

• Metal Roof Design for Cold Climates, Metal Construction Association.

Published Papers

• "Dam Ice Dam", ASHRAE Journal - Building Sciences 2010 by J. Lstiburek. June 2010.
• "Danger: Falling Snow" by D.A. Taylor. Published in Volume 35 Issue 1 of Canadian Architect, Reprinted in Construction Practice: Selected Applications in Construction Technology Section 2 (NRCC - 35475), 1990.
• "Minimizing the Adverse Effects of Snow and Ice on Roofs", Proceedings of the International Conference on Building Envelope Systems and Technologies (ICBEST-2001)  by J. Buska and W. Tobiasson. Ottawa, Canada: 2001.
• "Sliding Snow and Ice on Buildings: a balance of risk cost and aesthetics", Proceedings of Snow Engineering V by C.J. Williams; M. Carter; F. Hochstenbach and T. Lovlin. London, England: Published 2004.
• "Sliding Snow from Sloped Roofs: Its Prediction, Potential Hazard and Mitigation", Proceedings of Snow Engineering VI by N. Isyumov. Whistler, British Columbia, Canada: 2008.
• "Sliding Snow on Sloping Roofs", Canadian Building Digest CBD-228 by D.A. Taylor. Institute for Research in Construction, November 1983.
• Snow and freezing water on roofs, Cold Climate HVAC by A. Nielsen and J. Claesson. Greenland Sisimiut: 2009.
• "Snow, ice and icicles on roofs - physics and risks", 7th Nordic Symposium in Building Physics by A. Nielsen. Reykjavík, Iceland: 2005.

Articles

• "Beware of Falling Ice and Snow: A winter perspective on building design", Construction Canada, Vol. 54, No. 1. by Mike Carter, C.E.T. and Roman Stangl, C.E.T., January 2012.
• "Winter Weather Considerations: Avoiding Ice and Snow Damage During the Winter Months"  by William Meyers. Architectural West, March/April 2010.

Websites

• Snow Engineering—Snow and Ice Studies, Alan G. Davenport Wind Engineering Group, Boundary Layer Wind Tunnel Laboratory, University of Western Ontario
• U.S. Army Cold Regions Research and Engineering Laboratory Facilities and Products

Introduction

The innovative design of building enclosures relies less on successful past precedents than the application of building science. This is not because there is little to be learned from existing buildings, but is due to the changes in materials and methods that result from building technology innovation. Combined with growing expectations for high performance, building enclosure design is now required to satisfy a large number of performance parameters that were not given a great deal of consideration in the past. Building enclosures were always expected to be durable and provide a degree of environmental separation, but now they must address issues like energy efficiency, daylighting, indoor air quality, fire safety, thermal comfort, and carbon footprint. There is now a need to explicitly ensure these performance objectives are fully satisfied at the design stage.

Performance: the level of service provided by a building material, component or system, in relation to an intended, or expected, threshold or quality.

Performance-based design is not a new idea and in fields like structural engineering, limit states design has been deployed to reliably achieve appropriate levels of performance. There remain a number of challenges to overcome before a similar approach is available for building enclosure design. Until such time, the information that follows is intended to provide a practical framework for applying building science principles and strategies to the design of well performing building enclosures.

Before continuing with this Resource Page, it is highly recommended to review a summary of building science Vocabularyⁱ in order to be consistent with the terminology used throughout the building science series of WBDG Resource Pages.

For those interested in knowledge enrichment, access Historical Development of the Building Enclosure to understand how ideas and technology have evolved.ⁱⁱ

Description

Principles of Enclosure Design

The requirements for wall performance were outlined some half a century ago (Hutcheon 1963)ⁱⁱⁱ, and are applicable to all enclosure systems and components. The major considerations were identified as:

1. Strength and rigidity
2. Control of heat flow
3. Control of air flow
4. Control of water vapor flow
5. Control of liquid water movement
6. Stability and durability of materials
7. Fire
8. Aesthetic considerations
9. Cost

Since Hutcheon's time, additional objectives have been adopted, such as consideration of the environmental impacts associated with building methods and materials, and the need to provide safe and secure buildings. The objectives or requirements for acceptable wall performance were implicit within traditional methods and materials of construction. With the advent of modern building science, these objectives became more explicit in response to technological innovation. Table 1 summarizes contemporary performance requirements and their corresponding assessment parameters.

Table 1. Performance requirements for building enclosures and their corresponding assessment parameters.

Separator Versus Moderator

A critical principle in building science involves the difference between environmental separation versus moderation. For example, the control of fire and smoke movement is understood to be a strategy that attempts to completely separate smoke and fire from the indoor environment. The strategy employs a fire-rated assembly that fully controls the leakage of smoke by virtue of its airtight construction and in some cases, the control of air pressures between compartmentalized spaces.

Moderation involves a strategy where the severity of the difference between the indoor and outdoor environments (or two adjacent indoor environments) is moderated within a tolerable threshold. For example, the control of heat transfer does not seek to reduce the rate of heat transfer to zero, rather to a level that satisfies requirements for comfort, energy efficiency and the control of condensation/wetting. Table 2 summarizes key control strategies for the design of building enclosures, most of which involve a moderation strategy rather than a separator or 'perfect barrier' strategy.

Table 2. Fundamental strategies for the control of heat, air, moisture and solar radiation in the design of building enclosures.

A review of the physical phenomena and corresponding control strategies indicates the control of moisture migration is by far the most important control function to be addressed by the designer. Moisture related problems in buildings are common and broadly vary in types and consequences. A brief listing of moisture related problems illustrates this point: frost heaving, adfreezing, water leakage, wood rot, mold growth, spalling, efflorescence, corrosion, and deterioration and staining of finishes. Consequences range from structural failure to cosmetic flaws, and in some cases the health of the occupants can be adversely affected as in the case of mold growth causing allergic and respiratory problems.

The list of the harmful effects of water in building materials and assemblies is indeed a long one. In many instances the water by itself is not harmful, and only when combined with other phenomena does it cause rapid deterioration. On the other hand, the other phenomena involved will not cause deterioration in the absence of water. It follows then that if water can be controlled a building can be made more durable and the maintenance and repair costs reduced. If this could be achieved only by the use of very expensive materials and construction it could be argued that it is better to let the building deteriorate and to replace the damaged portion from time to time. In fact, however, durable construction can be achieved with relatively inexpensive materials and designs, provided that the designer understands the behavior of water in its various forms and applies the necessary controls to prevent it from accumulating in harmful quantities.^iv

Addressing the control of moisture in building enclosure design generally takes precedence over other control measures simply because so many of the requirements for the control of heat transfer, air leakage and solar radiation are satisfied when all forms of moisture management have been carefully considered.

A number of related pages are dedicated to explaining these various control strategies in depth:

• Air Barrier Systems in Buildings
• Moisture Management

For the purpose of applying building science effectively, it is important to appreciate the building enclosure is the primary environmental separator/moderator. It performs a passive role, unlike mechanical and electrical systems that actively supplement the amount of heat, air, moisture and daylight the enclosure is unable to provide. When all active systems fail, the building enclosure is the last line of defense between the indoors and the outdoors. High-performance building enclosures provide passive survivability during extreme weather phenomena and natural disasters, and safely shelter their inhabitants. The following section outlines a number of critical relationships and factors involved in the design of building enclosures.

Design, Materials, Workmanship

In order to appreciate the approaches involved in building enclosure system design strategies, it is important to understand several key relationships that impact performance.

1. Workmanship and materials are imperfect. If it is likely for a set of working drawings and specifications to contain errors and omissions, then it is almost a certainty that the translation of these instructions to contractors and their trades will be imperfect. Inaccuracy and inconsistency of workmanship and materials, in conjunction with variable weather conditions, result in buildings that only approximately fulfill their design intent.

2. Management approaches with respect to physical phenomena affecting the building enclosure system are shown through experience to be superior to barrier approaches. Not only do they provide redundancy of critical control functions, but they are more forgiving to construct, since tolerances are greater than those required by a barrier approach.

3. Enclosures must adequately control moisture migration, heat transfer, air leakage and solar radiation. Experience indicates that when the requirements for the control of moisture migration have been satisfied, the other control requirements are either simultaneously satisfied, or more easily satisfied than if moisture migration is not addressed at the outset.

In practical terms, these relationships guide designers to assume flawed construction that must be compensated with redundant control measures focused on moisture management. For experienced designers these assumptions are almost axiomatic.

Physical Phenomena

Environmental conditions, both internal and external, establish the physical phenomena that impact the performance of the building enclosure. In order to be durable and provide adequate moderation of the environment, the building enclosure must be designed to provide a threshold of control over, or resistance to, these phenomena.

Figure 1. Imperfect building enclosures must manage all imposed internal and external environmental phenomena.

Intensity, Duration, and Frequency

All physical phenomena share intensity, duration and frequency as defining characteristics. Events such as earthquakes, tornadoes, hurricanes, and to some extent floods, are typically high intensity phenomena of short duration and low frequency. In most climate zones, vapor diffusion, heat transfer, and air leakage are normally low intensity phenomena of relatively long duration and seasonal frequency. Both types of phenomena have accounted for considerable damage to buildings, however, the strategies for dealing with each varies not only in terms of the actual control measures, but mainly according to the associated risks and consequences of failure.

Risk and Consequences

Risk of failure involves the probability of a specified level of performance proving inadequate to resist an imposed physical phenomenon or phenomena. The likelihood of failure must be reconciled with the consequences of failure in terms of safety, health, functionality, economy, and aesthetics. Minimum levels of adequacy for health and safety in buildings have been established through codes and standards, and guide the designer in these vital aspects of building performance. However, the risks and consequences of failure for a building requirement such as structural integrity are much better understood than for moisture protection. For this reason, many building enclosure design strategies are based less on probability and analytical models, and more on precedent, heuristics, and common sense. This does not suggest that analysis is completely abandoned, but instead acknowledges that the results are often only accurate to within one order of magnitude. Numerical data must be interpreted qualitatively, requiring significant experience and judgment on the part of the designer.

Durability and Redundancy

Durability is a key consideration in effective enclosure design and this requires that a level of redundancy be provided in terms of critical control functions for moisture, heat, air leakage, and solar radiation. [Resilience is a concept related to durability that applies to the design, construction, and operation of buildings and infrastructure that are resistant to natural and man-made disasters.^v]

Redundancy—An enclosure with more than one 'line of defense' against imposed phenomena may be redundant with respect to one or more critical control functions. The degree of redundancy may range from: (i) resistance to each imposed phenomenon is distributed across all materials in the assembly (fully redundant); to (ii) resistance to each imposed phenomenon correspondingly addressed by individual materials within the assembly (non-redundant, hence each material represents a 'perfect barrier'). To be cost-effective and practical, redundancy is not simply doubling up on every control layer, or only selecting materials that address all of the control functions simultaneously. Control layers may be selected so as to perform more than one control function, or to significantly contribute to enhancing the performance of one or more control layers.

Multi-Functionality—A material may be uni-functional, such as a structural element, or it may address more than one required control function resisting imposed physical phenomena. Multi-functionality may be described as either: (i) single material addresses all enclosure control functions; or (ii) material primarily addresses one control function (first line of defense) and contributes to another control function(s), (second line of defense). For example, exterior insulating sheathing can act as a thermal control layer while contributing to air leakage and rain penetration control. If it is a vapor resistant material, such as extruded polystyrene, the exterior insulating sheathing can also resist vapor diffusion.

Contribution—A material may improve or enhance the performance of another material or assembly of materials without displaying multi-functionality or explicitly adding to redundancy. For example, an air barrier membrane may reduce air movement through an air-permeable insulation material, improving its thermal effectiveness but not contributing to the nominal thermal resistance of the assembly.

High-performance building enclosures provide high levels of resistance to imposed phenomena by intelligently arranging materials that are multifunctional with respect to critical control functions and contribute to the enhanced performance of one or more materials comprising the assembly.

Continuity

The continuity of critical control functions is among the most significant considerations when detailing building enclosures. Air and water leaks along with thermal bridges not only compromise performance but often lead to severe degradation of the building enclosure. In extreme cases, problems such as mold arise from a failure to maintain continuity of critical control functions. There are four Resource Pages that address building enclosure transitions to maintain continuity: Integrating the Building Enclosure; Wall to Roof Transitions; Wall to Window Transitions; and Wall to Foundation Transitions. For the purposes of enclosure design principles and strategies, it is extremely important to observe the need to achieve continuity of critical control functions, especially at transitions between enclosure assemblies.

Buildability and Economy

Lines on working drawings are straight, and the dimensions are precise, but in the field the building artifact is always an approximation, sometimes too crude an approximation to perform adequately. How does this come about?

Contractors and their trades are highly constrained by time and budget on virtually all construction projects. They are generally not inclined to spend more effort on construction than it is economically worth. If the successful (usually lowest) bidder on a construction project discovers that an assembly or detail is too expensive to execute properly, then ad hoc modifications (a.k.a. cutting corners) may be implemented by workers intent on meeting productivity quotas.

In some cases, the skill levels of the trades may be too low for the work they have been awarded. In other cases, the knowledge and experience of those performing quality assurance and supervision are simply not up to par. When none of the above factors come into play, other problems such as substandard materials or bad weather affect the quality of the finished product. Unforeseen site conditions, usually involving soils and groundwater, may compound the situation further, along with human factors such as labor disputes (strikes).

For these reasons, practical considerations in design should not be underestimated. Forgiving building systems that accept the reality of imperfect materials, workmanship, site conditions, and human factors are truly elegant and sustainable design solutions. Details whose proper execution demands the most efficient and least expensive methods are the real masterpieces of building enclosure design. This approach is certainly preferable to being 50% over budget on a project with a leaky roof, especially from the perspective of the building owner.

The economy of a building enclosure, in particular its initial capital cost, is largely determined by buildability, which also impacts its life-cycle economy if assembly of the enclosure exceeds the capability of the work force. Bad details lead to bad workmanship and ultimately poor performance.

Building Enclosure System Integration

The architectural design of building enclosures, foundations, walls, roofs, windows, and doors demands functional integration and aesthetic orchestration. Assuming that each of these assemblies and components has been individually resolved, it must be recognized that a second order of design/assessment is subsequently required. This ensures that the major assemblies and components are compatible, both mechanically at their connections and intersections, and in terms of their collective contribution towards the management of critical control functions. This iterative process from architectural concept, through physics, materials, and components, and back to the building as a system is a cornerstone of modern building science and its contribution to architectural design practice. Keeping these principles and key relationships in mind, the next section examines the critical physical phenomena that need to be considered in the design of effective building enclosures.

Climate, Exposure, Occupancy, and Building Energy Profile

Designing an effective building enclosure must properly consider the following factors:

1. Climatic zone where the building is located
2. Annual exposure to precipitation
3. Intended use or occupancy of the building (interior climate class), and
4. Building energy profile (skin-load versus internal-load dominated).

Based on these factors, it is possible to design building enclosures that adequately address all of the imposed physical phenomena while delivery high performance.

Climate Zones (Hygrothermal Region)

ASHRAE has defined 8 basic climate zones, some with variations, as listed in Table 3.

Table 3. ASHRAE climate zone definitions used for the design of hygrothermal control functions in building enclosures.

Climate zones influence the selection and arrangement of hygrothermal control layers in a building enclosure. The appropriate levels of thermal resistance may also be derived from the zone thermal criteria. Figure 2 depicts the hygrothermal climate zones of North America.

Figure 2. The selection and arrangement of heat and moisture (hygrothermal) control layers is based on climate zones. North America has all 8 climate zones and this broad range of climates explains why enclosures that are effective in one climate zone fail to perform properly in other climate zones.

Another way to understand climate zones is in terms of wetting and drying potential. All of the humid and marine climate zone variations in Table 3 have a high wetting potential and a low drying potential. This means that if the building enclosure experiences wetting due to moisture migration from either the exterior and/or interior, it will likely not dry out fully and be susceptible to mold and decay. Mixed, warm, hot, and very hot climate zones that are humid or marine will predominantly experience vapor migration across the building enclosure from the exterior toward the interior, while the cool, cold, very cold and subarctic zones will experience vapor flow from the interior to the exterior. The practical implications of these phenomena are presented in Understanding Air and Vapor Control Layers.

Precipitation Exposure

The annual quantity of precipitation is an indicator of the wetting potential of a particular geographic location, and also informs the selection of an appropriate cladding system that can adequately manage the amount of rainfall exposure.

Figure 3. Annual precipitation exposure is a critical factor in the selection of a suitable cladding system that can provide adequate moisture protection.

Indoor Climate Class

Table 4. Indoor climate classes based on a qualitative index advanced by Lstiburek 2002.^vi

The building enclosure must also withstand environmental loads based on the interior building conditions. Table 4 outlines indoor climate classes based on temperature, vapor, and air pressure regimes. It should not be confused with ISO Standard 13788 characterization of indoor climate classes. Instead, it should be employed as a guide to the level of moderation or separation that must be achieved by the control layers. For example, a warehouse for storing non-perishable goods may be temperature moderated by a heating system set to prevent freezing but with no intentional means of controlling humidity or air leakage. As such, there will not be large gradients across the building enclosure and only minimal control layers will be required. On the other hand, in a facility where temperature, vapor, and air pressure must all be carefully controlled, such as a pharmaceutical laboratory, it will be essential to provide high quality control layers to provide adequate resistance across the full range of differential gradients that must be maintained within a relatively narrow tolerance.

It is important to note that the higher the climate class, the more environmental stress will be placed on the control layers. Not only do the materials comprising the control layers have to be properly specified, but their detailing to ensure continuity must also be carefully devised. In the past, building designers relied on the power of HVAC systems to manage indoor environmental conditions, but since the time of the first energy crisis in the early 1970s, there has been a steady move away from active systems of environmental control in favor of passive systems, primarily the building enclosure.

Building Energy Profile

From an energy efficiency and thermal comfort perspective, buildings are often classified according to the primary drivers for space conditioning loads. This translates into two major profiles of buildings: skin-load dominated; and internal load dominated. The design of the building enclosure must account for these characteristics to provide energy efficient operation and deliver thermal and visual comfort to the occupants.

Skin-Load Dominated Buildings

A skin-load dominated building has the largest proportion of space conditioning energy loads determined by the building enclosure. This type of building is characterized by a relatively low occupant density where internal heat generation is minimal (e.g., housing), and natural ventilation and daylighting may be easily accomplished. They are also located in a climate that is either cold or colder, or hot or hotter. Mild climates do not exert a significant temperature differential over a sufficient duration to render buildings skin-load dominated. This building type relies on high-performance windows set in a thermally efficient enclosure with minimal air leakage and thermal bridging. In general, skin-load dominated buildings benefit from passive solar heating strategies in cold climates and solar shading and natural ventilation strategies in hot climates. Typical skin-load dominated buildings include houses, apartment buildings, small commercial and institutional buildings.

Figure 4. Skin-load dominated buildings benefit the most from high-performance building enclosures, and can take the best advantage of passive control strategies.

Internal-Load Dominated Buildings

Buildings that have high occupant densities and high internal gains from lighting and/or equipment are considered internal-load dominated buildings. Sometimes these are also referred to as a core-load dominated building. Regardless of climate type, the internal heat generation puts high demands on ventilation and cooling that are further driven by solar gains. For this building type, efficient means of rejecting excess heat generation translate into building enclosures that are typically less thermally efficient than effective at reducing solar gains by deploying shading devices and selecting appropriate optical properties of glazing. Different fenestration and shading strategies can also be deployed corresponding to the solar orientation of each face of the facade. Office towers and large retail facilities like shopping malls are notable examples of internal-load dominated buildings. Integration of the building enclosure with the HVAC systems is critical for achieving high performance in these types of buildings.

Figure 5. The energy performance of internal-load dominated buildings is strongly influenced by the window-to-wall ratio, effective U-value and solar heat gain coefficient of the glazing, and the airtightness of the building enclosure. Heat recovery for ventilation air and lighting system efficiency are the two most critical considerations for active building systems in these types of buildings.

There are also hybrid building types based on their changing occupancy. Schools are an example of buildings that are internal-load dominated when the classes are full during the day, and skin-load dominated on evenings and weekends when they are unoccupied.

It is important to appreciate that the hygrothermal design of a building enclosure to properly manage moisture, heat, and air flow is a function of the climate zone, precipitation exposure and indoor climate class. The building energy profile type is taken into consideration for the optimal levels of thermal insulation and selecting strategies for daylighting, passive solar heating, shading devices and passive cooling (natural ventilation).

Building Enclosure Design Strategies

Design strategies for building enclosures are a relatively recent opportunity for building designers. In the past, locally available materials and successful past precedents guided a highly traditional building industry where certain types of performance problems, (i.e., energy efficiency, thermal comfort, etc.), were considered acceptable. Today, a multitude of performance requirements must be satisfied amid a marketplace of innovative materials, components, and systems the designer is responsible to fully integrate, and the constructor must properly deliver. Picking a suitable generic building enclosure typology is an important first step.

Building Enclosure Typologies

The discussion that follows is focused on exterior walls recognizing that many of the considerations also apply to roofs and below-grade assemblies. It is interesting to note from Figure 6. that after thousands of years of building construction by humans, only a handful of building enclosure typologies have emerged. Most of these evolved by trial and error with some recent innovations arising from the application of building science principles, especially as it relates to rain penetration control.^vii

Figure 6. Schematic representations of basic building wall enclosure typologies.

Storage and Drying

Traditional masonry buildings relied on the storage and drying strategy for the management of moisture on a seasonal basis. The monolithic masonry façade was not only part of a load-bearing system, but also a hygric buffer with a capacity to store large quantities of water during wet periods, which are then released during dry periods. As long as the hygric buffer capacity was sufficient to store moisture accumulations, and the flow of moisture was not impeded at either the interior or exterior of the wall, this enclosure system would render good service. Some drawbacks of this strategy are the large quantities of materials and labor needed to erect the enclosure, the poor thermal efficiency due to a lack of insulation, and the absence of an air barrier system. Durability and moisture management are achieved at the expense of energy and thermal comfort. It is important to note that by abandoning this approach in favor of high performance, critical considerations have increased while margins of error have decreased.^viii

Perfect Barrier

Modern building science experience has demonstrated that perfect barrier or "face seal" strategies for building enclosures do not have a high likelihood of acceptable performance, except for highly arid climate zones. The imperfect nature of materials and workmanship results in a high probability the perfect barrier will have discontinuities, either at the time of construction / assembly and/or after exposure to the elements. Maintaining a perfect barrier is a costly and perpetual proposition. Perfect barrier or face seal systems do not have any redundancy of critical control functions, have no provisions for draining unintentional water penetration, and should therefore be avoided in high-performance building design. Perfect barriers or face seal systems rely on tightly sealed joints using caulking and/or gaskets to resist water and air leakage. This approach has been applied to components such as windows and doors that are manufactured under controlled conditions in factories. The joint between the component (window) and the opening in the enclosure is also highly dependent on workmanship and material durability.

Dynamic Buffer Zone

The dynamic buffer zone is a strategy employed in the preservation of historic buildings where the exterior facade cannot be altered, but typically cooling is being provided through a modernized HVAC system. This is exclusively an enclosure retrofit strategy intended to create a buffer zone inboard of the existing facade, which continues to reside in its original hygrothermal environment.

Graduated Mediators

The most notable contemporary example of a graduated mediator is the double-skin facade (DSF), but there are many historical precedents where a system of overhangs, screens, and louvers manipulated insulation, shading, and natural ventilation to enhance environmental control. This strategy is usually associated with mild climates where the potential passive contribution of the enclosure is significant. In more extreme climates, a single enclosure assembly is generally preferred as this enables multiple lines of defense (in effect a compressed graduated mediator) to be incorporated cost-effectively into a more conventional building enclosure.

Pressure Moderated Drainscreens

This term refers to a family of enclosure typologies that deploy a cladding that has a vertical airspace behind it that is drained to the exterior. A drainage plane, usually in the form of a sheathing paper, prevents bulk water from penetrating past the air space. Pressure moderated drainscreens, also known as cavity walls in masonry construction, may be vented or unvented, with the latter approach being recommended for water absorptive cladding materials such as wood and brick. The fundamental principle behind this strategy is to make it much easier for the water to get out than to get in the assembly. Moisture management for this type of enclosure relies on the 3-Ds: deflection, drainage, and drying. This strategy can be deployed in a wide variety of enclosure types including, wood/metal/vinyl siding, brick/masonry, precast concrete, and EIFS^ix. Typically, this enclosure strategy is suitable for low and mid-rise buildings. For high-rise buildings, a pressure-equalized rain screen strategy is recommended.

Pressure-Equalized Rain Screens

Pressure equalized rain screens are an invention of modern building science. Drained cavities that proved effective in low-rise buildings evidenced air and water leakage on high-rise buildings due to extreme wind speeds. The concept behind pressure equalized rain screens is to create air pressure chambers behind the cladding by compartmentalizing the air space with baffles. Wind pressures would be neutralized in these pressure equalization compartments, thus eliminating a driving force for rain penetration. Considerable research has shown this approach to be effective even when it is not perfectly achieved in practice.^x

Pressure equalized rain screen principles can be applied to a wide variety of cladding system including curtain walls. Best practices for the design and detailing of pressure-equalized rain screens have been developed to assist designers.^ix

Figure 7. Pressure equalized rain screens are idealized drainscreens that manage air pressure differences through compartmentalization of the air space behind the cladding. In reality, the pressure equalization is not perfectly achieved, but rain penetration can still be adequately controlled with this strategy as long as a continuous, structural air barrier is provided.

Drainscreens, Rain Screens and Enclosure Fundamentals

There remains a great deal of confusion about drained enclosure assemblies, due in part by the nomenclature that has been used: cavity wall, rain screen, drainscreen, pressure-equalized, pressure-modulated, pressure-moderated, and rear ventilated are just some of the terms that may be found in publications. It is helpful to shed light on this fuzzy situation.

Figure 8. Enclosure assemblies that conform to building science principles of performance consist of three primary elements from inside out: the structure; control layers (heat, air, moisture, solar); and the cladding.

If it is generally acknowledged that the mass wall and the perfect barrier approach do not constitute feasible alternatives for high-performance buildings, then the only enclosures worth considering provide drainage and some degree of air pressure moderation. While the graduated mediator may be engineered to deliver a high level of control it is not off-the-shelf technology readily available in most building markets. The pressure moderated drainscreen, in a variety of forms and proprietary systems, is suitable for low to mid-rise buildings, and the pressure equalized rain screen is well suited to high-rise buildings. Regardless of the approach selected, building scientist Joseph Lstiburek has demonstrated it must conform to the schematic arrangement of enclosure elements depicted in Figure 8.^xii

Important Note: The ordering of cladding, control layers, and structure do not change regardless of climate type. Cladding and control layers always reside outboard of the structure, which is held at a relatively constant temperature to minimize thermal stresses, and thereby maintain dimensional stability.

Lstiburek has demonstrated this arrangement is equally applicable to roofs and floor slabs, suggesting there are not nearly as many feasible enclosure typologies as might be portrayed by the wide variety of building materials, components, and assemblies available in the construction marketplace. The corollary to this observation is that only a subset of available building enclosure technologies is suitable to a particular combination of climate, exposure, indoor climate class, and building energy profile. Contrary to popular misconceptions, there are only a handful of successful building enclosure design strategies with proven past performance available to designers. ^xiii It is therefore advisable to ensure the proposed design solution conforms with a feasible generic building enclosure strategy that observes these fundamental building science principles.

Additional Resources

Publications

• Building Envelope by Canada Mortgage and Housing Corporation.
• Building Science for a Cold Climate by N.B. Hutcheon and G.P. Handegord. Institute for Research in Construction, 1983.
• Building Science for Building Enclosures by John Straube and Eric Burnett. Building Science Press, December 2005.
• Designing the Exterior Wall: An Architectural Guide to the Vertical Envelope by Linda Brock. John Wiley and Sons Inc., 2005.
• Evolution of Wall Design for Controlling Rain Penetration  by G.A. Chown, W.C. Brown, and G.F. Poirier. Construction Technology Update No. 9, December 1997.

References

i. BSI-024: Vocabulary by Lstiburek, Joseph. Building Science Insight #024, September 9, 2009.

ii. BSD-007: Historical Development of the Building Enclosure by Straube, John. Building Science Digest #007, October 24, 2006.

iii. CBD-48: Requirements for Exterior Walls by Hutcheon, N.B. Canadian Building Digest #48, December 1963.

iv. Water and Building Materials by Latta, J.K. Canadian Building Digest #30, National Research Council Canada, June 1962.

v. Secure / Safe. WBDG Secure / Safe Committee.

vi. Moisture Control For Buildings by Lstiburek, Joseph, 2002. ASHRAE Journal, February 2002, pp. 36-41.

vii. Rain Penetration and Its Control by Garden, G.K. CBD-40. April 1963.

viii. BSI-039: Five Things by Lstiburek, Joseph. Building Science Insight #039, April 20, 2010.

ix. BSI-038: Mind the Gap, Eh! By Lstiburek, Joseph. Building Science Insight #38, February 22, 2010.

x. Facts and Fictions of Rain-Screen Walls by Rousseau, M.Z. Construction Practice: Selected Applications in Construction Technology, NRCC 35475, 1993.

xi. The Rain Screen Wall System by Canada Mortgage and Housing Corporation, Ottawa.

xii. BSI-001: The Perfect Wall by Lstiburek, Joseph. Building Insight #001, May 20, 2008.

xiii. BSD-018: The Building Enclosure by Straube, John. Building Science Digest #018, August 1, 2006.

The National Institute of Building Sciences (NIBS) under guidance from the past Federal Envelope Advisory Committee developed this comprehensive guide for exterior envelope design and construction for institutional / office buildings. Any edits, revisions, updates or interest in adding new information should be directed to the Building Enclosure Technology & Environment Council (BETEC) through the 'Comment' link on this page.

Introduction

Below Grade Systems

• Foundation Walls
• Floor Slabs
• Plaza Decks

Wall Systems

• Cast-In-Place Concrete
• Exterior Insulation and Finish System (EIFS)
• Masonry
• Panelized Metal
• Precast Concrete
• Thin Stone

Fenestration Systems

• Glazing
• Windows
• Curtain Walls
• Sloped Glazing
• Exterior Doors

Roofing Systems

Atria Systems

Related Materials

• Joint Sealants

Related Resource Pages

• Air Barrier Systems in Buildings
• Blast Safety
• CBR Safety
• Building Design Considerations In Cold Climates
• Extensive Vegetative Roofs
• Flood Resistance
• HVAC Integration
• Indoor Air Quality and Mold Prevention
• Integrity Testing for Roofing and Waterproofing Membranes
• Seismic Safety
• Structural Insulated Panels (SIPs)
• Sustainability
• Wind Safety

The materials, components, and systems conveyed in these concept diagrams are intended to convey general design principles only. Any resemblance between these details and proprietary or otherwise commercially available materials, components and systems is purely coincidental and should in no way be considered an endorsement by NIBS and/or the individual authors who contributed to the content of this website.

Introduction

Intended Audience and Subject Matter

The National Institute of Building Sciences (NIBS)–under contract from the Army Corps of Engineers, the Naval Facilities Engineering Command, the US Air Force, the General Services Administration, the Department of Energy, and the Federal Emergency Management Agency—has developed this comprehensive federal guide for exterior envelope design and construction for institutional/office buildings.

The scope covers buildings constructed of steel, reinforced concrete, reinforced masonry and reinforced concrete masonry units and includes low-rise, mid-rise and high rise buildings. Typical buildings include administration (office) buildings of all sizes, from a small one-story base administration building to a twenty-story inner city agency office facility. Other building types include firehouses and police facilities, courthouses, military residences, many types of laboratories, various types of education buildings, hospitals, extended care facilities, clinics and many types of recreational buildings. Special use buildings such as airplane hangers, testing facilities, and stadiums, single family residences and wood frame structures are not included.

Though specifically intended for Federal Government agency projects, the information in the guidelines will also be applicable to many privately developed projects—whether of a commercial or institutional nature—which are essentially similar in use and construction to equivalent governmental structures. Because the guidelines are intended for use in the design of governmental structures, the intent is to provide a long-lived structure based on lifecycle costing since governmental ownership is typical in perpetuity. Thus a high standard of construction and maintenance is advised to achieve the aims of the agencies involved.

Format

This is the first time a group of Federal agencies has developed a set of guidelines to be used for the design and construction of their buildings. Its publication and use is meant to assist in the development of uniform design and construction criteria for the Federal government. Instead of taking form as a printed document, which would be revised at long intervals, the Guide is made freely available as a "virtual" information source on the World Wide Web within the Whole Building Design Guide. It is anticipated that government agencies will devise methods of using the Guide to create their own "customized" documents to suit their building types, locations and administrative needs and to further their individual design and construction goals.

Private owners and their designers are free to use the Guide as a resource and can develop their own customized documents or simply refer their designers to useful sections of the Guide. The Guide is not a building code and does not attempt to specify mandatory criteria. Instead it provides design oriented information meant to assist designers in making informed choices of materials and systems to achieve performance goals in their buildings.

The Guide will be a "living" information source that will continually expand and change. It will be interactive, allowing users to enhance the content by adding resource papers, reporting on experiences, and helping to maintain a dialog with Guide management.

The details associated with this section of the BEDG on the WBDG were developed by committee and are intended solely as a means to illustrate general design and construction concepts only. Appropriate use and application of the concepts illustrated in these details will vary based on performance considerations and environmental conditions unique to each project and, therefore, do not represent the final opinion or recommendation of the author of each section or the committee members responsible for the development of the WBDG.

Scope

Richard Rush, in his book The Building Systems Integration Handbook, defines a building in terms of only four systems:

• Structure
• Envelope
• Mechanical
• Interior

In this categorization, "The envelope has to respond both to natural forces and human values. The natural forces include rain, snow, wind and sun. Human concerns include safety, security, and task success. The envelope provides protection by enclosure and by balancing internal and external environmental forces. To achieve protection it allows for careful control of penetrations. A symbol of the envelope might be a large bubble that would keep the weather out and the interior climate in."

Dr. Eric Burnett and Dr. John Straube, in a number of writings, have also described the envelope in terms of performance and function. According to them, the envelope "experiences a variety of loads, including, but not limited to, structural loads, both static and dynamic, and air, heat and moisture loads." The enclosure must then support structural loads and control environmental loads, which include both long-term and short-term loads. The enclosure is also often used to carry and distribute services within the building. In addition, the envelope (primarily the wall) has several aesthetic attributes that can be summarized as finishes. (This description of the envelope is expanded in the wall section of this Guide.) Thus the systems and assemblies of the envelope are one of the four main building systems both in terms of their physical existence and in their contribution to overall building performance.

For this guide the building envelope also includes the below grade basement walls, foundation and floor slab (although these are generally considered part of the building's structural system) so that the envelope includes everything that separates the interior of a building from the outdoor environment. The connection of all the nonstructural elements to the building structure is also included. Finally, it is recognized that the exterior envelope plays a major role in determining the aesthetic quality of the building exterior, in its form color, texture and cultural associations.

The following Building Envelope Systems are covered in separate chapters:

1. Below Grade construction
2. Exterior Walls, both structural (providing support for the building) and nonstructural (supported by the building structure)
3. Fenestration, both windows and metal/glass curtain walls
4. Roofs, both low- and steep-slope
5. Atria.

This guide demonstrates that the design of the envelope is very complex and many factors have to be evaluated and balanced to ensure the desired levels of thermal, acoustic and visual comfort together with safety, accessibility and aesthetic excellence. As can be seen from the list of functions of the building envelope detailed in the Function and Performance section, the envelope plays a role in almost every building function, either directly or indirectly in its relationship to other building systems.

Figure 1 illustrates the envelope systems of a typical building.

The guidelines for each of these systems are authored by an expert in the subject matter and are presented in the following uniform format:

• Introduction—An overall description of the system
• Description—The physical elements and properties of the system
• Fundamentals—A discussion of the design objectives to achieve ranges of performance
• Applications—The range of applications for building functions and external conditions
• Details—Generic construction details in CAD format with commentary
• Emerging Issues—A survey of significant current research and development
• Codes and Standards—Code philosophy and limitations and a summary of currently applicable codes and standards
• Resources—References, major publications, industry and professional associations, and Web sites

In addition, the following performance issues are examined for each of the envelope systems:

• Thermal performance
• Moisture protection
• Fire safety
• Acoustics
• Daylighting and perimeter visual environment
• System maintainability
• Material durability

Beyond these major performance issues the following more specialized building performance topics are covered by separate authors in concert with the principal system authors and, where appropriate, integrated into the main text for each system:

• Seismic safety
• Safety against blast and chemical, biological and radiological (CBR) attack
• Safety against extreme wind
• Safety against flood
• Indoor air quality and mold prevention
• Sustainability and HVAC integration

The Whole Building Design Guide

The Building Envelope Design Guide is one of a series of guides in the Whole Building Design Guide (WBDG) that are intended to assist designers in the integrated design of assemblies and systems. As such, the Building Envelope Design Guide follows the general format of other guides in the WBDG and are internally linked to Resource Pages and other levels and sections of the WBDG.

The Whole Building Design Guide (www.wbdg.org) is an evolving Web-based resource intended to provide architects, engineers and project managers with design guidance, criteria and technology for "whole buildings". Accordingly, the WBDG covers the whole range of today's issues in building design, such as sustainability, accessibility, productivity, and safety—both from human and natural hazards. The WBDG is constantly augmented with updated and new information and is structured as a "vertical portal", enabling users to access increasingly specific information as they navigate deeper into the site.

The concept of the Whole Building Design Guide has been formalized to achieve four main goals:

1. To simplify access to government and non-government criteria and standards information using a web-based approach so that valuable time is not wasted searching for this documentation.
2. To replace outdated, redundant paper-based criteria documents.
3. To guide managers and A&E firms through a "whole building" approach to building design so that high performance, longer-lasting buildings are produced.
4. To provide a brief, up-to-date and informative resource that covers general and specific topics in an encyclopedic form. However, unlike a traditional encyclopedia, the WBDG enables the user to build up a private store of relevant information by direct links to other resources available on the Internet with a few mouse clicks.

The WBDG has become a primary gateway to up-to-date-information on a whole range of Federal and private sector building-related guidance, criteria and technology from a "whole building" perspective. Users are able to access information through a series of "levels" by way of three major categories: Building Types, Design Objectives, and Products and Systems. At a lower level are Resource Pages, which are succinct summaries on particular topics written by experts. Pages within the WBDG are cross-linked to each other, and hyperlinked to external Web sites, publications and points of contact, allowing easy access to related information. Agency-specific information is accommodated in a Participating Agency section. Other features include relevant Federal mandates, news headlines and a robust search engine.

The WBDG Web site is provided as an assistance to building professionals by the National Institute of Building Sciences (NIBS) through the funds and support of the NAVFAC Criteria Office, the U.S. General Services Administration (GSA), and the Department of Energy through the National Renewable Energy Laboratory (NREL) and the Sustainable Buildings Industry Council (SBIC). A Board of Direction and Advisory Committee, consisting of representatives from Federal agencies, private sector companies and non-profit organizations guide the development of the WBDG.

The Evolution of the Building Envelope

The Building Envelope Design Guide will constantly evolve, with its users participating in this evolution rather than simply using a set of fixed, definitive guidelines. They will thus be advancing the evolution of the building envelope itself. The first building envelope that protected humans from the elements was probably a cave that provided a degree of privacy and security. The earliest building envelopes were dome-shaped structures that combined wall and roof (Figure 2A). At an early stage, however, the two dominant forms of envelope evolved, depending on climate and available materials: the timber frame and the masonry wall (Figure 2B and 2C). Early shelters in the warm climates of Africa and Asia used timber or bamboo frames clad with leaves or woven textiles. In other regions and climates heavier indigenous materials such as stone, rock and clay baked by the sun were used to provide more permanent shelter and protection from the heat and cold (Figure 2D).

To this day rural regions in lesser developed countries still construct these forms of shelter. In the developed world we still use envelopes of timber frame and masonry walls, although both have evolved into a wide range of materials—some natural, others synthetic. Roofs evolved independently as waterproof elements with their own set of materials.

Thus, eventually the roof, wall and floor became distinct elements of the building envelope that have continued to this day with very little change in concept, use and even material. A medieval dwelling might have walls of wood, brick or stone, a wood roof structure, a slate tile or thatch roof and a floor of stone or hardened dirt. Such a dwelling can still be found today in many regions of the United States and the world.

To take one element of the envelope, the wall, its basic performance requirements have remained the same from medieval times to this day: protection of the interior from the elements and security for its occupants. However, our expectations have vastly increased, both in terms of absolute performance and the ability to control the impact of exterior water, sunlight and the ambient outside temperature on our interior environment. Depending on a society's structure and economy, such needs as degree of permanence of our exterior system, its scale and adornment and our desire to have a wide variety of exterior envelope choices may also vary considerably.

Figure 3. The ancient and medieval wall on the left attempts to provide all the envelope functions with one material. Later, right, decorative finishes were added to the exterior and interior of the wall.

Compared to most of today's walls the medieval or renaissance masonry wall was simple. Initially the wall was a single homogeneous material—stone or brick-exposed on the exterior and interior. Such walls are still constructed today, although the wall is more likely to be reinforced concrete or concrete block. Before long, the historic wall would become adorned: a rough structural stone would be faced on the exterior with a precisely cut and fitted facing of fine stone or marble, and the interior would be faced with smooth plaster (Figure 3).

As soon as the structural wall became faced with different finish materials the beginnings of variable performance capability emerged. The separation of the structure and facing presaged the layered exterior wall of today. The structure of rough cut stone could rise independently from its facing, which could be prefabricated in the craftsman's shop. The high-quality facing and its detailing also provided protection from the weather for the structural masonry within (Figure 4).

Historic buildings and even historic revival buildings accomplished many of the building envelope functions by default: thick, heavy masonry was fireproof and good for insulation in both summer and winter. It was excellent acoustically and, with sheltering roofs and good water protective details, was reasonably watertight and draft free by the standards of the time. However, by modern standards, the wall had fixed and limited performance capabilities.

Figure 5. The layers of performance. The performance of each layer is variable. Some materials may perform more than one function, and their position in the layer may change according to the climate.

The big change in the concept of the wall—and the real beginning of today's concept of the building envelope—occurred with the invention of the steel, (and later, the reinforced concrete) frame in the nineteenth century. The exterior wall could become a screen against the elements and no longer be needed to support the floors and roof. However, for several decades steel frames were buried in masonry walls, and buildings continued to be designed in gothic or renaissance styles. The modern architectural revolution beginning in the early 20th century changed this and by mid-century the steel or concrete framed office building with its lightweight metal and glass curtain wall had become the new world-wide vernacular for larger commercial and institutional buildings.

When the wall became a nonstructural screen-in and no longer supported the upper floors and roof, it lost the beneficial attributes of mass but gained in providing performance options. Whole new industries arose that would develop insulation and fireproofing materials, air and moisture barriers and interior and exterior facings. More recently the exterior wall has become a major subject of building science studies, largely because of the wall's key role in managing heat gain, heat loss and moisture penetration. As a result, the modern wall now consists of a series of performance "layers" (Figure 5).

A cross section of a typical layered exterior wall of today illustrates the complexity that this approach leads to in practice (Figure 6).

Figure 6. This section through a typical nonstructural exterior wall within a steel frame building structure shows the complexity of the layered approach in its application. Photo Credit: Architectural Graphic Standards

A different material may achieve each performance requirement, with each performing a separate function, or some materials may perform multiple functions. For example, the air barrier may simply be a coating on a support layer.

Function and Performance

The complexities of today's wall can also be exemplified by listing its functional requirements, or needs that must be met. There are at least 13 distinct needs, as listed below. Most of these functions also apply to fenestration and the roof and a few also apply to below grade construction (see Table 1 in Section 7). Each function (with a few exceptions) has its own performance standards and methods of measurement, methods of testing for compliance, and acceptability criteria.

1. Structural: If the wall is not part of the main building structure, support own weight and transfer lateral loads to building frame.
2. Water: Resist water penetration.
3. Air: Resist excessive air infiltration.
4. Condensation: Resist condensation on interior surfaces under service conditions.
5. Movement: Accommodate differential movement (caused by moisture, seasonal or diurnal temperature variations, and structural movement).
6. Energy conservation: Resist thermal transfer through radiation, convection and conduction.
7. Sound: Attenuate sound transmission.
8. Fire safety: Provide rated resistance to heat and smoke.
9. Security: Protect occupants from outside threats.
10. Maintainability: Allow access to components for maintenance, restoration and replacement.
11. Constructability: Provide adequate clearances, alignments and sequencing to allow integration of many components during construction using available components and attainable workmanship.
12. Durability: Provide functional and aesthetic characteristics for a long time.
13. Aesthetics: Do all of the above and look attractive.
14. Economy: Do all of the above inexpensively.

Performance refers to the desired level (or standard) to which the system must be designed for each of the above functional requirements. For example, what dimensions of movement must be accommodated, and what is the expected useful life, or durability, of the system.

Cost Management

The building envelope represents a substantial percentage of a building's cost. (Some typical costs presented as a percentage of the whole building cost are shown in Table 1, below.) For a multi-story building, the envelope costs (dominated by the cost of walls and fenestration) may even exceed 20% of the total building construction cost.

The envelope is also a critical system in the determination of the overall performance of the building, with an emphasis on the thermal environment, lighting and acoustical characteristics. It is the prime determinant of the exterior aesthetic quality of the building. Clearly, the balance between the cost of the building envelope and its levels of performance will be of great importance in achieving the most cost-effective design of a building.

(Source: Means Square Foot Costs)

The Building Envelope Design Guide does not attempt to provide cost information for estimating purposes. There are a number of reasons for this:

1. Construction costs fluctuate and rapidly become out of date. Published indices attempt to ameliorate this problem but they tend to be very broad in scope and are of limited use in application to a specific project. Also the state of the local market at the time of bidding and construction often has a major effect on cost.
2. Construction costs vary greatly according to the project location. In broad terms, in the U.S. there is approximately a 200% spread between the least and most costly states in terms of construction cost.
3. Very rapid change in cost—generally upward—in such key materials such as steel and lumber are common and cannot be predicted in advance.
4. Government agencies and other institutions and businesses that manage large construction programs generate detailed cost information that refers particularly to the type and quality of the buildings they construct. This forms a valuable database that is specific to the owner's location and needs. Architectural and engineering firms and contractors also develop cost data that applies to their projects.
5. Specialty construction cost estimating and management firms develop very large and detailed databases on cost because they are focused entirely on cost management issues. On any significant project they should be employed from the outset as part of the design team with responsibilities for cost management.

For these reasons, the developers of the Building Envelope Design Guide believe that cost management should be based on local information procured before the design process for budgeting purpose and during the design process for cost management purposes. The use of life-cycle costing, economic analysis and value engineering can be used to the extent that they suit the owner's economic goals. Clearly an agency or institution that expects to own a building for its entire useful life is well advised to budget on a life-cycle, and many government agencies now require that this be done.

Private owners may have other aims, but the ultimate building operators will all benefit from a building in which life-cycle costs have been considered. A future in which it is clear that energy costs must be expected continually to rise—with the possibility of energy itself becoming scarce within today's building lifetime—makes it the more necessary to design for minimum energy usage consistent with meeting functional and environmental needs. Building envelopes designed with opportunities for the use of day lighting and natural ventilation obviously can play a major role in such considerations.

Function, Performance, Design and Construction Relationships

The systems and elements that comprise the building envelope are each discrete assemblies that, in many instances, are designed by specialist consultants and installed by specialist sub-contractors. The mechanical system, for example, will be designed by a specialist engineering consultant and installed by several different mechanical sub-contractors. Some assemblies have a variety of methods of design and procurement. A metal and glass curtain wall may alternatively be a proprietary catalog assembly, a custom assembly designed by the architect with input from manufacturers or a consultant, or designed by a consultant to meet the architect's requirements. Each system, however, also has functional, performance, design and construction relationship to others.

Functional performance for the thermal environment, moisture protection, sustainability and durability are shared by all 4 of our major subsystems: walls, fenestration, roofing and below grade. Thus each has to be designed to contribute its appropriate share of the overall functional effectiveness in meeting the performance requirements for the whole building. Acoustic performance for the exterior is the responsibility of the wall system and, to a lesser extent, the fenestration, while daylight transmission and control is the responsibility of the fenestration and the roof (if there are skylights, although these will be designed by the fenestration designers). Natural ventilation, if provided, will be a fenestration design problem but will also have major repercussions on the HVAC design. If the HVAC system employs perimeter heating or cooling this must be integrated with the envelope performance requirements. Interior air quality is primarily an HVAC issue, mainly concerned with outside air supply and filtering. The exterior wall will also have some performance requirements relating to materials and permeability.

These relationships and some others are "flagged" in the matrix shown in Tables 2 and 3. Table 2 shows the list of basic performance requirements that are covered in this guide. Table 3 shows the list of secondary performance requirements that are covered. In addition, aesthetics is shown as an "influence". Unlike the other performance requirements, aesthetics is not subject to scientific testing and measurement. Nonetheless—particularly for the wall and fenestration systems of the building envelope—it is a powerful influence in the system and material selection process. The attributes of color, texture and pattern are familiar. The attribute of "association" refers to issues such as the use of stone to represent solidity and permanence (besides its possible measurable attributes of durability), or the desire of some colleges to require red-tile roofs on new campus buildings.

The group of practice considerations refers to issues that appear in all systems and are critical to the successful implementation of the whole project, from concept to commissioning. Innovation refers to emerging methods, materials and processes that may improve the performance, cost or appearance of a system as a whole or any element of it.

Key:
X   Major determinant or influence
(X)   Minor determinant or influence

Key:
X   Major determinant or influence
(X)   Minor determinant or influence

The functional and performance relationships shown are also accompanied by physical connectivity. Many of the building envelope assemblies are connected to and supported by the building structure. Since the envelope receives certain loads—such as wind and seismic, and, in some instance—blast, its members must be capable of distributing these loads to the building structure besides resisting them within their own subsystems. Obviously, if the HVAC system employs perimeter heating and cooling, the distribution system will be part of the overall building HVAC distribution. The physical relationship of the roof assemblies to the structure is critical to their performance.

These relationships mean that the building envelope cannot be designed in isolation. It is a function of design management to ensure that the performance attributes and the physical connections between the envelope and the rest of the building are integrated in concept and execution from the commencement of the design process.

Safety, Security and Building Codes

Safety has long been the traditional focus of building codes, starting with the earliest codes related to fire safety. Protection against earthquakes has been the subject of codes in seismic regions for the last three quarters of the twentieth century. These codes have become very highly developed and have a strong engineering and scientific base assisted by governmental, institutional or industrial programs of research and development. Some codes also mandate requirements for floods and high winds, but these are much less developed than those for earthquakes.

In general, the intent of codes has been to mandate minimum standards that provide acceptable safety at an affordable cost. While codes also provide some property protection, this has not been a major target and has not been a stated intent of the codes. Many features of building codes are understood to represent a minimum standard and in practice are almost always exceeded for reasons of comfort and amenity. For example for many decades all U.S. building codes have agreed that the minimum floor area of a bedroom is 70 square feet with a minimum dimension of 7 feet in any horizontal direction; however, few bedrooms in even the most economical tract house are of this size.

Codes that do not appear to offer an accepted everyday benefit—and that are seen as adding cost to the project—are all too often treated as a maximum. This has created problems when buildings correctly designed and constructed to a seismic code have suffered significant damage—which the code permits, provided that life safety is not compromised. In part owing to the success of codes in protecting public safety, attention has begun to shift toward property protection because of the large economic losses incurred by earthquakes, high winds and floods. This loss is only partly due to the cost of repair and reconstruction; deeper economic losses are incurred by business and service interruption and losses such as market share and tourism.

As a result, designers are being encouraged to create designs for performance against natural hazards that are appropriate for a building's occupancy, function and importance. This means designing for an acceptable level and type of damage. This also generally means designing for performance above that anticipated by normal code-conforming design.

Another development in design against natural hazards has been the encouragement of multi-hazard design. The intent here—as in many other developments in the design process—is to implement a higher level of design integration. This involves ensuring that buildings subject to more than one natural hazard—for example both floods and earthquakes—take advantage of design methods that assist in countering all the hazards that apply and identify and find solutions for those instances where measures may conflict. Thus while elevating a building above grade is an excellent solution for design in a flood plain, great care must be taken to avoid "soft first stories" that have proven disastrous in earthquakes.

While building safety has traditionally focused on natural hazards, building security is focused on societal and political hazards—those created by criminal or disaffected members of our own society or foreign elements that see the U.S. as an enemy. Some degree of concern has always been present in design, of which keys and locks are the most familiar. Remote surveillance systems have been around for some time in retail stores and other sensitive environments. The tragedy of September 11, 2001 and the condition of war that has existed since that time have thrown a much more intense light on the need for building security.

The major difference between attack hazards and natural hazards—beyond a deliberate attempt to damage the building and cause casualties—is that of probability. Although natural hazards vary greatly in probability there is considerable statistical information on the issues of where, how big and how often a given hazard will occur, and considerable scientific study is devoted to this topic. Human-caused hazards have very little history, and the relatively few instances provide a very poor statistical database. As a result, it is at present very hard to know the extent to which it is prudent to take steps to mitigate attack by blast and/or chemical, biological and radiological (CBR) weapons. Meanwhile, much research and development is underway, ranging from testing vehicle barriers to the development of building code provisions that reduces the risk of progressive collapse from damage as a result of bombing.

This is an area that may be expected to evolve rapidly. Some of this evolution will be technical. Some will be societal and political as it begins to become apparent how large and how long-term the threats remain. The questions of where, how big and how often need much more convincing answers than are available at present before the full impact on building design can be gauged. Meanwhile, this subject is superimposed on the traditional range of issues with which the designer must grapple. Again, the need is for design integration with of security concerns considered from the outset.

Innovation

Although many historic materials are still in use—roofs are still constructed of copper and slate, and walls employ natural stone—the building envelope has been a prime target of innovation since the first quarter of the twentieth century. Innovation has been most significant in the wall and fenestration systems of the envelope and has been driven by four main influences:

• Cost reduction for a competitive market
• Enhanced performance
• Material innovation and industrial research & development
• Aesthetics

These influences are all related to one another. Much industrial research and development has been aimed at obtaining a competitive edge through performance improvement or cost reduction. For example, pre-cast concrete fabrication enjoyed about two decades of great success because the material and shapes appealed to architects. Innovation in pre-casting techniques, form design and fabrication and surface finishes resulted from collaboration with architects and the effort to be competitive as a supplier. Ultimately, however the pre-eminence of the pre-cast panel fa¸ade was seriously threatened by the rise of glass fiber reinforced concrete, a synthetic material innovation that was lighter and more economical than concrete and more easily formed into sculptured shapes.

The construction industry is intensely competitive. Much of this stems from the traditional approach to contractor and supplier selection—the competitive bid. This places a premium on lowest cost, resulting in innovation by contractors and sub-contractors trying to get an edge on their competitors. Another aspect of cost is that of reduction in construction time, which translates into cost reduction for a building project's entire stakeholder. Thus, for example, the separation of the building envelope wall and fenestration from the structure enabled the structure to be erected faster, while prefabricated components such as curtain wall assemblies and pre-cast panels were fabricated off-site.

The effort to reduce on-site labor through componentization also originated in the effort to reduce costs and construction time. It is noteworthy that the building industry was able to achieve extraordinary feats of construction time using traditional materials when labor costs were low. For example, the Empire State Building in New York City was constructed in just over 12 months—at the height of the great depression—by laborers working 24 hours a day for a contractor who used the first fast-track scheduling process. A booming construction industry and post-war labor costs soon made such an approach prohibitive.

Aesthetics has also been a powerful influence on the envelope. The most significant application—that of the development of the curtain wall—depended initially on the creation of a market by architects. Since the first all-glass skyscrapers were sketched by Mies van de Rohe in 1919 and 1921 (Figure 7), architects strove to achieve ever simpler and purer glass forms.

The metal and glass curtain wall became a feature of some of the seminal works of the International Style that dominated world-wide design after World War II. Le Corbusier's Pavilion Suisse, Paris (Figure 8A) designed in 1929 was one of the most influential. The most significant development of the curtain wall, however, occurred in the United States. First designed as an expensive, refined and elegant custom artifact, it gradually became a standard commodity, and today is the least costly way to enclose a structure. Perhaps more important, for several decades the glass box perfectly symbolized, in its image of contemporary elegance and modernity, the aspirations of American corporate architecture from Wall Street to Main Street. The United Nations building of 1947 (Figure 8B) and the Lever Brothers building of 1952 (Figure 8C) had enormous impact on architects and owners alike. Within a few years every city in the U.S. had its blue, glass-curtain walled cubes, from corporate headquarters to modest savings and loan branches (Figure 8D). Today, very refined custom walls are still being conceived that can demonstrate an extraordinary scale and delicacy (Figure 9).

Many problems, such as leakage and obtaining pleasing glass colors, had to be solved in early curtain walls. Manufacturers and influential architects working together managed to do so. The first curtain walls were expensive, custom-made assemblies. The proprietary curtain wall has now evolved into the least expensive way of cladding a building. However, very refined custom walls are still being conceived that can demonstrate an extraordinary scale and delicacy. (Figure 9)

Figure 9. Suspended curtain wall, AOL/Time Warner building, New York, 2003. James Carpenter, glazing consultant; Skidmore, Owings and Merrill, Architects.

Future innovations still in their infancy are the double-skin curtain wall that aims to provide controlled natural ventilation and hybrid systems that aim to achieve substantial energy savings as a hedge against an uncertain energy future. (Figure 10)

Figure 10. Hybrid mechanical and natural ventilation with double skin façade. Minerva Tower, London. Nicholas Grimshaw, Architect; Roger Preston & Partners, services engineers.

Conclusion

A number of categorizations of the systems or subsystems that comprise a building are in existence. Richard Rush, in his book The Building Systems Integration Handbook, defined only four systems:

• Structure
• Envelope
• Mechanical
• Interior

Thus the systems and assemblies of the envelope are one of the four main parts of the building both in terms of their physical existence and in their contribution to overall building performance. The envelope protects the other systems from harsh aspects of the outside. It also works in conjunction with the other systems to ensure a safe and benign environment for the building occupants. Thus the envelope is a gatekeeper, allowing certain aspects of the exterior into the building, rejecting some and changing the nature of others. The design of the envelope is very complex and many factors have to be evaluated and balanced to ensure the desired levels of thermal, acoustic and visual comfort together with safety, accessibility and aesthetic excellence.

This guide provides information and recommendations to assist the designer in achieving their goals. While levels of performance are discussed and many quantitative criteria are explained, no mandatory requirements are stated. Those are the purpose of building codes and regulations. This guide assumes that any design work will conform to code requirements but deal also with many functions that, while not subject to code, are essential for building excellence.

Introduction

A Building Information Model (Model) is a digital representation of physical and functional characteristics of a facility. As such, it serves as a shared knowledge resource for information about a facility forming a reliable basis for decisions during its life cycle from inception onward.

A basic premise of Building Information Modeling is collaboration by different stakeholders at different phases of the life-cycle of a facility to insert, extract, update or modify information in the Model to support and reflect the roles of that stakeholder. The Model is a shared digital representation founded on open standards for interoperability.

Some have identified BIM as dealing with only 3D modeling and visualization. While important and true, this description is limiting. A more useful concept is that a Model should access all pertinent graphic and non-graphic information about a facility as an integrated resource. A primary goal is to eliminate re-gathering or reformatting of facility information; which is wasteful.

Non-value added effort or waste is a significant problem in the construction industry. Much of the waste comes from inaccurate or entrusted information causing the information to have to be re-gathered multiple times throughout the life of the project. This waste has been identified to be 57% in the construction industry by a chart prepared by the Construction Industry Institute and Lean Construction Institute. While waste in the manufacturing sector was identified to be 26%. This 31% variance when plotted against the 2008 design and construction spending projections by Engineering News-Record comes out to nearly $400B annually. This number does not include operations and sustainment, which would jack the number up through the ceiling, as if it were not high enough already. The primary beneficiary is the owner. However, many owners seem to be content to pay the freight of design and construction, whatever the cost and have been rather lethargic to push for change to date. The construction industry, however is seeing benefit to implementing BIM on their own and is pushing forward at a rather rapid rate for this traditionally conservative industry.

BIM standards have many objectives but one of the most important is to improve business function so that collection, use and maintenance of facility information is a part of doing business by the authoritative source and not a separate activity.

The scope of BIM is from the smallest part rolled up to the world or portfolio view, from inception onward in the lifecycle of a facility and includes all stakeholders that need facility information from the designers to the occupants.

Numerous organizations have initiatives underway to develop a National BIM Standard. The following sections provide links and describe the efforts underway to develop a standard for information sharing that will help weave all stakeholders into a common fabric.

Relevant Codes and Standards

• National BIM Standard-United States® (NBIMS-US™) by the National Institute of Building Sciences, 2015. The NBIMS-US™ provides consensus based standards through referencing existing standards, documenting information exchanges and delivering best business practices for the entire built environment. The National Institute of Building Sciences BIM Council, through the NBIMS-US Project, works to establish the standards needed to foster innovation in processes and infrastructure so that end-users throughout all facets of the industry can efficiently access the information needed to create and operate optimized facilities.

Major Resources

Government Initiatives

• Tri-Service CAD BIM Technology Center The CAD/BIM Technology Center explores new CAD and BIM technologies for facilities, infrastructure, and environment within DoD.
• Naval Facilities Engineering Command (NAVFAC) Building Information Management and Modeling (BIM) The Navy is the first federal government agency to leverage Building Information Management and Modeling (BIM) to acquire Facility Electronic Operation and Maintenance Support Information (eOMSI).
• Air Force Building Information Modeling for MILCON Transformation The Air Force is utilizing the BIM environment to meet its MILCON Transformation goals and objectives.
• Defense Health Agency (DHA) Building Information Modeling (BIM) The Military Health System (MHS) was the first healthcare system in the U.S. to implement the use of BIM across the facility lifecycle.
• General Services Administration (GSA) GSA was the first government organization to lead the U.S. government into BIM and had a primary role in promoting BIM in the entire industry. They remain today a leader in the initiative, continually breaking new ground.
• Department of Veterans Affairs (VA) VA is committed is committed to utilizing BIM to support the delivery and management of world-class healthcare for our nation's veterans.

Introduction

Photovoltaic (PV) technology is an ideal solution for the electrical supply issues that trouble the current climate-change, carbon-intensive world of power generation. PV systems can generate electricity at remote utility-operated "solar farms" or be placed directly on buildings themselves. Their fuel source is simple sunlight, and they produce electricity without the negative environmental consequences associated with other power generation methods. They are silent and reliable. The size of PV installations can range from extremely small to enormously large. They can be scaled down for small loads like specific site luminaires, remote communication devices, and individual water pumps; or they can occupy hundreds of acres and generate enough electricity to power thousands of buildings.

For building installations, PV systems fall into two categories, building applied photovoltaics (BAPV) and building integrated photovoltaics (BIPV). BAPV is the more common type of installation, with the solar collectors located completely outside of the building envelope. Roof-mounted, ballasted solar arrays placed on top of the roofing material are BAPV assemblies. A BIPV installation is when the photovoltaic collectors are an integral part of the building envelope. They can either replace exterior shell components or be integrated into them. Examples of BIPV components and materials currently on the market include: PV glass windows, PV glass skylights, awnings, balustrades, canopies, shingles, exterior wall panels, and even PV walkable surfaces.¹ Not only do BIPV systems generate electricity, but they can add visual interest and aesthetic design elements to the building.

Building Integrated Photovoltaics (BIPV) are when the photovoltaic collector elements are located directly within a building's envelope (or canopy structure). Photo Credit: U.S. Department of Energy / EERE

Building owners and utilities all benefit with the implementation of PV systems. The contribution of PV generated electricity can have major impacts on the peak demand loads that utilities have to provide power for. Late afternoon sunshine and heat accumulation in buildings lead to greater requirements placed on air conditioning systems to keep occupants cool. A building-located photovoltaic system takes advantage of these same sunshine conditions to provide electricity for the building while simultaneously lessening the pressure on the utility grid to increase electricity production. The use of photovoltaics lowers the overall U.S. carbon footprint for electricity generation.

Solar energy installations have an impact on the fuel sources used by utilities to generate electricity for the grid. As PV generated power increases in the energy infrastructure, the use of higher carbon-footprint generated electricity decreases. Image Credit: Ronald Fergle based on a graphic by Lena Hansen and Virginia Lacy of the Rocky Mountain Institute

A building's self-consumption of the electricity generated by its PV system improves the cost-effectiveness of the installation. Buying electricity from the grid costs more than revenue achieved by selling electricity to the grid. Utilizing batteries to store PV electricity for later use can dramatically reduce the need for grid-supplied electricity. The potential for including battery storage in a PV system design should take into consideration the building loads, the time of day, the available PV generated power, and the costs for various levels of battery storage. Properly sized systems can be cost-effective for consumers.

The self-consumption of PV generated electricity coupled with battery storage can significantly reduce the need for grid-supplied electricity. Image Credit: Ronald Fergle based on a graphic by Ralf Haselhuhn.

Depending on the fuel source, generation of electricity at a utility power plant can be inefficient and carbon-intensive, while simultaneously causing the release of Greenhouse Gasses (GHGs) and harmful fine Particulate Matter (PM_2.5). In addition, of the electricity that enters the grid from a power plant, the U.S. Energy Information Agency (EIA) estimates that 5% is lost due to transmission and distribution (T&D) inefficiencies.² Distributed Energy Resources (DERs) such as BIPV systems, do not have these negative environmental impacts. Solar energy is a clean, renewable energy source, and the electricity generated is already located at the point of use. For more information regarding Distributed Energy Resources, refer to the energy.gov website.

Description

Photovoltaic Technologies

The categories of common photovoltaic technologies used in BIPV applications include:

1. Crystalline silicon (c-Si): Solar cells made from solid crystalline silicon wafers (mono-crystalline or poly-crystalline/multi-crystalline) can deliver approximately 20 watts per ft² of PV array. Versions of these cells may incorporate additional layers of solar absorption materials in order to increase electrical production. Individual cells are wired together and assembled into modules at factories before being shipped to project sites.

2. Thin-film: These products typically incorporate very thin layers of photovoltaic compounds that have been deposited on substrate materials using plasma enhanced, chemical vapor deposition (PECVD) processes. Commercial thin-film materials deliver about half the watts per ft² of PV array area compared to c-Si modules. Thin-film products can be rectilinear modules, rolled-out surfaces, or take the shape of an underlying architectural element. This category includes: copper indium gallium (di)selenide (CIGS), cadmium telluride (CdTe) and amorphous silicon (a-Si) cells.

3. Emerging-PV: These technologies include dye-sensitized solar cells (DSSC), Perovskite cells, organic cells, and quantum dot cells, among others. Efficiencies in laboratory environments range from 13% to 26%. Cells in this category can exhibit properties of transparency, flexibility, or color; and they require lower energy expenditures to create.

The DSSC cells represent a new type of solar cell that require less energy-intensive materials to manufacture, and because of their simplicity can be less costly to produce. These cells are comprised of three basic parts: the front-side glass transparent conducting oxide (TCO) electrode, an interior electrolyte solution, and a back-side counter electrode. The inside surface of the front glass is first sintered with a transparent anode, e.g., fluoride-doped tin dioxide (SnO₂:F) to make the TCO. Then it is covered with titanium dioxide (TiO₂) nanoparticles coated with photo-sensitive dyes. When the dyes are exposed to sunlight their electrons are energized and elevated into the conduction band of the TiO₂. From there they migrate to the TCO anode material. After flowing through an external circuit as electricity, the electrons re-enter the DSSC cells through a back-side counter electrode surface. The liquid electrolyte then transports the electrons back to the dye materials to re-oxidize them.

A schematic showing the movement of electrons in the DSSC photovoltaic process. Image Credit: Ronald Fergle

A PV installation includes:

1. PV Modules: These "solar collectors" can be crystalline, thin-film, or one of the emerging PV technologies. They can be transparent, semi-transparent, or opaque.

2. Balance of System (BOS) Components: This includes everything in a PV installation other than the solar collectors.
   • Module Mounting Systems
   • Wiring, Combiner Boxes, DC Disconnects, and AC Disconnects
   • Inverters
   • Electrical Distribution Panels
   • Batteries

PV Modules: These components are where the conversion of sunlight into electricity actually occurs. Energetic photons in sunlight excite electrons in the semi-conductor materials which elevate them to a higher energy conduction band. The electrons then become free to move as electricity within an external circuit. The electricity coming from PV modules is always Direct Current (DC).

Module Mounting Systems: BIPV mounting systems use clips, bolts, or adhesives to fix the modules directly to the envelope structure. Photovoltaic glass units for façade or roof applications are installed similarly to windows or skylights, but with DC cabling attached. For BAPV installations these systems usually consist of metal frameworks called racking. They can be constructed to create fixed, saw-tooth arrangements or flat planes that are located close to the roofing surface. Typically weights or heavy blocks are used to secure the racking in place.

Wiring, Combiner Boxes, DC Disconnects, and AC Disconnects: These are the components that facilitate and address the flow of electricity in the installation. Individual wiring from groups of modules can be combined into single cables in combiner boxes for circuit simplicity and to reduce the overall amount of wiring material. Combiner boxes also provide over-current protection. DC Disconnects and AC Disconnects are switches located at strategic points in the installation in order to disconnect or curtail the flow of electricity.

Inverters: These units convert the DC electricity coming from the PV modules into AC electricity. String invertors handle the output from multiple modules, and micro-inverters are dedicated to a single module.

Electrical Distribution Panels: This is the location where PV installations interconnect with a building's electrical infrastructure. Power coming from the PV system is wired into the distribution panelboard as an individual circuit. The circuit breaker on this circuit is referred to as the Over Current Protection Device (OCPD) and subject to specific sizing requirements.

Batteries: These devices store power for use at a later time. The energy flow into and out of the battery storage system is determined based on user-specified parameters or building energy management system (BMS) directives. Batteries are commonly used to store power generated from the PV array during sunny periods, and then provide that power later on to help meet the facility's energy requirements.

For more detailed information on PV module technologies and BOS Components, refer to the related discussion on the WBDG PV page.

A simplified guide for how PV modules can be connected to power optimizers, string inverters, or micro-inverters based on system design objectives. (System schematics, including combiner boxes and disconnect switches, vary based on project parameters and equipment used.) Image Credit: Ronald Fergle

Building Integrated Photovoltaics (BIPV) System

Building Integrated Photovoltaics is the implementation of photovoltaics as part of the building envelope. The solar collectors serve the dual function of protecting the structure from external environmental conditions, as well as being a source for electrical power. While the BIPV system itself has an initial financial cost, because it potentially replaces other building materials the overall costs of the envelope may not increase significantly. BIPV systems can also reduce HVAC electrical requirements and cooling costs when the modules are used to shade the building. When all of the advantages are taken into consideration, BIPV installations can be viewed as financial investments. They have an up-front cost, but in turn they can significantly reduce or eliminate a building's yearly energy costs, pay for themselves, and provide building owners with continuing economic savings. A recent study has documented how BIPV installations have a positive return-on-investment (ROI), and even north-facing facades can be economically feasible.³

Design Of A Building Integrated Photovoltaics (BIPV) System

The process of designing a BIPV system is not unlike that for other building systems. Decisions should take into consideration life-cycle cost analyses in addition to up-front costs, installation procedures, performance expectations, and O&M requirements. However, with BIPV installations the aesthetics are also important and should be taken into account.

Steps in designing a BIPV system overlap, in that the consideration of one topic may impact the resolution for another. A successful solution addresses all concerns simultaneously. The general list of topics includes:

1. Energy Conscious Building Design: This strategy reduces overall energy use, enhances comfort, and saves money while also enabling the BIPV system to provide a greater percentage of the electricity required.
   • Daylighting: The use of sunlight and light from the skydome to illuminate interior building spaces. This reduces the electrical loads and heat generated from light fixtures.
   • Thermal Mass: Taking advantage of a material's ability to store and release heat energy in order to even out interior building temperature fluctuations.
   • Natural Convection: Using the natural properties of air circulation to ventilate, heat, or cool interior building spaces.
2. Type of PV System: Determine if the system will be grid-connected, grid-connected with battery backup, or stand-alone.
   • The majority of BIPV systems are tied to a utility grid, which in effect uses the grid as storage and backup. The system type and configuration should be developed based on the priorities of the owner, which could include: budget limitations, space constraints, electrical requirements, energy independence, and aesthetics, among others.
   • For stand-alone systems powered by PV alone, the system, including battery storage, should be sized to meet both the building's peak demand loads and the lowest power production projections of the PV array. Installations like these typically include a backup generator for unusual or excessive peak loads.

3. Location of Installation: Any exterior building surface is a potential location for a BIPV installation. Roof elements include: photovoltaic shingles, rolled thin-film surfaces, and PV glass skylights that have PV cells or transparent PV surfaces incorporated into them. Wall possibilities include: siding with integrated PV surfaces, PV glass windows that contain PV cells or PV coatings, and shading devices that are also PV collectors. Railings, carports, and covered entryways are additional locations. As part of the PV component selection process it is important to consider how the collector surfaces will be attached to the sub-structure. Manufacturers of PV components provide detailed information regarding mounting requirements.

4. Building Electrical Load Analysis: Consider the building's electrical usage patterns and adjust loads if possible to reduce peak levels. Depending on the building type (or functions occurring within the structure), shifting when power is required can reduce demand spikes and the peak loads they place on the PV system. Examples of flexible tasks include: meetings that require lighting and space conditioning, optional machinery processes, operation of dishwashers or laundry facilities, and heating of hot water for thermal storage. Electrical demands are typically greater in the afternoon because of HVAC cooling loads, so when non-time-sensitive tasks can be moved to the morning hours, the peak afternoon loads become less. Installing motion detectors on lighting systems and turning off office equipment when not in use are simple strategies to reduce power demands. It has also been shown that educating building occupants about the benefits of reducing plug-loads helps to achieve lower energy use.⁴ In addition, it may be worthwhile to incorporate battery storage to reduce the purchase of electricity during the more expensive power demand periods.

5. Provide Adequate Ventilation: PV performance efficiencies are reduced by elevated operating temperatures. This affects crystalline silicon PV cells more than amorphous silicon thin-films, but all PV cells are susceptible. To improve conversion efficiency, allow appropriate ventilation behind the modules in order to dissipate heat.

6. Consider Using PV Modules to Filter Direct Sunlight: When using semi-transparent thin-film modules or semi-transparent crystalline modules (where the PV cells are placed apart from each other between two layers of glass), it is possible to create unique daylighting features in facades, roofing, or skylight PV systems. These elements can help reduce unwanted cooling loads and the glare associated with large expanses of architectural glazing.

7. Incorporate PV Modules as Shading Elements: PV arrays can double as awnings over view-glass areas of buildings and can provide appropriate shading. When sunshades are considered as part of an integrated design approach, chiller capacity can often be smaller and perimeter cooling distribution reduced or even eliminated.

8. Design for the Local Climate and Environment: It is important to understand the impacts of climate and environment on the array output. Cold, clear days will increase power production, while hot, overcast days will reduce array output. Typical considerations include:
   • Surfaces reflecting light onto the array (e.g., snow, lakes, or wide rivers) will increase the array output.
   • Potential snow- and wind-loading conditions may require additional bracing or structural analysis.
   • Modules angled more vertically will shed snow quicker.
   • Horizontal modules and arrays located in dry, dusty environments, or environments with heavy industrial traffic or pollution, will require periodic rinsing with water to limit efficiency losses.
   • c-Si modules have higher efficiencies and perform best in clear sky conditions, but their power output decreases significantly in cloudy or shady situations. While DSSC, CdTe, a-Si, and CIGS cell types have lower efficiencies compared to c-Si, they are less affected by cloudy or overcast conditions.

9. Address Site Planning Issues: Early in the design phase, ensure that the solar array will receive maximum exposure to the sun and will not be shaded by site obstructions such as nearby buildings or trees. It is important that the system be unshaded during the peak solar collection period consisting of three hours on either side of solar noon. The impact of shading on a PV array can be significant.

10. Consider Array Orientation: Array orientation and tilt impacts the annual energy output of a system. Arrays tilted towards the Sun generate 50%–70% more electricity than vertical façade installations, and southern facing arrays maximize power generation. However, advancements in PV technologies have increased the flexibility of array design; so it may be possible to tune the electrical output of a system to be closer to the time of day the power is required. Certain module types may be more effectively used facing east for the morning solar gain, or west for the late afternoon sunlight conditions (CdTe, CIGS, DSSC, and a-Si thin-films), and high-gain modules (typically c-Si) can be aligned slightly west of south so they produce more electricity during the afternoon peak building demand loads. As the costs for PV installations continue to decrease, the strategy to provide more continuous power generation becomes more affordable. Portions of arrays that are oriented to the east or west may not be as high in efficiency or produce the sheer volume of electricity that the southern facing portions do, but they can provide additional power closer to the time that some building loads require it.

11. Use Credentialed Professionals: Ensure that the designers, installers, and maintenance professionals involved with the project are properly trained, licensed, certified, and experienced in PV systems work. They should be knowledgeable of the latest advancements in commercially available technologies, products, and installation practices.

Solar insolation levels can vary based on building surface orientation. While surfaces tilted towards the Sun receive the most energy, secondary and tertiary surfaces can still contribute meaningful amounts of PV generated electricity. Image Credit: Ronald Fergle based on a graphic by Polysolar Ltd.

Application

BIPV systems can be designed to blend in with traditional building materials and appearances, or they may be used to create a more innovative aesthetic. The examples below show how PV modules can become attractive elements of building exteriors. Photovoltaics may be integrated into numerous assemblies within building envelopes, including:

• Facades: Solar cells can complement or replace traditional view windows or spandrel glass. While these installations are on vertical surfaces, which reduce the intensity of the solar insolation, the overall size of a facade can help compensate for the reduced power per unit area.

• Awnings: Photovoltaics may be incorporated into awnings or slightly sloped, saw-tooth canopy designs. Semi-transparent modules provide filtered sunlight underneath while affording additional architectural benefits such as passive shading.

• Roofing: The use of PV in roofing systems can provide a direct replacement for batten and seam metal roofing, traditional 3-tab asphalt shingles, and ceramic tiles. Note that these types of installations require adequate ventilation in order to keep the cell temperatures cooler.

• Skylights: Using PV for skylight systems can be both an economical use of PV and an interesting design feature. Just as with PV windows, the semi-transparency enables visual connections to the exterior environment while providing diffuse natural lighting.

An example of the aesthetic potential of BIPV is the SwissTech Convention Center (STCC) on the Ecole Polytechnique Federale de Lausanne (EPFL) Ecublens, Switzerland, campus. The southwest façade contains 280 m² of 355 integrated Die-Sensitized Solar Cells (DSSC), also called Grätzel cells, arranged within 65 columns of various heights. The system provides 3 kWp of electricity. The transparent DSSC installation filters direct afternoon sunlight entering the convention center main lobby; while at the same time providing a visual connection to the exterior environment with views to the sky, neighboring buildings, trees, and passersby.

Exterior views of the SwissTech Convention Center southeast façade (left) and southwest façade (right). Photo Credit: Ronald Fergle

Interior views of the DSSC modules exhibit a canvas of translucent vertical ribbons of color with the blue sky in the background. As the sun progresses through the sky, the colorful shadows cast from the modules move across the lobby floor. Photo Credit: Ronald Fergle

The light-weight modules are mounted to metal bars on the exterior side of the window glazing. The electrical cabling runs within channels next to the windows. Photo Credit: Ronald Fergle

Examples of c-Si wafers being used in innovative ways include the Energiewürfel building in Konstanz, Germany, and the Ludesch Community Centre in Vorarlberg, Austria. The modules have dual-glass surfaces with individual, perforated c-Si wafers spaced evenly inside. The installations filter direct sunlight while simultaneously providing views beyond. The Energiewürfel large-format, south-facing window installation has a 22% transparency, and when combined with the PV roof installation generates 23.2 kWp of electricity. The 350 m² Ludesch Community Centre canopy is comprised of 120 slightly-sloped modules oriented to the southwest, and generates 16,000 kWh/yr of electricity. The canopy emphasizes the exterior gathering area while protecting visitors from rain and snow.

Semi-transparent module installations in the Energiewürfel building in Konstanz, Germany, (left) and the Ludesch Community Centre "town square" plaza in Vorarlberg, Austria (right). Photo Credit: Sunways AG

The Beit Havered building near Tel Aviv, Israel, has a photovoltaic façade composed of crystalline silicon glass with white digital printing on the surface. The printing provides a more traditional appearance while allowing the solar energy to pass through to the PV cells behind. The 608 m² installation is estimated to generate 1,938,623 kWh of electricity over 35 years, with avoided CO₂ emissions of 1,409 Tons of CO₂. The system payback period is less than 4 years.

The Beit Havered building's façade of c-Si PV glass with white digital printing on the surface provides a more traditional commercial/office building aesthetic. Photo Credit: Onyx Solar

The Paul Horn Arena in Tübingen, Germany, is comprised of PV modules designed to be both attractive and efficient power generators. The aesthetics take advantage of the emerald-green "fractured" multi-crystalline silicon cell appearance mounted within oversized white rectangular frames. The unobstructed, 530 m² installation receives continuous solar insolation throughout the day. The system generates 43.7 kWp of electricity.

The south façade of the Paul Horn Arena in Tübingen, Germany. Photo Credit: Sunways AG

The Life Sciences Building (LSB) at the University of Washington has a 650 m² 20% transparent amorphous silicon (a-Si) vertical fin BIPV installation on the southwest curtain wall. The photovoltaic fins generate 3.15 W/ft², and over their 35 year lifespan are estimated to provide 496,885 kWh of electricity with a CO₂ avoidance of 333 Tons of CO₂.

The southwest façade of the Life Sciences Building (left) and a close-up of the semi-transparent fins (right). Photo Credit: Onyx Solar

The Frank Gehry designed Novartis Campus building in Basel, Switzerland, exhibits the freeform potential of BIPV. The envelope contains a combination of dual-glass PV skylights and PV window modules with imbedded, perforated PV cells. The 1,300 m² PV installation provides 92 kWp of electricity.

The Novartis Campus building southern façade (left) and outward view from the interior (right) show that photovoltaic systems do not need to dominate a building's aesthetic to be effective. Photo Credit: Sunways AG

Relevant Codes and Standards

• IEEE 1547 Standard for Interconnecting Distributed Resources with Electric Power Systems
• Inflation Reduction Act of 2022 (IRA)  and the EPA summary
• International Code Council (ICC) 690.12
• NFPA 70 National Electrical Code (NEC) Article 690.12
• UL 1703 Standard for Flat-Plate Photovoltaic Modules and Panels
• UL 1741 Standard for Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy Resources

Publications

• Building-Integrated Photovoltaic Designs for Commercial and Institutional Structures: A Sourcebook for Architects 
• Building-Integrated Solar Technology, Roland Krippner (Ed.), Detail Business Information GmbH, Munich, DE, www.detail.de, ISBN 978-3-95553-362-5 (Print), ISBN 978-3-95553-363-2 (E-Book), ISBN 978-3-95553-364-9 (Bundle)
• The SwissTech Convention Center, Richter Dahl Rocha & Associés architects SA, Editions Favre SA, Lausanne, ISBN 978-2-8289-1480-6

Additional Resources

Websites

• Database of State Incentives for Renewables & Efficiency (DSIRE), provides a comprehensive list of federal, state, and local incentives that promote renewable energy and energy efficiency.
• DOE's EERE Solar Photovoltaics Technology Basics, gives a brief description of how the photovoltaic materials convert sunlight into electrical energy.
• National Center for Photovoltaics (NCPV), focuses on innovations in photovoltaic technology that drive industry growth in photovoltaic manufacturing nationwide. Formed by the U.S. Department of Energy (DOE) and based at NREL, the NCPV focuses on research and development and increasing U.S. competitiveness.
• North American Board of Certified Energy Practitioners (NABCEP), provides an industry certification of experienced photovoltaic installers. NABCEP was designed to raise industry standards and promote consumer confidence in photovoltaic and solar thermal system installations.
• Procuring Solar Energy: A Guide for Federal Facility Decision Makers , provides an overview for federal facility managers and their procurement terms, for the process of installing solar electric and solar thermal systems.
• Sandia National Laboratories, works with the U.S. Department of Energy, industry, and academia to improve the performance and reliability of photovoltaic technologies and grid integration.

Computer-Based PV Design and Sizing Tools

• HOMER—Hybrid Optimization Model for Electric Renewables (HOMER) is a design optimization model that determines the configuration, dispatch, and load management strategy that minimizes life-cycle costs.
• NREL's PVWatts calculator—Determines the energy production and cost savings of grid-connected photovoltaic energy systems throughout the world.
• PV F-Chart—Provides analysis and rough sizing of both grid-connected and stand-alone PV systems.
• PVFORM—Offers simulation of grid-connected and stand-alone systems, including economic analysis. Available from Sandia National Labs, Albuquerque, NM.
• TRNSYS—Simulation system for renewable energy applications; originally for solar thermal, now has extensions for PV and wind.

Other

• Solar-Estimate.org is a free public service offering solar estimating tools and is supported by the Department of Energy and the California Energy Commission.

Training Courses

• Solar energy courses in WBDG continuing education

Endnotes

¹ Onyx Solar, Products and Services.

² U.S. Energy Information Administration, Frequently Asked Questions (FAQS).

³ "Economic analysis of BIPV systems as a building envelope material for building skins in Europe", by Hassan Gholami and Harald Nils Røstvik; Department of Safety, Economics and Planning, University of Stavanger, Kjell Arholmsgate 41, 4036, Stavanger, Norway.

⁴ "Sustainability in Practice, Building and Running 343 Second Street, The Packard Foundation Headquarters", by Robert H. Knapp, Physics and Sustainable Design, Evergreen State College.

Introduction

A growing number of manufacturers of building materials and furnishings are leading the industry in moving toward improved product sustainability. To help achieve this mission, sustainability assessment standards have been developed across a broad range of product categories to assist manufacturers in identifying strategies and communicating improved performance. The standards often include relevant criteria across the product's life cycle, i.e. from growth phase of renewable materials, raw material extraction, manufacturing, use, and end-of-life management. Through multiple levels of achievement, many of these standards are providing an incentive for manufacturers to continue reducing the environmental impacts of their products and providing a way for designers and specifiers to distinguish among industry leaders.

Description

The purpose of sustainability assessment standards is to provide a thorough communication of information that is verifiable, accurate, and not misleading about the environmental and social aspects associated with the production and use of building materials and furnishings. Such communication is expected to encourage the demand for and supply of products that cause less stress on the environment and society, thereby stimulating the potential for market-driven continuous improvement. Private and public sector interests have encouraged manufacturers to improve the environmental performance of and provide environmental impact information on the products they produce.

These standards are intended to be science based, provide transparency, and offer credibility for manufacturers in making claims of environmental preferability and sustainability, and to harmonize the principles and procedures used to support such claims. These standards provide a practice for assessing the sustainability of building materials and furnishings. Sustainability-related information can inform a manufacturer's decisions about supply chain modifications, product(s) content changes, manufacturing adjustments, performance improvements, end-of-life options, and corporate governance, with the goal of producing more sustainable products.

Sustainability assessment standards also provide a means to track incremental changes to the products' sustainability profile. These standards are intended to provide a consistent framework in which to compare and assess the sustainable nature of different products that perform similar functions.

Trends in the criteria of sustainability assessment standards include:

• Multi-attribute assessment of the product/product category of interest
• Life-cycle based consideration of the product/product category of interest
• Science-based, verifiable criteria
• Assessment of corporate governance and social responsibility indicator reporting
• Product performance assessment as baseline criteria
• Consideration of relevant international criteria, or is adaptable to international markets

Most sustainability assessment standards have been designed, in part, to satisfy the following criteria:

• Product design, encouraging manufacturers to integrate environmental and life-cycle thinking into the product(s) design process.

• Product manufacturing, encouraging manufacturers to quantify the environmental impacts from their manufacturing, and then act to reduce or remove those impacts.

• Long-term value, encouraging manufacturers to maximize product(s) longevity.

• End of life management, ensuring that existing and new resilient flooring products can be collected, processed, recycled, and/or composted within the existing materials recycling infrastructure.

• Corporate governance, encouraging corporate social responsibility in the forms of providing a desirable workplace, being involved in the local community, and demonstrating financial health.

• Innovation, to give manufacturers the opportunity to be awarded points for exceptional performance above the requirements set forth in the standard.

ANSI Requirements for Voluntary Consensus Standards

An ANSI-accredited voluntary consensus standards body follows a process with the following attributes:

• Openness to all impacted stakeholders and interested parties;
• Balance of diverse interests and participation by all impacted stakeholders;
• Due process allowing for the expression of positions and their basis, and the consideration of all positions;
• A readily available and impartial appeals process;
• Consensus, which is defined as general agreement, but not necessarily unanimity, and includes process for attempting to resolve objections by interested parties, as long as all comments have been fairly considered, each objector is advised of the disposition of his or her objection(s) and the reason why, and the consensus body members are given the opportunity to change their votes after reviewing the comments

Certification

Once a sustainability assessment standard has been published there are several ways in which products can be certified as meeting the requirements contained in the standard including:

Self-Certification

A product manufacturer may choose to certify that its product meets the requirements in a standard to achieve a specified achievement level. They simply provide a statement or certificate stating the product meets the standard requirements. The value or strength of this type of certification is solely based on the reputation of the product manufacturer.

2nd Party Certification

An association, to which the product manufacturer belongs, provides the assurance for this certification. It is the responsibility of the association to monitor and assure the quality of the individual members to ensure the reputation of the product association.

3rd Party Certification

A third party provides the certification, which is completely independent from the product manufacturer, contractor, designer, and specifier. Third party certifications are the more trusted form of environmental conformance verification since they require the hiring of an outside auditing firm. Although they are the most expensive type of certification, third party certifications can be very helpful because they validate the product meets industry independent standards. They also provide assurance to specifiers, building owners, designers, and consumers that the product manufacturer's marketing claims are accurately stated.

Application

These standards are intended to be used primarily by product(s) manufacturers interested in understanding the sustainability performance of their product(s). Independent auditors, certification bodies, and environmental labeling organizations are also potential users of these standards for their use in supporting market-based environmental and sustainability claims. These standards may also be used by purchasers and consumers who wish to ensure that manufacturers are accurately declaring the sustainable nature of their products. These standards can be used where building materials and furnishings are being specified for green commercial, industrial, and residential buildings.

Additionally these standards can be used as part of government programs that identify products which exhibit reduced impacts on the environment.

The National Technology Transfer and Advancement Act of 1995 (NTTAA) directs federal agencies to use voluntary consensus standards, in lieu of government-unique standards, in procurement and regulatory activities, unless use of such standards would be inconsistent with applicable law or otherwise impractical. Office of Management and Budget (OMB) Circular A-119 implements the NTTAA and defines standards and voluntary consensus standards for the federal community. OMB A-119 does not establish a preference between consensus and non-consensus standards developed in the private sector. In general, A-119 provides broad discretion to individual agencies in determining if/how to make use of non-governmental standards. This provides agencies with the flexibility to select standards that best meet their needs.

Various laws and parts of the Federal Acquisition Regulation (FAR) require that agencies purchase environmentally sustainable products and services. All GSA employees are responsible for complying with the GSA Green Purchasing Plan (GPP) . The General Services Administration (GSA) currently references several sustainability standards in PBS-P100 Facilities Standards for the Public Buildings Service.

The Collaborative for High Performance Schools (CHPS) references several sustainability assessment standards in the Environmentally Preferable Products section of their Best Practices Manual.

The ICC-700 National Green Building Standard references several sustainability assessment standards in the Innovative Practices section. (See also Green Building Standards and Certification Systems.)

ISO Principles for Third-party Conformity Assessment Programs

Conformity assessment refers to the procedures and practices used to determine whether a product conforms to the requirements of a standard and/or ecolabeling program. In order to instill confidence among specifiers Type 1 independent third party certification programs developed in accordance with the principles of ISO 14024 have been established for a growing number of voluntary consensus product sustainability assessment standards. These certification programs are typically distinguished by adherence to the following principles:

• Independence in auditing processes and decision making
• Accessibility to interested parties
• Involvement of a balance of interests in management of the program
• Process for the management and resolution of complaints and appeals
• Accreditation as an independent third party certifier under ISO Guide 65 by ANSI.

Emerging Issues

EPA Efforts to Develop Guidelines for Selecting Product Environmental Performance Standards and Ecolabels for Federal Procurement

In the near future, the Environmental Protection Agency (EPA) plans to seek public comment on draft Guidelines intended to provide a transparent, fair, and consistent approach to using non-governmental product environmental performance standards and ecolabels in federal purchasing, consistent with federal standards policy and sustainable acquisition mandates. The draft Guidelines are being developed in response to requests via a wide variety of stakeholder engagement channels from manufacturers, environmental organizations, federal purchasers, and other stakeholders over the last several years.

Use of the Guidelines would facilitate an effective and efficient implementation of Section 2(h) of Executive Order (E.O) 13514 "Federal Leadership in Environmental, Energy, and Economic Performance" and Federal Acquisition Regulation (FAR) 23.103 which requires 95 percent of the government's applicable contract actions to be sustainable. Specifically, the Guidelines would provide clarity regarding the term "environmentally preferable" for purposes of the E.O.

Relevant Codes and Standards

• ANSI A138.1 Green Squared Specifications for Sustainable Ceramic Tiles, Glass Tiles and Tile Installation Materials 
• ANSI/BIFMA e3 Furniture Sustainability Standard 
• ANSI/NALFA LF 02 Laminate Flooring Sustainability Standard 
• NSF/ANSI 140 Sustainability Assessment for Carpet 
• NSF/ANSI 332 Sustainability Assessment for Resilient Floor Coverings 
• NSF/ANSI 336 Sustainability Assessment for Commercial Furnishings Fabric 
• NSF/ANSI 342 Sustainability Assessment for Wallcovering Products 
• NSF/ANSI 347 Sustainability Assessment for Single Ply Roofing Membranes 
• UL 100 Sustainability Assessment for Gypsum Board and Panel Products 
• UL 102 Sustainability Assessment for Swinging Door Leafs 

Additional Resources

Training Courses

Procurement courses in WBDG continuing education

Federal Agencies

• Executive Orders
  • Executive Order 13693, "Planning for Federal Sustainability in the Next Decade"
• Department of Defense
  • U.S. Army, U.S. Army Sustainability
  • U.S. Army—Army Corps of Engineers, EKO Fact Sheet
  • U.S. Navy—The U.S. Navy Sustainable Development section of WBDG
  • U.S. Air Force - AFCEC—Environmental Directorate-Sustainability
• Department of Energy
  • Building Technologies Program Office, Office of Energy Efficiency and Renewable Energy (EERE)
  • Commercial Buildings Integration, Office of Energy Efficiency and Renewable Energy (EERE)
  • Building Performance Database (BPD), Office of Energy Efficiency and Renewable Energy (EERE)
  • Federal Energy Management Program (FEMP), Office of Energy Efficiency and Renewable Energy (EERE)
  • FEMP Sustainable Federal Buildings and Campuses
  • FEMP Interagency Sustainability Working Group
• Department of Veterans Affairs
  • Sustainable Design, Office of Construction and Facilities Management (CFM)
• Environmental Protection Agency
  • Green Building
  • Greening EPA
• General Services Administration
  • Greening Federal Buildings
  • Sustainable Design
  • Climate Action and Sustainability
  • Sustainable Facilities Tool
• NASA
  • Sustainability

Introduction

Natural and manmade hazardous events can impose a devastating cost upon society. As Figure 1 shows, the costs of some of these disasters in the United States alone can be staggering. Stakeholders of civil infrastructure have a vested interest in reducing these costs by improving and maintaining operational and physical performance.

Figure 1: Damages from recent natural disasters in the US. The name of the disaster follows the year of occurrence. Source EM-DAT (2014).

Throughout history, infrastructure resilience has been defined in numerous ways, the most widely used and most objective is by the National Infrastructure Advisory Council (NIAC*) (2009), which states:

"Infrastructure resilience is the ability to reduce the magnitude and/or duration of disruptive events. The effectiveness of a resilient infrastructure or enterprise depends upon its ability to anticipate, absorb, adapt to, and/or rapidly recover from a potentially disruptive event."

No city is immune to challenges, whether natural or manmade, and given the world's growing population, more people than ever are in the potential path of catastrophe. Fortunately, cities can become resilient and withstand shock and stress. As conditions change over time, cities that are resilient can evolve in the face of disaster and stop failure from rippling through systems; they can reestablish function quickly and avoid long-term disruptions.

This resource page explores different aspects of resilience management, to control and help reduce the rapidly increasing costs of manmade and natural hazards and ensure that civil infrastructure exhibits a high degree of resilience. A definition of resilience that incorporates using four components—robustness, resourcefulness, recovery and redundancy—is presented and its manifestation in building systems is covered.

Stakeholders of buildings stand to benefit from resilience management. Businesses locate where they can rely on critical infrastructure. Communities that become resilient will increasingly attract businesses because executives know they can rely on the services and workforce availability, even in the face of disruptive events.

Natural and manmade hazardous events are unpredictable, but they are still inevitable and impose a devastating cost to civil infrastructure. By improving and maintaining the operational and physical performance of our nation's building stock, strategies for resilience can be developed.

When planning and designing buildings, it is appropriate to try to mitigate the potential of the spiraling cost of operational failures by opting for more resilient performance through well-thought-out investments in better planning and designs. It no longer makes sense to wait until after a crisis to implement resilience efforts. Resiliency strategies for buildings should be discussed and implemented now, so there is a greater chance of increased performance, not only today but for the future, benefiting all buildings stakeholders.

Description

Components of Building Resilience

The 4–Rs

The NIAC (2009) determined that resilience can be characterized by four key features:

• Robustness: the ability to maintain critical operations and functions in the face of crisis. This includes the building itself, the design of the infrastructure (office buildings, power generation, distribution structures, bridges, dams, levees), or in system redundancy and substitution (transportation, power grid, communications networks).

• Resourcefulness: the ability to skillfully prepare for, respond to and manage a crisis or disruption as it unfolds. This includes identifying courses of action and business continuity planning; training; supply chain management; prioritizing actions to control and mitigate damage; and effectively communicating decisions.

• Rapid recovery: the ability to return to and/or reconstitute normal operations as quickly and efficiently as possible after a disruption. Components of rapid recovery include carefully drafted contingency plans, competent emergency operations, and the means to get the right people and resources to the right places.

• Redundancy, is proposed as another key feature, which mean that there are back-up resources to support the originals in case of failure that should also be considered when planning for resilience.

These four resilience features are simply called the 4Rs. Resilience is multidisciplinary and needs the cooperation of different disciplines for successful outcome. Without multidisciplinary cooperation and contributions, there cannot be successful or efficient resilient infrastructure.

A beneficial illustration of resilience was introduced first by Mary Ellen Hynes (2001) and then by Bruneau et. al (2003). Figure 3 shows graphically how to objectively estimate the resilience of an asset or community by utilizing resilience charts. The illustration shows how an undesirable event might affect two assets (or communities). The operations of asset (or community) "A" will immediately lose some operational quality, then start recovering until returning back to full operational quality. As for asset (or community) "B," it will lose much of its operational quality when subjected to the same undesirable event. It will recover but on a much slower pace than asset "A." Thus, it is concluded that "A" is more resilient than "B." The area under the curve describes the time-operational quality behavior of the asset or community to objectively assess the resilience of the asset or community.

Figure 2: Resilience definition in the time-operational quality space (showing the Resilience Chart).

Figure 3: Comparison between the Resilience of two Assets (or communities) using Resilience Charts.

Asset (Building) Resilience and Community Resilience

One of the objectives is to clarify distinctions and relationships between three of the emerging paradigms: risk, resilience, and sustainability. First, risk is expressed as the relationship between a particular hazard (or threat) that might degrade the performance of the infrastructure under consideration and the consequences that might result from a degradation of performance (Gutteling and Wiegman 1996, FEMA 2005, and NRC 2010). Most professional industries, such as engineering, finance, insurance and medicine, adopt a variant of this particular definition of risk (Gutteling and Wiegman 1996). In the building/infrastructure community, FEMA (2005) uses an objective risk definition that states:

Risk rating = function (Consequences, Threat, Vulnerability — C, T, V)

The type of risk function also depends on the desired degree of complexity of risk analysis.

It was established earlier that a reasonable resilience definition relates resilience to robustness, resourcefulness, recovery, and redundancy (the 4Rs). It can be shown that the 4Rs can be recast as a subset of C, T, V. Ettouney and Alampalli, 2012, proposed a relationship similar to that shown in Table 1. These relationships are illustrated in Figure 4.

Table 1 - Relationships Between Risk and Resilience

Figure 4: Risk, Resilience, Sustainability Interrelationships

Resilience Management-Based Building Designs

There is an essential distinction between asset resilience and community resilience. As the label implies, asset resilience is the resilience of a single asset. For immediate purposes, an asset is considered to be an individual building. Note that other types of assets are also feasible such as bridges, mass transit stations, transmission towers, or tunnels. DHS (2009) and the American Society of Civil Engineers (ASCE) Report Card (2013), each contain a comprehensive list of types of assets.

Asset resilience is described using the resilience definition above with the 4Rs. Within an asset, different parameters (sometimes referred to as considerations) control asset resilience. These parameters can be categorized as components of one or more of the 4Rs. Table 2 shows a simplified example of building components and categorizations in an asset resilience setting. Note that Columns fit in more than one resilience component (robustness and redundancy). In addition to the categorizations of Table 2, a functional diagram, called a network or a graph, needs to be established. This network shows dependencies of different parameters. The dependencies are expressed by arrows from the controlling parameter to the dependent parameter. If there is no obvious dependence between two linked parameters, then a simple line connecting the two parameters is used. Figure 5 shows a simple network for an asset resilience of a tall building. Capturing important parameters (both operational and physical) as well as their interdependencies as shown in Table 2 and 5 are essential first steps for achieving successful asset resilience management.

Table 2 - Resilience Example of Individual Building as an Asset

Figure 5: Asset Resilience Links for Resilience Management (Simplified Tall Building Example)

Turning attention to community resilience—as the name implies, a community is comprised of several assets (nodes) that are interconnected via links that may be assets themselves. The nodes and links constitute a community's network. Community resilience is dependent on the resilience of the network's individual asset components (both nodes and links). As an essential step of community resilience management, a greater understanding of the resilience of nodes and links is needed. In addition, community resilience will depend on the topology of the network and how different nodes are linked together.

The size of the community is completely subjective. A community could be a simple campus comprising a small number of buildings (such as a small hospital or college). A community could be a transportation network, a small town, a region, a state, or even a whole country. Each of the 4Rs of community resilience is a function of all of the 4Rs of its nodes and links as well as the topology of the network. Figure 6 shows a simple resilience network for a small community.

Figure 6: Community Network for Resilience Management

Life Cycle and Cost/Benefit Considerations in Resilience-Based Designs

Incorporating resilience into new building designs, existing building retrofits, and ongoing building operations can carry significant costs. To justify investments in resilience it is imperative to evaluate the cost/benefit relationship of the investments over the full life cycle of the facility. To evaluate increasing resilience, it is necessary to identify performance (or for safety and security objectives, protection) levels and their impact on reducing risk and increasing resilience. With performance/protection levels identified, the costs associated with achieving the performance/protection identified can be calculated and used to evaluate the benefits of higher resilience. The relationships between functional performance, risk, resilience, and cost are identified in Figure 7.

Figure 7: Risk, Resilience, and Performance Relationships

Establishing the tradeoffs between performance and cost requires evaluating the relationships between the cost of providing building systems, their performance over the life of the facility, including response to undesirable events and the interrelationships between systems and performances. Traditional first-cost estimating approaches cannot effectively handle these evaluations. Evaluating Total Cost of Ownership (TCO) is a more effective way to analyze all of the cost factors identified in Figure 7. TCO is calculated by establishing capital cost for the building or improvement and then adding to it the discounted costs of future expenses (operations, maintenance, recovery) to arrive at a TCO. TCO can then be compared for different configurations to perform a cost analysis of the benefits of increasing performance to increase resilience. This methodology is implemented in a DHS project entitled Owners Performance Requirements for Building Envelopes. More information about the approach and access to a tool that implements it is available at www.oprtool.org.

Short-Term Versus Long-Term Resilience Planning

It has been shown that long-term planning can help immensely in cost savings (see FEMA [1996] and MMC [2005]). An objective way to accommodate such long-term cost savings is by following a reasonable resilience management procedure during planning, design, and throughout the life span of the building. Some details of resilience management components are offered in the Resilience Assessment and Resilience Acceptance information below.

Existing Structures Versus New Buildings

The options for enhanced resilience available to existing buildings are more limited than for new building construction. For existing buildings, an appraisal will help determine whether an economical upgrade may be constructed without adversely affecting the existing structure and whether the upgrade is economically feasible. This will help determine whether the risks are worth taking and whether the building is suitable for a proposed function. The structural engineer must evaluate both the risk and the economic feasibility.

If an upgrade is found to be worth pursuing, the engineer must determine the as-built building information, such as the type and arrangement of existing vertical and lateral-force-resisting systems, and the nonstructural components that either affect the structure's stiffness, strength, or the continuity of the structural load path. The as-built information primarily focuses on the load-resisting components, which include structural and nonstructural components that participate in resisting gravity loads, whether or not they were intended to do so by the original designers. This information typically identifies potential discontinuities in the load path, weak links, irregularities, inadequate strength, and stiffness.

The available construction documents may provide primary gravity and lateral-force-resisting elements, critical components, and connections. In the absence of a complete set of building drawings, the design team must perform a thorough investigation of the building. This typically requires the examination of concrete, reinforcing steel, and connector steel samples for physical condition. Generally, mechanical properties for both concrete and reinforcing steel can be established from combined core and specimen sampling at similar locations, followed by laboratory testing. Core drilling should minimize damage of the existing reinforcing steel as much as is practicable. Nominal material properties, or properties specified in construction documents, shall be taken as lower-bound material properties.

Structural steel components constructed after 1900 shall be classified based on ASTM specification and material grade and, if applicable, shape group. Lower-bound material properties may be taken for known steel materials or may be based on tests where the material grade or specified value is not known. The carbon equivalent of the existing components must be determined to establish weldability of the material.

The K factor is typically used to express the confidence with which the properties of the building components are known. The K factor is based on original construction documents or condition assessments, including destructive or nondestructive testing of representative components.

Resilience Assessment

The first component in resilience management is to assess the resilience level of either the asset or the community of interest. Since resilience is a special representation of risk, it is natural to utilize risk assessment methods when trying to assess resilience. Some of the methods for assessing risk are based on subjective processes (Gutteling and Wiegman 1996), while others are based on objective processes (DHS 2011b, 2011c, and 2011d). There are detailed relative and absolute risk assessment methods available (Ettouney and Alampalli 2012a and 2012b). There are even probabilistic or deterministic risk assessment methods (Fenton and Neil 2013).

It is possible to use any or all of these methods for resilience assessment. Since resilience is based on the 4Rs, the parameters of each of the 4Rs in each asset need to be determined, and the desired methodology (which can be borrowed from any desired risk methodology) must be followed. After that, computing an objective or subjective resilience rating can be achieved in a simple and accurate manner. DHS 2011b, 2011c, and 2011d followed these procedures to compute resilience ratings for tunnels, subway stations, and buildings.

Assessing community and network resilience can be achieved using the resilience ratings from different assets and links between those assets in a network setting.

Resilience Acceptance

Setting acceptance thresholds is perhaps the most difficult step in asset (or community) management. Traditionally, a prescribed acceptance threshold was adopted in civil infrastructure projects and based on a reasonable, yet subjective, probabilistic non-exceedance¹ value (Ettouney and Alampalli 2015a and 2015b). (Note that an example of probabilistic non-exceedance is stating that there is a 95 percent probability that the next flood in a particular area will not exceed a particular damaging level.) This practice was reasonable enough for its time, since civil infrastructure projects were mostly based on ensuring safety. With the advent of risk-based paradigms, where project decisions are based on safety as well as cost (both life-cycle costs and initial capital expenditures), setting risk acceptance thresholds has become more difficult to define. The same holds true for resilience. Objectively, what is a reasonable acceptance threshold for resilience of a particular asset or particular community? The answer to this question is as important as defining and assessing resilience. For without setting a threshold, resilience improvement projects could be either unnecessarily costly or result in reduced performance (see Figure 8). At the time of this writing, there were few objective methods available for setting reasonable resilience acceptance thresholds but some general suggestions can be made regarding methodologies for setting resilience thresholds. A simple approach is to try to set the acceptance threshold so as to minimize total costs, as illustrated in Figure 8.

Figure 8: Business Case for Resilience Acceptance

Additional Resources

Publications

• "A Framework to Qualitatively Assess and Enhance the Seismic Resilience of Communities" by Bruneau, M, Chang, S, Eguchi, R., O'Rourke, T., Reinhorn, A., Shinozuka, M., Tierney, K., Wallace, W., Winterfelt, D. Earthquake Spectra Journal Vol. 19, No. 4: 733-752, Earthquake Engineering Research Institute, 2003.
• ASEC Report Card for America's Infrastructure by American Society of Civil Engineers, Reston, VA: ASCE 2013.
• Costs and Benefits of Natural Hazard Mitigation by Federal Emergency Management Agency Report, Washington, DC: FEMA, 1996./li>
• Critical Infrastructure Resilience Final Report and Recommendations by National Infrastructure Advisory Council (NIAC), Washington, DC: NIAC, 2009.
• EM-DAT: The OFDA/CRED International Disaster Database by Université Catholique de Louvain. Brussels, Belgium: EM-DAT, accessed on April 2014.
• Exploring Risk Communications by Gutteling, J. and Wiegman, O. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1996.
• High Performance Based Design for the Building Envelope: A Resilience Application Project Report, Building and Infrastructure Protection Series, Washington, DC: DHS 2011.
• Infrastructure Health in Civil Engineering: Applications and Management by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
• Infrastructure Health in Civil Engineering: Theory and Components by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
• Integrated Rapid Visual Screening of Buildings, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Integrated Rapid Visual Screening of Mass Transit Stations, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Integrated Rapid Visual Screening of Tunnels, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Multihazard Considerations in Civil Infrastructure by Ettouney & Alampalli. Boca Raton, FL: CRC Press, 2016.
• National Infrastructure Protection Plan by Department of Homeland Security, Washington, DC: DHS, 2009.
• Natural Hazards Mitigation Saves: An Independent Study to Assess the Future Savings from Mitigation Activities: Volume 1 - Findings, Conclusions, and Recommendations by National Institute of Building Sciences Report, Washington, DC: MMC, 2005.
• Personal Communications by Hynes, Mary Ellen. Vicksburg, MS: 2001.
• Review of the Department of Homeland Security's Approach to Risk Analysis, National Academic Press, Washington, DC: NRC 2010.
• Risk Assessment: A How-To Guide to Mitigate Terrorist Attacks, Risk Management Series, FEMA 452 by Federal Emergency Management Agency, Washington, DC: FEMA, 2005.
• Risk Assessment and Decision Analysis with Bayesian Networks by Fenton, N., and Neil, M. CRC Press, Boca Raton, FL: 2013.
• Risk Management in Civil Infrastructure by Ettouney & Alampalli. CRC Press, Boca Raton, FL: 2016a.

Footnotes

¹ [An example of probabilistic non-exceedance is stating that there is a 95% probability that the next flood in a particular area will not exceed particular damaging level.]

Introduction

Security design and access control is more than bars on windows, a security guard booth, a camera, or a wall. Crime prevention involves the systematic integration of design, technology, and operation for the protection of three critical assets-people, information, and property. Protection of these assets is a concern and should be considered throughout the design and construction process.

The most efficient, least expensive way to provide security is during the design process. Designers who are called on to address security and crime concerns must be able to determine security requirements, must know security technology, and must understand the architectural implications of security needs.

The process of designing security into architecture is known as "crime prevention through environmental design" (CPTED). It involves designing the built environment to reduce the opportunity for, and fear of, stranger-to-stranger predatory crime. This approach to security design is different from traditional crime prevention practice, which focuses on denying access to a crime target with barrier techniques, such as locks, alarms, fences, and gates. CPTED takes advantage of opportunities for natural access control, surveillance, and territorial reinforcement. It is possible for natural and normal uses of the environment to meet the same security goals as physical and technical protection methods.

CPTED strategies are implemented by:

• Electronic methods: Electronic access and intrusion detection, electronic surveillance, electronic detection, and alarm and electronic monitoring and control
• Architectural methods: Architectural design and layout, site planning and landscaping, signage, and circulation control
• Organizational methods: Manpower, police, security guards, and neighborhood watch programs

CPTED Strategies All images courtesy of Randall I. Atlas

CPTED Concepts

Concepts involved in crime prevention through environmental design are described below.

Defensible Space

Oscar Newman coined the expression "defensible space" as a term for a range of mechanisms, real and symbolic barriers, strongly defined areas of influence, and improved opportunities for surveillance that combine to bring the environment under the control of its residents.

Natural Access Control

Natural access control involves decreasing opportunities for crime by denying access to crime targets and creating a perception of risk in offenders. It is accomplished by designing streets, sidewalks, entrances, and neighborhood gateways to mark public routes, and by using structural elements to discourage access to private areas.

Natural Surveillance

A design concept intended to make intruders easily observable, natural surveillance is promoted by features that maximize visibility of people, parking areas, and entrances. Examples are doors and windows that look onto streets and parking areas, pedestrian-friendly sidewalks and streets, front porches, and adequate nighttime lighting.

Territorial Reinforcement

Physical design can create or extend a sphere of influence. In this setting, users develop a sense of territorial control, while potential offenders perceive this control and are discouraged from their criminal intentions. Territorial reinforcement is promoted by features that define property lines and distinguish private spaces from public spaces, such as landscape plantings, pavement design, gateway treatments, and fences.

Management and Maintenance

It is important to maintain neighborhoods and residences, and keep security components in good working order. Equipment and materials used in a dwelling should be designed or selected with safety and security in mind.

Legitimate Activity Support

Legitimate activity for a space or dwelling is encouraged through the use of natural surveillance and lighting, and architectural design that clearly defines the purpose of the structure or space. Crime prevention and design strategies can discourage illegal activity and protect a property from chronic problem activity.

Security layering of spaces

Strategies

Designing CPTED and security features into buildings and neighborhoods can reduce opportunities for, and vulnerability to, criminal behavior and help create a sense of community. The goal is to create safe places through limited access to properties, good surveillance, and a sense of ownership and responsibility.

Natural Access Control and Surveillance

• Use walkways and landscaping to direct visitors to the proper entrance and away from private areas.
• All doorways that open to the outside as well as sidewalks and all areas of the yard should be well lit.
• Make the front door at least partially visible from the street and clearly visible from the driveway or parking lot.
• Windows on all sides of the building should provide full views of the property. The driveway should be visible from the front or back door and from at least one window.
• Properly maintained landscaping should provide good views to and from the building.

Territorial Reinforcement

• Entryways or vestibules create a transitional area between the street and the building.
• Define property lines and private areas with plantings, pavement treatments, or fences.
• The street address should be clearly visible from the street, with numbers a minimum of 5 in. high and made of nonreflective material.

Crime Prevention through Environmental Design - Plan View

Subdivisions and Office Parks

Natural Access Control

• Limit access to the subdivision without completely disconnecting it from neighboring areas. However, try to design streets to discourage cut-through traffic.
• Paving treatments, plantings, and architectural design features such as columned gateways can guide visitors away from private areas.
• Locate walkways where they can direct pedestrian traffic and remain unobscured.

Natural Surveillance

• Landscaping should not create blind spots or hiding places.
• Locate open green spaces and recreational areas so they can be observed from nearby houses.
• Use pedestrian-scale street lighting in areas with high pedestrian traffic.

Territorial Reinforcement

• Design lots, streets, and houses to encourage interaction between neighbors.
• Accent entrances with changes in street elevation, different paving materials, and other design features.
• Clearly identify residences with street address numbers that are a minimum of 5 in. high and are well lit at night.
• Property lines should be defined with post-and-pillar fencing, gates, and plantings to direct pedestrian traffic.
• All parking should be assigned.

Multi-Family Dwellings

Natural Access Control

• Balcony railings should never be made of a solid, opaque material or be more than 42 in. high.
• Define parking lot entrances with curbs, landscaping, and/or architectural design; block dead-end areas with a fence or gate.
• Common building entrances should have locks that automatically lock when the door closes.
• Limit access to the building to no more than two points.

Natural Surveillance

Territorial Reinforcement

• Define property lines with landscaping or post-and-pillar fencing, but keep shrubbery and fences low to allow visibility from the street.
• Accent building entrances with architectural elements and lighting and/or landscape features.
• Doorknobs should be 40 in. from window panes.
• Clearly identify all buildings and residential units with well-lit address numbers a minimum of 5 in. high.
• Common doorways should have windows and be key-controlled by residents.
• Locate mailboxes next to the appropriate residences.

Crime Prevention Through Environmental Design - Sectional View

Additional Resources

Publications

• "A Framework to Qualitatively Assess and Enhance the Seismic Resilience of Communities" by Bruneau, M, Chang, S, Eguchi, R., O'Rourke, T., Reinhorn, A., Shinozuka, M., Tierney, K., Wallace, W., Winterfelt, D. Earthquake Spectra Journal Vol. 19, No. 4: 733-752, Earthquake Engineering Research Institute, 2003.
• ASEC Report Card for America's Infrastructure by American Society of Civil Engineers, Reston, VA: ASCE 2013.
• Costs and Benefits of Natural Hazard Mitigation by Federal Emergency Management Agency Report, Washington, DC: FEMA, 1996./li>
• Critical Infrastructure Resilience Final Report and Recommendations by National Infrastructure Advisory Council (NIAC), Washington, DC: NIAC, 2009.
• EM-DAT: The OFDA/CRED International Disaster Database by Université Catholique de Louvain. Brussels, Belgium: EM-DAT, accessed on April 2014.
• Exploring Risk Communications by Gutteling, J. and Wiegman, O. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1996.
• High Performance Based Design for the Building Envelope: A Resilience Application Project Report, Building and Infrastructure Protection Series, Washington, DC: DHS 2011.
• Infrastructure Health in Civil Engineering: Applications and Management by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
• Infrastructure Health in Civil Engineering: Theory and Components by Ettouney and Alampalli. Boca Raton, FL: CRC Press, 2012.
• Integrated Rapid Visual Screening of Buildings, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Integrated Rapid Visual Screening of Mass Transit Stations, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Integrated Rapid Visual Screening of Tunnels, Building and Infrastructure Protection Series, Washington, DC: DHS, 2011.
• Multihazard Considerations in Civil Infrastructure by Ettouney & Alampalli. Boca Raton, FL: CRC Press, 2016.
• National Infrastructure Protection Plan by Department of Homeland Security, Washington, DC: DHS, 2009.
• Natural Hazards Mitigation Saves: An Independent Study to Assess the Future Savings from Mitigation Activities: Volume 1 - Findings, Conclusions, and Recommendations by National Institute of Building Sciences Report, Washington, DC: MMC, 2005.
• Personal Communications by Hynes, Mary Ellen. Vicksburg, MS: 2001.
• Review of the Department of Homeland Security's Approach to Risk Analysis, National Academic Press, Washington, DC: NRC 2010.
• Risk Assessment: A How-To Guide to Mitigate Terrorist Attacks, Risk Management Series, FEMA 452 by Federal Emergency Management Agency, Washington, DC: FEMA, 2005.
• Risk Assessment and Decision Analysis with Bayesian Networks by Fenton, N., and Neil, M. CRC Press, Boca Raton, FL: 2013.
• Risk Management in Civil Infrastructure by Ettouney & Alampalli. CRC Press, Boca Raton, FL: 2016a.

Introduction

This resource page is the first of a series on relevant topics in building science. It is aimed at explaining the key concepts involved in building science, as well as the relationship of this discipline to the architecture / engineering / construction (AEC) industry. It focuses on the systems approach to building technology and the utility of building science to advance the high-performance building agenda.

It should be recognized that prior to the introduction of the systems approach to the discipline of building science, most of research and practice dealt with construction materials and components. The consideration of the entire building system, or in some instances sub-systems, did not emerge until the limits of a less holistic approach became painfully obvious in the form of building defects and failures.

A great deal of research and development toward the advancement of the systems approach remains to be accomplished. Despite their limitations, the system models that have been adopted by modern building science have delivered an overwhelming improvement in the health, safety, and durability of buildings. For this reason, more than any other, building science is now recognized in most developed countries as the core of technical training for architects, explaining why buildings work, why buildings fail, and how to avoid the latter without compromising the artistic, cultural, and environmental qualities of the architectural artifact.

Description

Building Science Defined

Building science is a field of knowledge that draws upon physics, chemistry, engineering, architecture, and the life sciences. Understanding the physical behavior of the building as a system and how this impacts energy efficiency, durability, comfort and indoor air quality is essential to innovating high-performance buildings. Modern building science attempts to work with models of the building as a system, and to apply empirical techniques to the effective solution of design problems.

Neil Hutcheon, the famous Canadian building scientist, defined building science as "a term now widely used, for want of a better one, to describe the growing body of knowledge about the relevant physical science and its application."ⁱ

More specifically, contemporary building science is a broad discipline that is concerned with the full life cycle of buildings, including:

• policy (codes and standards);
• planning;
• design;
• construction;
• commissioning;
• facilities management;
• forensics and rehabilitation;
• restoration and retrofit;
• preservation and conservation; and
• demolition (deconstruction) and recycling.

The disciplinary involvement in contemporary building science ranges from the physical and engineering sciences, to economics, political science, behavioral sciences, life sciences, and architecture.ⁱⁱ

The importance of contemporary building science is often fully appreciated after the occurrence of building performance problems, or worse, after failures, rather than at the planning and design stage of building projects. For this reason, contemporary building science has taken on greater importance in response to an increasing trend of innovative departures from traditional building practices based on successful past precedents.

Innovation is not a trial and error process that relies on gradually refining past precedents. It is usually a significant departure from normative practices and relies on the scientific method to advance its agenda. Modern building science, as it is known today, was born of innovation - more correctly, because of the large number of failures encountered when building designers attempted to innovate without applying building science principles. There was no need for building science when only successful precedents were copied and handed down from one generation to the next, but there was also no advancement toward high-performance buildings within traditional building practices.

Building System Theory

Modern systems theory is an expansive body of knowledge with many branches. It is not possible to deal with the full range of theories within these resource pages, but consider these concepts of a system.ⁱⁱⁱ

A system is an integrated assembly of interacting elements, designed to carry out cooperatively a predetermined function. [Gibson 1960]

A system is an integrated network of interacting elements, receiving certain inputs and producing certain outputs, given certain constraints. [Chappelle 1966]

Systems theory, at its fundamental level, is a belief that the world is made up of set(s) of interacting components, and that those sets of interacting components have properties, when viewed as a whole, that do not exist within any of the smaller units. [Allen 1996]

A systems approach is essentially:

• A way of organizing observations;
• A way of thinking about related objects and processes;
• A way of talking about (labeling) the parts (components) of a system; and
• An outcome from systematically considering systemic phenomena.

Systems thinking is an important part of building science because it helps simplify problems by classifying them according to common types. There exist millions of buildings and their diversity would be overwhelming were it not for the systems approach. This approach is derived from general systems theory and the basic characteristics common to all systems are important to keep in mind when applying building science.

• Boundaries and Boundary Criteria—Many people believe that a building system ends at the outer surface of its enclosure, in some cases at the property line. But in reality, the building system extends to the outer reaches of what it impacts, and what impacts the building. Basement flooding due to municipal sewer surcharge is an example of the building's plumbing system extending to the local municipal infrastructure services.

• Flows and Storage—Inhabitants, energy, water, sewage, and data are examples of the flows and storage characteristics of the building as a system. Occupant behavior is among the most difficult flows to accurately predict in energy models.

• Transformations—Buildings age and they are modified by their users, not always in a beneficial way. It is desirable from a life cycle perspective to design buildings that can adapt and adopt new technologies to improve their performance and minimize functional obsolescence.

• Spatial and Temporal Hierarchies—Passive survivability and safe/secure building design are premised on achieving spatial and temporal resilience such that the vital functions are maintained both in day-to-day operations and under extreme conditions such as natural and man-made disasters.

• Feedback and Control Loops—Buildings are prosthetic extensions of the human body and as such rely on many forms of cybernetics to control the indoor environment and maintain safety and security.

Each of the above characteristics vary in importance, depending on the type of building being designed and its intended use. Building science specialization is often needed to deal with particular aspects of these characteristics (e.g., energy modeling, flood proofing, durability, indoor air quality, blast resistance, etc.). But in all cases, the fundamental understanding of how these characteristics interact may be derived from the building as a system model.

The Building as a System

The idea of the building as a system springs from modern systems theory and the application of building science principles to building behavior and performance.

The building as a system concept is a relatively new development in building science. It resulted directly from the introduction of a systems approach, to building science practice, starting in the 1960s. As innovation increasingly became the means to achieving new forms of architectural expression in the 20th century, analysis and review of building failures indicated that traditional approaches to design were inadequate. This was due to inappropriate adaptations of successful past precedents, or an unknowingly narrow analysis at the building component level for radical departures from technical norms. In both cases the behavior of the whole system was not considered.

The building as a system approach, as depicted in Figure 1, requires designers to explicitly and consciously consider the interactions between the primary elements comprising the system:

• Building enclosure (building envelope system);
• Inhabitants (humans, animals, and/or plants, etc.);
• Building services (electrical/mechanical systems);
• Site, with its landscape and services infrastructure; and
• External environment (weather and micro-climate).

Harmonization of these elements is the key to well-performing buildings.

Figure 1. The building as a system model.

Returning to the highly specialized nature of contemporary building science, it is recognized that a large number of materials, components, equipment, and assemblies must be properly integrated to achieve a high-performance building. At the same time, it must be appreciated that most performance problems involve the building enclosure, which also represents the primary passive environmental control system. In view of these considerations, this Resource Page is largely focused on the building science underlying building enclosures and how they are influenced by climate and weather. A comprehensive listing of design parameters may be found in the Resource Page on Building Enclosure Design Principles and Strategies.

Figure 2. Physical mechanisms driving the behavior of the building as a system.

Recognizing that the physical forces affecting structural integrity must always be adequately resolved, there remain four primary physical mechanisms associated with climate and weather that drive the behavior of the building as a system in terms of its role as a moderator of the indoor environment (see Figure 2):

• Heat Flow - the conductive, convective, and radiative flow of heat;

• Air Flow - the air flow across and within the building enclosure due to air leakage and ventilation;

• Moisture Flow - the flow of water and vapor across and within the building enclosure; and

• Solar Radiation - the influence of insulation on the opaque and transparent enclosure components.

In the building as a system, all of these physical mechanisms are occurring in various combinations at various times. During cold periods, heat and warm moist air escape through leaks in the building enclosure. To compensate, the heating system must supply the amount of heat being lost, and to replace the lost moisture, the indoor air must be humidified for occupant health and comfort. During hot periods, heat and warm moist air are driven into the building and the HVAC system must cool and dehumidify. Under all conditions, the building enclosure must manage the heat, air, and moisture flows. The occupants can exert as great an influence as the climate through their activities. This explains why a building may be very fit for one occupancy (e.g., warehouse or factory), but then experience problems when the occupancy changes (e.g., residential or institutional). Problems occur when the balance of moisture, heat, and air flows is disturbed beyond the performance thresholds of the building as a system.

The key to the fitness of a building is the balanced control of these physical mechanisms, so that durability, comfort, energy efficiency, indoor air quality, health, and safety are not compromised.

Building Performance

The term "performance" may be defined as the level of service provided by a building material, component, or system, in relation to an intended, or expected, threshold or quality.

For example, the structural performance of a building may be judged in terms of its resistance to dead, live, soil, wind, hydrostatic, and seismic loads as prescribed by applicable codes. Within the established thresholds for these loads, the structure would be required to behave adequately according to expectations in terms of strength, durability, deflections, and vibrations.

When the intended or expected level of performance is not achieved, the resultant behavior is termed a "failure" which must not be confused with the term "defect", a minor damage or blemish which has no immediate or significant impact on performance, and which may be suitably repaired.

An important contribution of building science is the quantification of performance parameters such that many of these can be predicted at the design stage, and assessed / confirmed after the building is occupied and operational. This preoccupation with prediction and validation has led to the appreciation of the need for a systems approach, as building scientists grapple with issues such as indoor air quality and sustainable buildings.

The significant thing to remember about inadequate building performance is that it results in the vast majority of litigation, and the application of building science via the systems approach is among the more effective preventive measures against failures and defects. It is also a highly useful diagnostic tool when assessing the condition of existing buildings that are candidates for restoration and retrofit. In order to deploy the systems approach in the design and assessment of buildings, it is first necessary to establish a framework of performance requirements. The section which follows deals with the ongoing development of such a framework based on the pioneering work of the late Neil Hutcheon, former Director of the Division of Building Research at the National Research Council Canada.^iv Figure 3 depicts a hierarchy of performance requirements derived from building science principles.^v

Figure 3. Building science hierarchy of performance requirements.

To borrow from mathematical terminology, building science is a necessary but insufficient condition for great architecture. However, its pivotal supporting role cannot be underestimated in importance. The vast majority of litigation between parties to construction projects involves the inadequate performance of building elements that are intended to provide firmness and commodity. Inferior delight is still only punishable by the rebukes of peers and critics, and has so far eluded the grasp of litigation and legislation.

The concept of a building performance framework is intended to explicitly represent:

• External and internal conditions affecting a building system (e.g., climate, weather, site, soils, occupancy, and indoor climate class);
• Parts and inter-relationships comprising a building system (e.g., the behavior of materials, components, equipment and sub-systems);
• Parameters or indicators defining acceptable performance (e.g., aesthetics, health and safety, economy, sustainability, etc.); and
• Methods, tools, and techniques for designing and analyzing performance according to the parameters, inter-relationships and conditions cited above.

Context for Contemporary Building Performance Objectives

Appropriate building performance objectives involve numerous interfaces between the building, its occupants, and the natural and built environment as depicted in Figure 4. Some of these interfaces cannot be regulated (e.g., climate, weather, human physiology, etc.), while others may be manipulated within some prescribed range (e.g., energy efficiency, affordability, etc.). The terms of reference for the regulated aspects of buildings remain in a constant state of flux, as evidenced by the many changes associated with each development cycle of building codes and standards. And the context for building performance in relation to the environment, the economy, and occupant expectations has also changed appreciably in developed countries.

Figure 4. Contemporary context for building performance objectives.

The most significant change in recent times has been the awareness of the ecological impacts of buildings. Today, society recognizes that the building as a system does not arbitrarily end at the property line, and may have far reaching environmental implications. It is reasonable to expect there will continue to be a variety of interpretations of the relative importance (priority) of the factors involved in the performance of building systems.

Rather than dwell on the global scale of building performance concepts and parameters, this discussion will focus on physical aspects of performance that may be objectively quantified and compared.

Relationship between Physics, Materials, Components, and Systems

Performance concepts in building codes and standards have existed largely as constraints guiding the prescriptive codes and standards development process. One of the major challenges in developing an effective building performance objectives framework has been the establishment of explicit parameters supported by building science knowledge, and specialized knowledge from allied disciplines. These are premised on the relationship between physical phenomena and building system behavior.

A building is a system which consists of materials, components (assemblies, equipment), sub-systems, and systems that interact with physical phenomena in the process of providing an intended level of performance to its immediate occupants and societal stakeholders. Focusing on physical phenomena from a building science perspective, the relationship of the constituent elements of a building system and these physical phenomena is depicted in Figure 5.

Figure 5. Physics, materials, components, and systems.

The key points to appreciate from this relationship are as follows:

• The fundamental physical phenomena imposed on a material, component, or system drive its response (behavior).

• The suitability of a material, component, or system must, as a minimum, adequately address the imposed physical phenomena.

• The complexity of problems increases dramatically as the design process proceeds from selecting materials, to arranging components, to integrating systems.

The relationship can also be used in reverse, figuratively speaking, to assess the suitability of an existing building system to another set of physical conditions which differ from those originally considered in its design.

Due to the multi-functional nature of components and sub-systems (e.g., a wall may provide structural support, fire safety, and moderation of the environment), it is important to relate constituent elements of the building to a coherent hierarchy of objectives. The hierarchy of physics, materials, components, and systems is a practical means of dealing with performance objectives at the conceptual level, recognizing that it may bear little, if any, resemblance to the actual intellectual process (design). The importance of differentiating between representations of relationships, and the actual reasoning processes which make use of these representations, cannot be underestimated. Research in the fields of artificial intelligence and expert systems has demonstrated that the linkages between knowledge representation and its application require sophisticated interpretation.^vi Presumably, the cultivation of sophisticated interpretive skills remains one of the more critical roles for the higher education of design professionals.

A Conceptual Model of Building Behavior

Building behavior (performance) is a highly complex, resultant phenomenon. It involves numerous simultaneous and sequential physical phenomena, and the response of the building as a system will vary depending on the nature and arrangement of the constituent elements. At present, a comprehensive, explicit model of building system behavior has not been developed, but is assumed to exist in some implicit form among the collective of building industry experts. A helpful reminder of the challenge associated with developing a comprehensive system model was provided by Hutcheon (Hutcheon and Handegord, 1983, pp.3-4):

"The design of buildings has been, and still is, to a large extent, based on building practice. Changes have been slow and, in the main, have come about through an evolutionary process of trial and error. Building practice has been fundamentally an inheritance from the past, modified by factors such as climate, economy, social habits, local aesthetic values, and local resources of materials and skills. The evolutionary process works slowly under the influence of new factors; it is equally slow in rejecting the obsolete.

The growth of scientific knowledge has led to great advances in the analysis and rational design of the purely structural functions of a building. There has also been a great deal of development in individual materials and components. As yet, there have been relatively small advances in dealing adequately with all of the combinations of elements and with the complex interrelationships of phenomena involved in the performance of an entire building. The reasons are not hard to find. It is sufficient to note that, even now, contemporary building science draws on the knowledge and experience of almost every branch of engineering science.

We have long since passed the point where we are content to rely on the "trial-by-use" method of assessing changes in design, materials and construction. Many new and interesting materials, systems and methods of design and construction are offered each year. Those responsible for assessing and screening such new developments realize only too well the relative inadequacy of our present knowledge of the suitability of any given material or method. In addition, our standards of performance are continually being raised. As we reduce our major difficulties in turn, minor ones assume greater relative proportions, and we clamour for their reduction or elimination also, in the name of progress. The increasing state of knowledge appears less and less adequate as the demands upon it increase."

Since the time of Hutcheon's observation, a stronger need for a whole system model of building performance has been recognized within the building science discipline. While a broadly accepted model continues to elude building science researchers and practitioners, some advances have been made in various aspects of performance, such as wetting/drying potential of enclosures, window performance, etc. At the conceptual level, approaches such as the general limit states design model have been applied to structural design, however, this approach is not well suited to many areas of building performance (e.g., access and egress, room dimensions, etc.) and the gathering of data may not always be possible even where the model is applicable (e.g., statistics for water leakage in basements).

Given this situation, an attempt to construct a general, extensible schema of building behavior applicable to the whole system, as well as its constituent elements, is presented in Figure 6. At this point, a comprehensive application of the schema to whole building system performance remains to be completed.

Figure 6. Schema describing physical building behavior.

Based on the schema depicted in Figure 6, it may be noted that by linking a number of simple schemata, complex behavior may be described, if not quantitatively modeled. In the example phenomena depicted in Figure 6, the direct response of the building enclosure to the temperature, air pressure, and humidity difference between the indoor and outdoor environments results in heat loss and air leakage. The indirect response influences thermal comfort and indoor air quality if the enclosure provides low effective thermal resistance (excessive thermal bridging and/or insufficient insulation) and the condensation of moisture promotes mold growth. This approach is useful in constructing more sophisticated models of whole system behavior to aid designers with fundamental performance considerations and system interactions.

At this point in the development of contemporary building science, computational methods for the design and assessment of building systems have not emerged. It has been argued that the integrative process of design will remain an exclusively human task, and that conceptual models in the form of computational technologies will only serve as learning aids and practice guidelines. Regardless of the future of building science, a great deal of progress has been made toward developing simple models of building behavior and arranging them within a framework of performance objectives. The next section presents one such approach to the comprehensive assessment of the physical performance of building systems

A Building Performance Objectives Framework

The framework depicted in Figure 7 is an extension of earlier work pursued by the author.^vii It is based on the premise that in the assessment or design process, the key consideration appears to be the performance objective or intent. This view has since been strongly reinforced as many nations move towards objective-based building codes.^viii

An interesting aspect of any objective-based framework is that the intent remains constant while the means of achieving the intent or objective continue to evolve with advances in technology. It appears humans will always expect buildings to provide firmness, commodity, and delight, and that architects will always have to find appropriate means of responding to their clients' demands.

Figure 7. Building performance objectives framework from a building science perspective.

The framework presented in Figure 7 consists of two primary elements:

1. The physical constraints which are imposed by site conditions and the limits or thresholds of the global environment and local ecosystem; and
2. The functional requirements of buildings that encompass occupant requirements, compatibility requirements, and physical requirements.

Contemporary building science supports the societal objective of sustainable architecture by balancing the physical constraints and the functional requirements, ideally without compromising architectural aesthetics and high performance.

The predominant area of interest for building science is under functional requirements, and within this area further and more specific objectives are identified that constitute the basis for designing and/or assessing physical building system performance.

This, or any performance objectives framework, is intended to provide designers with an explicit means of accounting for compliance with the functional requirements of buildings. While it is possible that future developments in computer technology may automate many aspects of design and assessment,^ix it is doubtful that designers will assign significant responsibility to prosthetic applications for assuring due diligence, simply because software cannot shoulder liability.

Finally, if nothing else, this framework exposes the breadth of building science and reinforces the realization that its mastery will require a lengthy commitment to study and practice.

Building System Integration

A common purpose of building science is to achieve building system integration, not by-trial-and-error over many generations of building precedents, but each and every time a building is being designed and built. This implies defining a level of performance and a means of assuring compliance.

Figure 8. Building system integration involves the building structure, its enclosure (envelope), the interior elements, and the building services (i.e., mechanical, electrical, etc.).

Optimizing performance goes beyond compatibility between the structure, enclosure, interior, and services. It involves the assessment of economic, social, and environmental parameters so that performance targets are attained affordably within the skill capacity of the industry. This effectively means innovation may be defined as achieving better performance and higher quality at less cost over the life cycle of a building or facility.

Applied building science research has indicated the control of moisture in building enclosure design generally takes precedence over other control measures simply because so many of the requirements for the control of heat transfer, air leakage and solar radiation are satisfied when all forms of moisture have been carefully considered. At the time of developing this Resource Page, energy efficiency is a primary goal of most developed nations, and this objective is not compromised by designing building enclosures to manage moisture. The levels of thermal insulation needed to avoid interstitial condensation leading to durability problems are equal to, or higher, than those required to provide cost effective levels of energy efficiency over the life cycle of a building. This is the rationale behind a subsequent set of building science Resource Pages beginning with moisture management in building enclosures.

A number of related Resource Pages are also dedicated to explaining how various performance objectives identified herein may be achieved, but for the purposes of understanding building science concepts, it is important to appreciate that the building enclosure, or envelope, is the primary environmental separator/moderator. It performs a passive role, unlike mechanical and electrical systems, that actively supplement the amount of heat, air, moisture, and daylight the enclosure is unable to provide. When all active systems fail, the building enclosure is the last line of defense between the indoors and the outdoors. High-performance building enclosures provide passive sustainability during extreme weather phenomena and natural disasters, and safely shelter their inhabitants.

Synopsis

In summary of the ideas and relationships that have been presented, the following conclusions may be considered:

• Buildings are systems that must be appropriately integrated by designers to achieve defined levels of performance.

• Building science provides a disciplined means of dealing with the physical requirements of buildings that is completely compatible with the architectural design and building construction processes.

• Innovation in modern architecture relies on building science and the systems approach to ensure that building performance meets the expectations of building owners, inhabitants, and society.

• The context for building performance has more recently evolved to include issues of ecology and sustainable development. This expansion of performance parameters, coupled with increasing consumer expectations, has dramatically increased the complexity of buildings. Performance objectives frameworks and conceptual models have become necessary methodologies to assure all aspects of the integration of well performing building systems have been carefully addressed.

For further study on this topic read the concluding chapter to Robert Mark's compendium on Architectural Technology Up to the Scientific Revolution wherein he observes:

"By focusing on a wide range of historic buildings, from their below-ground-level foundations to the peak of their timber roofs, the typical developmental pattern of pre-scientific technology becomes evident. Much of what was then learned through experience and observation is available to today's designers from scientific analysis."^x

Contemporary building science has evolved beyond simple analysis and now offers a range of sophisticated design tools, testing protocols, and performance simulation/validation techniques. These have become invaluable supplements to professional experience and the critical observation of actual building performance. The role of contemporary building science within architecture and engineering continues to reinforce the dynamic relationship between theory and practice in the AEC industry.

Additional Resources

Publications

• Building Science for a Cold Climate by Neil Hutcheon and Gus Handegord. Institute for Research in Construction, 1983.
• The Building Systems Integration Handbook, edited by Richard D. Rush. The American Institute of Architects, 1986.
• Building Science for Building Enclosures by John Straube and Eric Burnett. Building Science Press, December 2005.
• Integrated Buildings: The Systems Basis of Architecture by Leonard R. Bachman. John Wiley and Sons, 2003.

Online Sources of Building Science Information

Building science information can be found among a number of sources, such as conference proceedings, journals, studies, and various technical publications made available through government, industry and academia. The sources cited herein represent organizations or institutions that are predominantly involved with building science. For example, sources such as the American Society of Civil Engineers will have a part of their publications dedicated to building science, but for the most part, focus on traditional civil engineering topics. These kinds of organizations have not been listed, but may contain highly relevant building science information.

• Building Science Centre of Excellence Research Database
• Building Science Corporation
• Canada Mortgage and Housing Corporation—Accessible and Adaptable Homes
• Lawrence Berkeley Laboratory—Building Energy Efficiency
• National Institute of Building Sciences
• National Institute of Standards and Technology—Buildings and Construction
• National Renewable Energy Laboratory—Buildings Research
• Natural Resources Canada—Energy Efficiency for Buildings
• Oak Ridge National Laboratory—Building Technologies Program

In addition to the sources cited above, keyword searches on the Internet will yield a number of references for a particular topic. Product manufacturer organizations and government departments dedicated to buildings, or aspects of buildings such as energy efficiency, are also potential sources of invaluable building science information. In order to obtain maximum benefit from these myriad sources of building science information, it is important to gain a foundation of fundamental building science concepts and terminology.

References

i. Building Science for a Cold Climate, NRCC 39017 by Hutcheon, N. B. and Gus Handegord. Ottawa: 1983.

ii. Fields of Research in Building Science (brochure) by Education Liaison Committee. Washington, DC: Building Research Institute, 1963.

iii. 3 Definitions as found in: Hierarchy theory: a vision, vocabulary, and epistemology by Timothy F. H. Allen with Valerie Ahl, illustrated by Paula Lerner. New York: Columbia University Press, 1996.

iv. Fundamental Considerations in the Design of Exterior Walls for Buildings, Technical Report No. 13, Division of Building Research by Hutcheon, N. B. Ottawa: National Research Council Canada, 1953.

v. Development of a Wall Performance Classification System by Kesik, T. and David De Rose. Toronto ON: CIB World Building Congress 2004, May 2–7, 2004.

vi. Knowledge in the Form of Patterns and Neural Network Computing Knowledge Engineering, Volume I, Fundamentals by Pao, Y.H., H. Adeli (editor). New York: McGraw Hill, 1990.

vii. A Knowledge Based Systems Approach to the Assessment of Building Performance Proceedings of the Second Canadian Conference on Computing in Civil Engineering, pp. 469-480 by Kesik, T. and K.A. Selby. Ottawa, Ontario: 1992.

viii. Objective Based Codes: A New Approach for Canada by Canadian Commission on Building and Fire Codes. Ottawa: February 1996.

ix. Towards Integration of Service Life and Asset Management Tools for Building Envelope Systems Proceedings of the Seventh Conference on Building Science and Technology, pp. 153-163 by Lacasse, M.A., D.J. Vanier, B.R. Kyle. Toronto: 1997.

x. Architectural Technology Up to the Scientific Revolution by Mark, Robert (editor). Cambridge, Massachusetts: MIT Press, 1993.

Introduction

Little has more impact on our lives than the built environment around us. That built environment exists because of the professionals and skilled tradespeople from multiple disciplines that plan, design, construct, operate, and manage it. They focus on meeting important needs of citizens including providing sustainable, cost effective and safe environments for living, working, playing and learning.

Today's buildings-related professionals and tradespeople make use of cutting edge technology including building information modeling (BIM), computerized maintenance management systems (CMMS), smart controls and renewable energy systems such as solar photovoltaics and wind to deliver high-performance buildings.

For those students interested in pursuing building operations related careers, the Department of Energy, General Services Administration, National Institute of Building Sciences, the Consortium for Building Energy Innovation, Penn State University and Facility Engineering Associates have developed a career map for Building Operations Professional, Energy Auditor, Building Commissioning Professional, and Energy Managers. The Facilities Career Map demonstrates what possible careers look like in terms of sequential positions, roles, credentials, experience and education/training.

The information contained here is intended to provide an introduction to the various disciplines and opportunities within the buildings industry. You are encouraged to explore the rest of the Whole Building Design Guide and contact the organizations identified below for additional insight into career opportunities.

This career center supports the Mars City Facility Ops Challenge developed by the National Institute of Building Sciences, Total Learning Research Institute and National Aeronautics and Space Administration but provides tools for anyone considering a career in the buildings-related disciplines.

Building Science Disciplines

Architecture

• John Jackson, Architect, HOK  
• American Institute of Architects (AIA) Career Stages

Architectural Programming

Building Scientist

• Paul Totten, Building Scientist, WSP Group  
• Building Science Concepts

Code Official

• Peter Mensinger, Code Official, City of Alexandria, VA  
• International Code Council (ICC) High School Technical Training Program

Commissioning Authority

Cost Estimating

Electrical Engineering

Fire Protection Engineering

• Careers in Fire Protection Engineering, SFPE

HVAC and Refrigerating Engineering

• Dunstan Macauley, Mechanical Engineer, WSP Group  
• ASHRAE K-12 Activities
• HVACR Workforce Development Foundation: Careers In HVAC
• Why Become an HVAC Technician
• Why Choose a Career in HVACR

Information Technologies Engineering

Interior Design

• Deborah Davis, Interior Designer, Deborah Davis Design  
• American Society of Interior Designers (ASID) Student Resources

Landscape Architecture

• Radhika Mohan, Landscape Architect and Urban Planner, City of Alexandria, VA  
• American Society of Landscape Architects, Become a Landscape Architect
• Landscape Architecture and the Site Security Design Process

Lighting Design

• David Ghatan, Lighting Designer, CM Kling + Associates  

Planning

Plumbing Engineering

Researcher

• Lisa Choe, Building Science Researcher, National Institute of Standards and Technology (NIST)  
• Harrison Skye, Building Science Researcher, National Institute of Standards and Technology (NIST)  
• Guide to NIST's STEM Education Activities

Structural Engineering

• Robert Victor, Structural Engineer, HDR  
• American Society of Civil Engineers (ASCE) Pre-College Outreach

Sustainability Specialist

• Fulya Kocak, Sustainability Director, Clark Construction  
• U.S. Green Building Council (USGBC) Center for Green Schools

Welding / Welding Engineering

• Careers in Welding

Woodworker

• Tony Daggett, Cabinet Maker, Architect of the Capitol  

Major Resources

Industry STEM/STEAM Education Initiatives

• International Code Council (ICC) High School Technical Training Program

References

• Industry Organizations

Introduction

Much progress has been made on improving building energy efficiency over the past decades by focusing on the efficiency of individual building components (i.e., appliances and equipment) and, more recently, the efficiency of the building as a whole. As a middle ground between component and whole-building efficiency, a building systems approach considers the interactions of components within and among building systems, as well as interactions among multiple buildings, and between the building and the electric grid. Adopting a systems perspective will become increasingly necessary to achieve meaningful and cost-effective future energy savings within the built environment.

In addition to improving energy performance, a systems approach has the potential to achieve significant non-energy benefits: reduced carbon emissions (commercial buildings alone account for about 18 percent of direct and indirect greenhouse gas emissions), improved grid reliability , water savings , and extended equipment life and increased occupant comfort and productivity . The quantifiable non-energy benefits have been estimated to range from 25 to 50 percent of the total benefits of energy efficiency across all sectors.

Description

Defining Systems Efficiency and its Role in Whole Building Design and Operation

A building system is a combination of equipment, operations, controls, accessories, and means of interconnection that use energy to perform a specific function. Examples include HVAC, water heating, lighting, thermal envelope, and miscellaneous electrical load systems.

• System energy efficiency is defined as the ratio of the services or functions provided by a building system to the amount of energy that system consumes, taking into account the thermal load imposed on (or thermal energy contributed to) other building systems.
• " To achieve a systems-efficient building, multiple systems (e.g., lighting, HVAC&R) must be designed, installed, and operated to optimize performance collectively with other energy systems both within and outside of the building to provide a high level of service for a given level of energy use.

Whole Building Design includes both an integrated design approach and an integrated team process. An integrated design approach ensures that the interrelationships and interdependencies with all building systems are understood, evaluated, appropriately applied, and coordinated concurrently from the planning and programming phase. Systems efficiency is one of the strategies used to implement Whole Building Design.

The Case for a Systems Approach

Improving the efficiency of building systems will support the WBDG objectives for sustainable, cost-effective, functional, and secure/safe, whole-building design and operation.

Energy Savings

Despite decades of improvement in equipment efficiency, the overall energy use of U.S. commercial buildings continues to increase. Energy intensity (energy/floor area) has been declining but not fast enough to offset floor space growth - due in part to the rapid increase in miscellaneous loads, which also create additional cooling loads. By 2035, miscellaneous end-uses are projected to use as much energy as all other building end-uses combined. The combination of these new loads and growing floor space means that new approaches to efficiency will be needed to stem overall growth in building energy use. Optimizing performance at the systems and multi-systems level offers one promising path forward.

Examples of energy savings potential include:

• A DOE study in 2011 identified a number of systems-level technologies, including solar-enhanced (desiccant) cooling, demand-controlled ventilation, and a dedicated outdoor air system to separately control latent and sensible cooling, individually had the potential to save between 0.1 and about 1.1 Quads/year of energy if applied to commercial buildings nationwide.

• A 2012 meta-analysis of the literature on energy savings from lighting controls in commercial buildings looked at 240 studies, concluding that national savings from various strategies would be ". . . 24 percent for occupancy [controls], 28 percent for daylighting, 31 percent for personal tuning, 36 percent for institutional tuning, and 38 percent for combined approaches".

• A 2013 study of a high-performance office building in New York City measured the impact of lighting controls (along with other measures) on three floors. Energy savings of 56 percent resulted from daylight dimming controls and setpoint tuning in the daylighted spaces, compared to a code-compliant (ASHRAE 90.1-2001) building with scheduled on/off controls only.

Cost—Effective

Some mechanical equipment, light sources, and other building components are approaching technical and economic limitations for achieving further efficiency improvements. As these limits are approached, the costs of marginal efficiency improvements at the component level will rise. A systems approach offers creative avenues to further, cost-effective energy savings.

Support for Appropriate Product/Systems Integration

(For Functional/Operational Objective)

Highly efficient components do not necessarily result in an efficient building. Optimized building efficiency requires consideration of the interactions among components and with the building.

Secure and Safe

Emerging opportunities for attaining significant efficiency gains-such as through the integration of smart grid connectivity and related control technologies-are optimally applied at the system level. Buildings-to-grid integration can enhance grid reliability. Conversely, when a grid outage does occur, systems such as passive solar design, natural ventilation, daylighting, thermal storage, and on-site generation coupled with battery storage allow a building to remain functional and habitable for an extended period.

Microgrids can enhance systems efficiency by allowing for dynamic interactions among distributed energy resources, the utility grid, and loads. Credit: Nordman, B., Khandekar, A., Spears, M., & Pezzola, M. (2017). Lawrence Berkeley National Laboratory. A Simulation of Local Power Distribution Control Strategies, presented at Second International Conference on DC Microgrids, Nurnburg, Germany, 2017.

System Efficiency Applications

Several building systems can reduce energy consumption through improved controls , thermal exchanges, and multi-systems integration. While these measures may be easier to apply to new construction and major renovations, the majority of savings potential lies in changes to existing buildings. Opportunities for systems solutions in existing buildings are often associated with control systems installation or upgrades, interior renovations to accommodate new tenants, and end-of-life replacement of HVAC and other mechanical systems. Following are some examples of system efficiency measures:Lighting and Daylighting Systems

Energy used for lighting represents about 10 percent of commercial building electricity use. As defined by NEMA, an optimal lighting system is "a collection of luminaires and related lighting equipment installed in an application to provide the right amount of light where and when needed, with consideration of human comfort, visibility, safety and security, the physical environment, and daylight integration." Although energy efficient lighting components are critical, effective lighting and daylighting system design and controls can add significant energy savings. A lighting controls study in two GSA federal office buildings with updated LED lighting resulted in measured savings of 32-33 percent of lighting energy.

HVAC&R Systems

Energy used for HVAC&R systems represents over 50 percent of commercial building electricity use. HVAC&R systems (space cooling, space heating, ventilation, and refrigeration) are by far the largest users of energy in commercial buildings. In order to Optimize Energy Use, designers must consider specifying efficient HVAC systems, including efficient water— or air—based distribution, variable—speed controls, demand—based ventilation and heat or enthalpy recovery. Many potential sources of low-level heat, such as heat rejected from HVAC or refrigeration systems or from telecom and server rooms, could be captured for beneficial use in pre-heating hot water systems or to condition outside ventilation air.

Hot Water Systems

Building designers should prioritize the design of hot water distribution systems (e.g., pipe layout and the location of the heating system relative to points of use) to minimize the total heat lost while serving the load.

Motor Systems

Shifting to a systems approach that considers additional factors such as drivetrains, inverters and electronic drive controls—as well as the choice of motor—driven system components (e.g., for pumps and air—handlers)–has the potential to substantially increase the efficiency of the total motor system.

Miscellaneous Electric Loads

Miscellaneous electric loads (MELs) together currently account for about 28 percent of primary energy in commercial buildings, and in some high-efficiency buildings, over 50 percent of the electric load. According to DOE,

"…the amount of energy savings from replacing an individual device often does not justify the replacement cost. As a result, there is a need for developing overarching technological solutions that can achieve crosscutting reductions in energy consumption at minimum cost. Instead of targeting individual MELs, R&D advancements require going up one level (to systems of MELs) or down one level (to common MELs components)".

Strategies to reduce MELs include:

• Energy reduction at the device level by improving device efficiency
• Enhanced control of an individual device to reduce standby power
• Integration of MEL device controls with system-level sensors and controls and with other building systems to optimize building operation

Multi-systems Integration

To maximize whole-building efficiency we must recognize that buildings are made up of multiple systems and optimize their integrated performance. Integrated systems provide the controls and feedback needed for buildings to operate at peak efficiency.

Direct Current (DC) Power

As a multi-systems strategy, direct current power distribution within a building can reduce energy demand as well as contribute to grid balancing, expanded control options, and improved safety and reliability. DC distribution can deliver systems-oriented energy savings for lighting, MELs, and many HVAC&R components by:

• Reducing alternating current-to-DC (AC/DC) conversion losses and AC/AC transformer losses, in both active and "standby" modes.
• Making it more feasible to replace AC-driven devices with "native-DC" devices for computers, telecommunications, and consumer electronics, as well as for lighting, control systems, and motors (especially those in variable-load applications).
• Enhancing the value of native-DC on-site photovoltaic generation and battery storage by avoiding conversion losses.

Emerging opportunities for attaining significant efficiency gains-such as through the integration of smart grid connectivity and related control technologies-are optimally applied at the system level.

A Building Integrated Photovoltaics (BIPV) System is one example of an opportunity for DC distribution. Implementation of a BIPV system in combination with energy storage has the potential to reduce a building's billed energy charges by 42% – and DC distribution can provide further savings by avoiding multiple DC/AC/DC conversions.

Multi-building Systems: CHP and DES

Better integration of energy systems applies both within and outside the building boundary. Examples include Combined Heat and Power (CHP), District Energy Systems, and Buildings-to-Grid Integration.

Combined Heat and Power (CHP)

CHP systems have the potential not only to save energy and reduce building operating costs but also to enhance building operational resilience and grid reliability ("Valuing Resiliency: How Should We Measure Risk Reduction?"). In addition to the potential direct energy savings from CHP (such as doubling the useful energy products derived from fuel used, there are three categories of CHP "resilience value":

1. Continued operation during major (low-probability/high-consequence) events;
2. Power reliability under routine conditions; and
3. Improved power quality

Combined Heat and Power (CHP) systems have the potential not only to save energy and reduce building operating costs but also to enhance building operational resilience and grid reliability. Credit: US EPA, Combined Heat and Power Partnership.

District Energy Systems (DES)

District energy systems can often improve energy productivity and energy diversity while reducing GHG emissions. According to the UN Environment Program, DES can reduce heating and cooling energy in urban buildings by as much as 30-50 percent . District energy is intrinsically open to diverse fuel sources on the thermal side; when combined with CHP it can diversify the source of both electricity and heat. DES systems can also be readily incorporate ice storage tanks to offset peak demands or to make better use of surplus generation from intermittent wind and solar resources. For the estimated 290 district energy systems in the U.S. that do not currently use CHP, conversion to CHP represents a tremendous opportunity for efficiency improvement .

Related/Emerging Issues

Developing System Metrics

Current metrics and regulations typically address rated equipment efficiency or whole-building performance as designed, but most do not address actual performance of equipment or buildings as installed and operated - although recent initiatives on outcome-based performance pathways represent a promising new direction.

New systems-level metrics, standards and tools could support the improved performance of building systems through system design and commissioning, in ways that consider typical building load profiles, operating patterns and regional climate conditions.

Systems Strategies for Existing Buildings

With about 5.6 million commercial buildings as of 2012 with expected lifetimes of several decades, it is clearly important to develop system-oriented retrofit strategies for the existing building stock as well as new construction. In existing buildings, integrated system retrofits can be implemented through a variety of approaches. These include:

• Retro-commissioning
• Controls retrofits to existing systems
• Building renovation
• Deep retrofits or sequenced planned retrofits

Systems Solutions for Smaller Buildings

As with the existing building stock, smaller commercial and residential buildings pose a special challenge to systems efficiency. Efficient systems solutions often require detailed energy modeling and design analyses, which are seldom cost-effective for smaller buildings. Thus, new approaches such as "packaged" system solutions need to be developed.

Reliability and Resiliency

As discussed above, efficiency gains in systems within the building (HVAC &R, lighting, MELs, etc.) and those outside the building such as CHP and DES all represent opportunities to reduce stress on the utility grid during peak demand periods and in case of unforeseen generation, transmission, or distribution outages, thereby enhancing the grid's reliability and resiliency. Emerging opportunities for Building-to-Grid (B2G) Integration offer the prospect of improved operational savings and reliability on both sides of the meter.

The evolution of a fully integrated, transaction-based building-grid and ecosystem will create new opportunities for optimizing system efficiencies, reliability and cost-effectiveness at both the building and grid scale, while paving the way for more effective integration of renewable resources and electric vehicles.

DOE's Grid Modernization Laboratory Consortium (GMLC) is working towards creating a next-generation grid operating system using grid-level integration of Energy Management Systems (EMS), Distribution Management Systems (DMS), and Building Management Systems (BMS), resulting in operations with less reserve margin and dramatically enhancing the energy and economic efficiency of the system. Systems integration and improved control systems (for example, GMLC's "Multi-scale Integration of Control Systems" also can lead to building improvements that have many other associated energy and non-energy benefits, including improved comfort, lower cost, and better integration of microgrids and distributed energy resources (e.g., solar PV, wind energy).

Relevant Codes, Standards, and Guidelines

• ANSI/ASHRAE/IES/USGBC Standard 189.1-2014, Standard for the Design of High-Performance Green Buildings
• ANSI C137.1, Lighting Systems
• Energy Star, certification for your building
• LEED Building Certifications
• LEED BD+C: Core and Shell Development — Green Building Council. This certification program provides incentives for systems efficiency as follows:
• Alternative Energy Performance Metric
• Optimize energy performance
• Integrative process
• Alternative performance rating method
• District energy

Additional Resources

Tools, Policies, and Ongoing Research that Support, Systems Efficiency

• Army Net Zero Initiative – U.S. Department of Defense. This initiative is a strategy for managing existing energy, water, and solid waste programs with the goal of exceeding minimum targets, where fiscally responsible, to provide greater energy and water security and increase operating flexibility.
• Energy Performance of Buildings Directive – EU of the European Parliament and of the Council. European legislation covering the reduction of the energy consumption of buildings.
• Implementing an Outcome-Based Compliance Path in Energy Codes: Guidance for Cities – National Institute of Building Sciences and New Building Institute. This report can be found on the Whole Building Design Guide's webpage titled Outcome-based Pathways for Achieving Energy Performance Goals.
• MotorMaster+ – U.S. Department of Energy. MotorMaster+ enables industrial energy coordinators, facility managers, and plant electricians to manage their motor inventory and maintenance logs in order to evaluate their energy efficiency and discover new ways to reduce energy use, thereby cutting costs and eliminating environmental impact.
• Performance Excellence in Electricity Renewal (PEER) – Green Business Certification Inc. This rating system for utility system energy efficiency and environment includes an incentive for Systems Energy Efficiency.
• S. 1874, Distributed Energy Demonstration Act of 2017 – Bill introduced by Senator Wyden.
• S. 1875, Flexible Grid Infrastructure Act of 2017 – Bill introduced by Senator Wyden.
• S. 1876, Reducing the Cost of Energy Storage Act of 2017. – Bill introduced by Senator Wyden.
• Savings by Design – California Utilities and Public Utilities Commission. This program offers incentives for building owners and design teams to take a systems efficiency approach.
• Smart Readiness Indicator for Buildings – VITO NV. This study provides technical support to the Directorate-General for Energy of the European Commission regarding potentially setting up a 'Smart Readiness Indicator (SRI) for Buildings'. SRI would give recognition for smarter building technologies and functionalities which enhance the energy efficiency and other pertinent performance characteristics of the building stock.
• Systems Program Manuals and Assessment Methods – Lawrence Berkeley National Laboratory. These program manuals allow the user to go "beyond widgets" by taking a systems level approach to realize deeper energy savings.
• VOLTTRON Controller for Integrated Energy Systems to Enable Economic Dispatch Improve Energy Efficiency and Grid Reliability – Grid Modernization Laboratory Consortium. This project will design, develop, field test, and commercialize a multi-purpose controller and associated open-source algorithms that will ensure real-time optimal operation, increase electric grid reliability, and lead to the goal of clean, efficient, reliable and affordable next generation integrated energy system (IES).

References

• 2012 Commercial Buildings Energy Consumption Survey: Energy Usage Summary, Table 5., U.S. Energy Information Administration (EIA), 2012
• Annual Energy Outlook, U.S. Department of Energy (U.S. DOE), 2015
• ANSI C137 Lighting Systems Committee, National Electrical Manufacturer Association (NEMA)
• Building Energy Codes Program: National Benefits Assessment, 1992-2040, by Livingston, O.V., P.C. Cole, D.B. Elliot, and R. Bartlett. Rep. no. PNNL-22610 Rev 1. Prepared for the U.S. Department of Energy. Oak Ridge, TN: Pacific Northwest National Laboratory, 2014
• Buildings Energy Efficiency Frontiers & Innovation Technologies (BENEFIT)-2017 Funding Opportunity Announcement (FOA) Number: DE-FOA-0001632, by the U.S. Department of Energy (U.S. DOE) 2016
• District Energy in Cities-Unlocking the Potential of Energy Efficiency and Renewable Energy, by the UN Environment Program (UNEP), ND
• Enhancing Community Resilience through Energy Efficiency, by Ribeiro, D., Mackres, E., Baatz, B., Cluett, R., Jarrett, M., Kelly, M., and Vaidyanathan, S.. ACEEE, October 2015
• Energy Savings Potential and Research, Development, and Demonstration Opportunities for Commercial Building Heating, Ventilation, and Air Conditioning Systems: Final Report. Navigant report for DOE, by Goetzler, W., R. Zogg, H. Hiraiwa, J. Burgos, and J. Young. 2011
• Green Buildings Matter, by Moore, Michelle. The American Prospect, 17 December 2006.
• Impacts of Commercial Building Controls on Energy Savings and Peak Load Reduction, by Pacific Northwest National Laboratory, May 2017
• Loads Providing Ancillary Services: Review of International Experience, by Heffner, G., C. Goldman, B. Kirby, and M. Kintner-Meyer. May 2007
• Miscellaneous Energy Loads in Buildings ACEEE Rep. no. A133, by Kwatra, S., J. Amann, and H. Sachs. [http://aceee.org/research-report/a133] 27 June 2013
• Reducing Plug and Process Loads for a Large Scale, Low Energy Office Building: NREL's Research Support Facility, By "Lobato, C., S. Pless, M. Sheppy, and P. Torcellini. 2011 (b). NREL/CP-5500-49002. Oak Ridge, TN.
• A Post-Occupancy Monitored Evaluation of the Dimmable Lighting, Automated Shading, and Underfloor Air Distribution System in The New York Times Building, by Lee, E.S., L.L. Fernandes, B. Coffey, A. McNeil, R. Clear, T. Webster, F. Bauman, D. Dickerhoff, D. Heinzerling, and T. Hoyt. LBNL-6023E. January 2013
• Quantifying National Energy Savings Potential of Lighting Controls in Commercial Buildings, by Williams, A., B. Atkinson, K. Garbesi, and F. Rubinstein. ACEEE, 2012
• Recognizing the Value of Energy Efficiency's Multiple Benefits. Research Report IE1502, by Russell, C., B. Baatz, R. Cluett, and J. Amann. American Council for an Energy-Efficient Economy, 2015
• Saving Water in Office Buildings, by the U.S. Environmental Protection Agency (EPA), January 2017
• Smart Tools in a 111d Toolbox: Combined Heat and Power and District Energy, by the International District Energy Association (IDEA). N.D.
• Solar + Storage Synergies for Managing Commercial-Customer Demand Charges, Slide #13, by Gagnon, P. et al. 2017
• The U.S. Appliance Standards Program (a), by the U.S. Department of Energy (U.S. DOE), April 2015
• Valuation of Transactive System, by Pacific Northwest National Laboratory, May 2016
• Valuing Resiliency: How Should We Measure Risk Reduction? Proceedings of the 2016 ACEEE Summer Study on Energy Efficiency in Buildings, by Chittum, A. Asilomar, CA: August 2016
• Windows and Offices: A study of worker performance and the indoor environment, Prepared by Heschong Mahone Group Inc. California Energy Commission, 2003
• Wireless Advanced Lighting Controls Retrofit Demonstration, by Wei, J., F. Rubinstein, J. Shackelford, and A. Robinson. Lawrence Berkeley National Laboratory. Rep. no. LBNL-183791, April 2015

Department of Energy (DOE) - Industrial Technologies "Save Energy Now" (SEN) Program

Energy is often one of the most costly components of operating any manufacturing facility and its processes. A reduction in energy consumption reduces cost. Without exception, this is a continual objective of most companies. It may not be at the top of the list, but certainly within the top ten of corporate initiatives. While insulation can be one of the easiest, fastest and least costly "technologies" to reduce energy cost, it is often the last option considered.

It is interesting to review the process for determining the design criteria for insulation on new construction or expansion projects verses the maintenance process and how priorities are established. In new construction, the primary driver in determining the insulation system is the process. Very seldom is the insulation system or thicknesses examined from an energy conservation perspective. Once a facility or plant is operating and the energy consumed is a reality, as opposed to a theory, it seems that compliancy or acceptance of the results outweighs examining actual results in comparison to original expectations. Properly and timely maintaining an insulation system seems to mostly reactionary verses proactive.

It has been estimated that between 10—30% of all installed mechanical insulation is either damaged or missing. The question that must be asked is why does this condition exist when it can be corrected and provide a significant return on the capital employed or maintenance dollars expended?

The Department of Energy (DOE) - Industrial Technologies, "Save Energy Now" (SEN) Program is part of a national campaign by the DOE to help manufacturing facilities reduce energy and operating costs and operate more efficiently and profitably. Independent specialists who have been trained in the utilization of sophisticated software assessment tools and have passed a rigorous qualifying exam, visit a plant and work with personnel to identify immediate and long-term opportunities for improving energy efficiency and bottom-line results. Mechanical insulation is one of the many opportunities that are examined.

Of the SEN assessment studies published to date (September 07), 53% have identified replacing, repairing and upgrading the mechanical insulation as an opportunity of which 84% have estimated a return on investment in less than a year.

Following are but a few example excerpts from the SEN survey results which are classified as "near term" opportunities—payback in less than one year: (Assessment results determined by review and interpretation of available data. (Please refer to the Save Energy Now web site, www.eere.energy.gov/industry/saveenergynow, for specific and detailed information on these and other examples. The information shown does not depict all aspects of the reported assessment results for the respective facility)

Bayer (2 Steam Plants), Institute, WV
By improving and replacing missing insulation on the steam and condensate lines - Potential savings $926,000 per year

Boise Cascade (Paper Mill), Jackson, AL
By replacing missing pipe insulation - Estimated savings $80,000 per year, cost to complete the work $25,000 = 3.8 month payback

Dow Chemical (Chemical Plant), Hahnville, LA
By replacing, repairing and improving insulation on steam system - Potential annual savings of $811,000

General Motors (Power Plant), Pontiac, MI
By replacing missing insulation and repairing other areas - Estimated annual savings of $298,000

Goodyear, Union City, TN
A significant number of process units are partially insulated. Potential savings, $402,000 per year. Estimated payback 2.5 to 6 months depending upon cost of completing the work. "This same opportunity can be applied to other company facilities."

National Starch (Power Plant), Indianapolis, IN
By replacing and repairing insulation - Estimated annual savings of $125,000

Sterling Chemical (Chemical Plant), Texas City, TX
Improvements in the insulation - Potential annual savings of $123,000

Mead Westvaco, Silsbee, TX
Commissioned an "Insulation Strike Team" to go through the plant to repair areas of poor, damaged or missing insulation. They determined that reducing insulation heat loss by 10% would yield savings of over $486,000 per year

United States Steel, Gary, IN
Estimated that by using proper type, size and thickness of insulation and improving maintenance of the insulation systems could result in annual savings in excess of $1,500,000 per year

Mittal Steel, Weirton, WV
By insulating hot water washing tanks, 140 F operating temperature, located throughout the facility, 50,000 SF of surface area, with an inexpensive - simple insulation system the annual savings would be $371,000 + per year

Eastman Chemical, Kingport, TN
"The thermal insulation system throughout the site is observed to be in good condition...several pipes observed to be missing insulation. The approach taken in investigating and illuminating insulation issues is excellent and considered to be a Best Practice approach"
One heat tracing system is not completely evaluated yet - identified savings $1,000,000 with re-insulation cost of $300,000 = 4 month ROI
Steam system will be evaluated - preliminary investigation indicate a potential savings of additional $1,000,000 with return ranging from 1 to 3 years

"Improving From the Outside In" Insulation upgrades to the outside pipelines at NOCO Energy Corporation improve energy efficiency-and the company's bottom line.

NOCO Energy Corporation has a large terminal operation outside of Buffalo, New York, in Tonawanda. From that terminal, NOCO distributes petroleum and petroleum products to the western New York area. Among the petroleum-based products that NOCO distributes are asphalt and No. 6 fuel oil, which must be kept in heated storage tanks and distribution pipelines. Without heated tanks, piping, and equipment, these products cannot be pumped.

Multiple Challenges To Meet

Over the years, it became increasingly difficult for NOCO to maintain adequate temperatures in storage tanks and pipelines. This resulted in slow pumping and transfer rates through the pipelines, as well as periodic plugging. These problems made it difficult to run the terminal efficiently and cost-effectively.

NOCO's location along the shore of Lake Erie in western New York did not help. Winter temperatures can reach -20°F, annual snowfall surpasses 90 inches, and winds average 12 miles per hour (mph), with peak winds well over 50 mph. These severe factors made maintaining sufficiently high operating temperatures more difficult—and even more critical.

The situation was aggravated further by the terminal layout. It is spread out, requiring long pipelines from the lakefront barge-loading facilities and the storage tanks. Additionally, the terminal used a heated-oil heat transfer fluid to maintain the temperatures in the storage tanks and pipelines, with the heaters located at the northern end of the terminal. This also made for long heated-oil transfer lines.

The final problem was the terminal's damaged insulation systems, especially on the product pipelines and heated-oil supply lines. All of these lines are located in ground-level horizontal pipe racks. Over the years, between people stepping on the pipelines, maintenance activity, and the effect of the Buffalo-area weather, the insulation systems degraded. The systems' poor condition contributed significantly to the terminal's difficulty maintaining temperature in the asphalt and No. 6 fuel oil tanks and pipelines.

First Solutions First

Revision of the heated-oil transfer system was the first priority. Management submitted a project to design and install another heated-oil heater, located toward the southern section of the terminal. Revising the system would improve heat transfer and pumping efficiency.

The terminal staff believed upgrading the insulation systems would improve the overall reliability and efficiency of the systems, as well as save on energy costs. With the help of the New York State Energy Development and Research Authority (NYSERDA)—see "NYSERDA Offers Energy-Saving Expertise"—and the engineering firm Clough, Harbour, & Associates, they performed an evaluation of all of the insulation systems and determined the economic impact of upgrading all affected insulation systems, including the addition of 2 inches of insulation to the existing 2 inches. Because the terminal had a readily available, low-cost fuel source for the heated-oil heaters in used motor oil, the initial evaluation indicated an unusually long payback period for an insulation upgrade project like this—around 3 years.

An Unexpected (and Lucrative) Turn of Events

About the time the original assessment was performed, terminal staff found that the used motor oil being used for fuel in the heated-oil heaters was in greater demand. So any fuel saved from burning in the heated-oil heaters could be sold profitably. This increased interest in the insulation upgrade.

The new heated-oil heater was installed, but only some of the insulation was upgraded for several reasons, including schedule, equipment availability, and budget. Part of the problem was the fact that the insulation systems were much more damaged than originally assumed and had to be completely replaced.

Because the addition of the new heated-oil heater and some rerouting of heated-oil lines were projected to actually increase fuel consumption and cost to the terminal, it became more complex to analyze the benefit of the insulation upgrade project to the overall facility.

Through the efforts and resources of NYSERDA, a review of the work and an analysis of the energy savings on the upgraded insulation systems were performed using both proprietary and 3E Plus® software (see "The Power of 3E Plus"). The following are the results of the analysis:

• Projected energy savings of approximately 10 billion Btus per year or more than $87,000
• Projected used motor-oil savings (that can be sold in the marketplace at approximately $1 per gallon) of around 87,000 gallons
• Projected payback: slightly more than 1 year
• Carbon dioxide (CO2) reduction: more than 2.3 million pounds of this greenhouse gas per year
• More than 4,500 pounds of nitrogen-oxygen compounds (NOx) class of regulated emissions, which includes both greenhouse gases and other gases that influence the mixing ratio of greenhouse gases

"Though it is difficult to quantify the fuel savings that resulted from this project, the original heating system was grossly undersized for our needs," says Val Speek, terminals and facilities manager at NOCO Energy Corporation. "Burners were running at a 100-percent firing rate and were unable to meet the Btu demand for heating our asphalt. The addition of a new thermal fluid heater and the replacement of damaged insulation resulted in a surge of customer satisfaction. The heater played a major role in maintaining our marketing tanks at an acceptable temperature, while the replacement of damaged line insulation increased efficiency and eliminated customer complaints of cold asphalt".

"This is the first year I can remember having no problems loading asphalt in the cooler weather," Speek adds.

Paul D. Tonko, NYSERDA's president and chief executive officer (CEO), says, "Through NYSERDA's FlexTech program, we've assisted NOCO in operating its distribution terminal more efficiently while maintaining profitability. Our study of the facility identified significant areas of energy-efficient infrastructure and productivity improvements to the rail facility, heat transfer system, tank farm, and pump motors. As a result, NOCO's $5-million capital investment has led to $500,000 per year in energy and productivity benefits, 16 indirect jobs, and the equivalent of 20,000 barrels of oil saved annually. NYSERDA is proud to have partnered with NOCO Energy Corporation and Clough, Harbour, & Associates in making the necessary energy efficiency upgrades at the facility."

Even better than the projected cost savings and emission reductions from energy efficiency is the fact that the properly insulated lines now pump product easier and faster, with far fewer plugging problems, allowing the terminal to operate more efficiently and profitably. The facility's overall result is a win-win situation—a better-running terminal, more recycled motor oil to sell rather than burn in the heated-oil heaters, and less environmental impact due to fewer greenhouse gas emissions.

The Power of 3E Plus®

The 3E Plus® software program from the North American Insulation Manufacturers Association (NAIMA) is an invaluable industrial energy management tool that can be used to calculate energy savings and determine the most energy-efficient use of insulation. It also helps users—including facility managers, energy and environmental managers, industrial process engineers, and industrial plant managers—reduce plant emissions, improve system process efficiency, and determine return on investment (ROI) of insulation upgrades.

3E Plus is designed to allow users to calculate heat losses and determine surface temperatures on hot and cold piping, as well as equipment. The program can:

• calculate the thermal performance of both insulated and uninsulated piping, ducts, and equipment;
• translate British thermal unit (Btu) losses into actual dollars; and
• calculate greenhouse gas emissions and reductions.

The latest version of 3E Plus can be downloaded for free at Pipeinsulation.org. The program includes thermal conductivity curves from ASTM Material Specifications for most insulation types. Users have the option of inputting thermal data from other sources, if desired.

Learn how to use 3E Plus effectively by taking the National Insulation Association's (NIA's) Insulation Energy Appraisal Program (IEAP), which is a fully accredited certification program. For more information, please visit www.insulation.org/training/ieap.

NYSERDA Offers Energy-Saving Expertise

The New York State Energy Research and Development Authority (NYSERDA) was established by a 1975 law as a public benefit corporation. It is devoted to using innovation and technology to solve some of New York's most challenging energy and environmental problems in ways that improve the state's economy. NYSERDA offers sophisticated energy-efficient construction advice, services, and funding for new construction and rehabilitation improvements. Its efforts are concentrated largely on improving the environment, especially in relation to the emissions associated with the generation and consumption of energy.

Since 1990, NYSERDA has successfully developed and brought into use more than 170 innovative, energy-efficient, and environmentally beneficial products, processes, and services. It works with hundreds of businesses, schools, and municipalities to identify existing technologies (such as insulation) and equipment to reduce energy costs.

For more information on NYSERDA and its energy-saving efforts, please call 866-697-3732 or visit www.nyserda.org.

Case Study conducted by Michael Lettich. Mike Lettich is the principal consultant of MJL Consulting, where he helps the chemical, petroleum, pharmaceutical, pulp and paper, utility, and other industries improve their maintenance programs. He consults in insulation, coatings, and contractor effectiveness. A chemical engineer, he previously worked for DuPont, from which he retired after 28 years. While at DuPont, he helped implement the Thermal Insulation Maintenance Service® (TIMS®), providing strategic, focused, cost-effective insulation maintenance programs in industry.

Georgia-Pacific Reaps Benefits by Insulating its Steam Lines

Insulation upgrade program reduces fuel costs and increases process efficiency at Georgia-Pacific plant

Built in 1979, the Georgia-Pacific plant at Madison, Ga., uses Loblolly pine to manufacture plywood. The tree is abundant in the area. Most of the trees harvested are within a 180- mile radius of the mill. About 20 percent of the trees are grown on land owned by Georgia-Pacific and about 80 percent come from other privately owned land. The plant runs 24 hours, 7 days a week and employs approximately 400 people.

The process of making the veneer layers in a plywood panel begins when logs arrive at the mill in sections. They are immediately debarked and soaked in water at 180°F for six hours. This softens the logs and enables them to peel better. The softening process also allows the logs to pass through the lathe much easier and delivers the veneer layers at the right temperature to the dryer where they are dried at temperatures of 405°F.

From the dryers, the veneer layers go to the glue line where layers are sandwiched with glue and then pressed into a panel. From there the panels go to the saw line for trimming before banding and shipping.

Because the steam lines to the dryer were uninsulated, heat was radiating out and millions of Btu were being lost. The heat loss resulted in a loss of pressure and a reduction in temperature as the plywood moved down the line. The increased drying time needed slowed the process down significantly.

While Georgia-Pacific wanted to insulate the steam lines for energy conservation, improved process efficiency and personnel protection, the company also wanted the insulation for a more pragmatic reason—to eliminate dependence on purchased fuel. The plant normally uses wood bark and wood byproducts for fuel. However, at certain times of the year the bark is too thin for use as adequate fuel so additional fuel had to be purchased from an outside source.

Determining the Thickness of Insulation

Once the decision was made to insulate the steam lines, a computer program called 3E Plus created by the North American Insulation Manufacturers Association (NAIMA) was used to determine the insulation thickness required to insulate the 1,500 feet of saturated steam lines with temperatures operating at 437°F.

Computer projections estimated that insulation would significantly reduce the heat (Btu) loss along the steam lines leading to the dryers. This reduction in heat loss alone could increase the operating temperature by 15° and maintain the process temperature along the length of the lines. The combination of a higher temperature in the dryer lines and a more consistent process line temperature would result in a faster and more efficient veneer plywood process.

The Madison plant installed two-inch thick fiber glass pipe insulation. Two inches is the thickness needed to reduce heat loss, maintain process temperature and bring the outside surface temperatures of the pipes down for personnel protection. Insulation footage was as follows: 120 feet of insulation on the twelve-inch process line; 200 feet on the eight-inch process line; 220 feet on the six-inch process line; 80 feet on the four-inch process line; and 350 feet on the 1-1/2-inch process line.

A major advantage of using mineral fiber insulation to insulate the steam lines was that no downtime was required. Several areas that could not be insulated while the line was running were insulated on schedule down days. Says Jackson, "We do dryer maintenance once a week so the dryer is shut down during that time. That's when the insulation was installed on those areas that couldn't be accessed while the dryer was running."

Immediate Results

The personnel at the Georgia-Pacific plant were pleased with the results of the insulation project.

Improved Process Efficiency

The lines to the mill's four dryers have all been insulated, and according to Darryl Jackson, boiler superintendent at the Madison plant, "Gauging the increase in throughput has proven to be a bit more complex than we first thought. A more accurate gauge of the effectiveness of the insulation is the steam usage. The insulation has allowed us to cut our steam usage by approximately 6,000 lbs./hour. This is equivalent to saving about 18 tons of fuel per day. I can track these numbers with a totalizer so I know exactly what the dryers are pulling at any given time."

Dependence on Outside Fuel Eliminated

By insulating the piping, Georgia-Pacific has been able to eliminate the purchase of fuel. Says Jackson, "Currently we are selling some of our excess fuel to a paper company."

Reduction in Pollutants

By reducing fuel consumption, the Madison plant has been able to reduce the amount of ash being generated and estimates that the energy saved through insulation has reduced the amount of C0₂ emissions by 5 to 6 percent.

Increased Personnel Protection

Prior to installing the insulation, the piping in the Madison plant had a surface temperature of approximately 400°F. With insulation, the surface temperature has been reduced to approximately 85°F—a safer level for personnel protection.

In addition to insulating the steam lines, Georgia-Pacific also replaced 70 steam traps. According to Jackson, "We've probably gained 10 percent condensate return from replacing the thermal dynamic traps. By increasing the condensate by 10 percent, our savings will be approximately $86,000 per year based on an $8 per ton fuel cost".

Georgia-Pacific estimates that the amount of energy saved by insulating the steam lines to the dryers and installing new steam traps is approximately 7,212,000 Btu per hour.

Payback on Initial Investment

Calculating how long it takes to pay back an initial insulation investment is an integral part of Georgia-Pacific's energy management program. Based on the results realized, the payback period at Madison was approximately six months

This case study appeared in the March 1998 issue of Insulation Outlook, published by the National Insulation Association

Introduction

The Executive House in Chicago is generally known as the first reinforced concrete skyscraper. At the time of it's completion in 1959, it was the tallest reinforced concrete building in the United States at 39 stories, or 371 feet. In 1962, the twin towers of Marina City in Chicago set a new record at 588 ft above grade. These distinctive circular, reinforced concrete towers also served as an early example of a cast-in-place concrete wall system. Subsequently, Chicago's Lake Point Tower built in 1968 and Houston's One Shell Plaza built in 1970 set new records at 645 ft and 714 ft, respectively. While both of the latter buildings are clad in materials other than concrete, their innovative structural systems are reflected in their façades and established the precedent for many of the cast-in-place concrete wall systems seen throughout the United States.

Description

A cast-in-place concrete wall system is an exposed structural system that also serves as the façade. Openings or penetrations in the structural system are generally infilled with windows, masonry, or some other cladding material.

Fundamentals

Cast-in-place concrete wall systems are generally defined by the building's structural system, which consists of the vertical (gravity) load resistant system and the lateral (wind and seismic) resistant system. The vertical load resistant system may be further subdivided into the horizontal framing (floor system) and the vertical framing (column and walls). The lateral resistant system includes moment resisting frames, shear walls, braced frames, or a combination of these systems.

A concrete structure designed and constructed in the United States is governed by the minimum provisions of the ACI Building Code. While most of the design provisions of the Code dictate minimum strength (safety) requirements, the Code also prescribes serviceability and durability requirements. Certain factors which influence the design of the structural system also impact the exterior wall. These factors include deflection, cracking, concrete cover, and corrosion protection.

Performance Issues

Thermal Performance

Cast-in-place concrete walls derive their thermal performance characteristics primarily from the amount of insulation placed in the cavity or within the backup wall.

Moisture Protection

The most common moisture protection system used with cast-in-place concrete wall systems is a barrier system incorporating an adequate joint seal. In some cases where additional moisture protection is needed, the application of a sealer or a concrete coating is also used. Sealers can be either clear or pigmented if used as an enhancement of the precast appearance. Film-forming coatings usually offer a higher level of performance but will have a significant impact on the appearance of the precast concrete unit.

The cast-in-place concrete wall should also be designed to provide the appropriate level of durability for the planned exposure. Durability can be improved by specifying minimum compressive strengths, maximum water to cement ratios, and an appropriate range of entrained air.

Fire Safety¹

At relatively high temperatures experienced in fires, hydrated cement in concrete will gradually dehydrate, reverting back to water (steam) and cement. This results in a reduction in strength and modulus of elasticity (stiffness) of concrete that, in some instances, can result in spalling. The overall fire resistance of concrete is influenced by aggregate type, moisture content, density, permeability, and nominal thickness. "Carbonate" aggregates, such as limestone, dolomite, and limerock, have been found by some to improve the overall fire resistance of concrete due to their ability to absorb some of the heat from a fire. Similarly, concretes with lower unit weights (densities) will also offer improved fire resistance, as will dried light-weight concrete. In contrast, concrete with relatively low moisture content, low water-cement ratio, and highly impermeable concrete may spall when subjected to fire.

¹Gustaferro, Armand H., "Fire-Resistant Concrete", MC Magazine Archive

Acoustics

A cast-in-place concrete wall system and precast concrete panel façade will provide similar performance regarding sound transmission from the exterior to the interior of the building. See Precast Concrete Wall Systems for additional information, as well as the industry and trade association web site links listed at the end of this section.

Material/Finish Durability

The key issue to be addressed in design of a cast-in-place façade element is durability related to environmental exposure such as moisture, carbonation of concrete, and other factors that can contribute to the distress and deterioration of concrete.

Concrete deterioration may occur for two principal reasons: corrosion of the embedded steel resulting in concrete deterioration, and degradation of the concrete itself. Concrete normally offers protection to embedded reinforcing steel through its alkalinity.

Concrete deterioration due to corrosion of embedded steel is usually related to moisture, and is typically in the form of cracking and delamination of the concrete. Where embedded reinforcing steel is not protected by the alkaline environment of the concrete, and the steel is exposed to moisture, corrosion occurs. The corroded steel expands significantly in volume, which results in expansive forces on the adjacent concrete, causing it to crack and spall. This is visually apparent in cracking and delamination of the concrete and rust staining at the location of embedded steel.

Carbonation results in the loss of alkalinity within the concrete to the level of the reinforcing steel. Carbonation normally occurs only in the vicinity of the exposed surface of the concrete, but in some cases may extend to the level of the steel. Once this occurs, the concrete offers no protection to the embedded reinforcing steel, and corrosion begins. Carbonation occurs from a combination of moisture and carbon dioxide.

Corrosion of embedded reinforcing steel is often due to calcium chloride added to the concrete as an accelerator during original construction or later from de-icing salts used in northern climates. Chloride ion in combination with moisture results in corrosion of the embedded steel and resulting deterioration of the surrounding concrete. Sea water, or other marine environments, provide large amounts of chloride.

The exposed surface of the concrete is also vulnerable to weathering from the elements. This may typically be observed as erosion of the concrete paste. Especially in northern regions where precipitation has been found to be highly acidic, exposure has resulted in more significant erosion of the paste on the exposed surfaces.

Freeze-thaw damage results from the freezing of concrete that is saturated with water. This type of damage appears as degradation of the surface, including severe cracking, extending into the concrete. It was accidentally discovered that portland cement concretes that incorporate microscopic air bubbles provided resistance to cyclic freezing and thawing. The air-entrainment provides "relief valves" that protect the concrete. Air-entraining agents are now generally (but not always) added to cement or concrete used in exposed applications that are in areas of the United States subject to sub-freezing temperatures.

Alkali-aggregate reactions result when alkalis normally present in cement react with silicious aggregates in concrete that is exposed to moisture. The reaction produces a toothpaste-like gel that develops over years or decades until the forces created expand and crack the concrete. Most such deleterious aggregates can be detected by experience or test, and low-alkali cements can be used in new construction to prevent significant reactions.

Sulfate attack is produced by the reaction of excessive amounts of sulfate salts with cement components that are exposed to moisture. The reaction leads to the development of expansive forces that eventually crack the concrete. The sulfate salts may come from the environment (e.g., sulfate waters or solids), or from one or more of the concrete constituents (e.g., aggregates, cement, or proprietary product providing fast set).

Other forms of concrete deterioration exist, including freeze-thaw damage, alkali-aggregate reaction and sulfate attack, but less common in cast-in-place concrete wall systems.

Maintainability

Durability of concrete and resistance to deterioration is dependent on durability, proper design, and good workmanship. This will also be true for the materials used to repair existing concrete. A mix design for durable replacement concrete should utilize materials similar to those of the original concrete mix and include air-entrainment, appropriate selection of aggregates, and adequate cement and water content. Good workmanship should address proper mix, placement, and curing procedures. In all cases, a good mix design will enhance good workmanship for durable repair concrete.

In designing repairs to existing concrete, parameters must be established to define the goals of the project based on visual evaluation and laboratory studies. A key concern is the aesthetics of the repair, to match the existing concrete as closely as possible both visually and structurally. Another governing concern is to select repair interventions that retain as much as possible of the original material; however, an adequate amount of distressed concrete must be removed to provide a durable repair.

All repairs of existing concrete require proper preparation of the substrate to receive the repair material. This typically includes sandblasting, airblasting, or other appropriate means to provide a clean surface to which the repair can adequately bond. Bonding agents are commonly used on the substrate surface to enhance the bond of the repair. Existing reinforcing steel that is exposed during the repair may require cleaning, priming, and painting with a rust-inhibitive coating. In most cases, the repair area should be reinforced and mechanically attached to the existing concrete. Reinforcement may be regular steel, epoxy-coated steel, or stainless steel, depending on the conditions.

Proper placement and finishing of the repair is important in achieving a match to the original concrete. Appropriate curing is essential for a durable repair; wet curing is recommended to reduce the time of curing and the potential for surface and shrinkage cracking.

The preparation of trial repairs and mockups to refine the repair design, and also to evaluate repair procedures is a wise procedure. Mockups also permit evaluation of the visual and aesthetic acceptability of the repair design.

Because concrete deterioration is primarily the result of moisture penetration, rehabilitation may also entail application of a decorative surface coating or clear penetrating sealer. These water-resistant coatings and sealers should be breathable and alkali-resistant.

Various repair methods and techniques are available in the market today to reduce the rate of corrosion of embedded reinforcing and associated deterioration of the concrete. One method is cathodic protection, which utilizes an auxiliary anode so that the entire reinforcing bar is a cathode. (Corrosion is an electro-chemical process in which electrons flow between cathodic (positively-charged) and anodic (negatively-charged) areas on a metal surface; the corrosion occurs at the anodes.) Cathodic protection is intended to reduce the rate of corrosion that occurs to embedded steel in concrete, which in turn reduces concrete deterioration.

Cathodic protection is only one of many evolving techniques available to protect concrete. Another technique currently available is realkalization, which involves returning the concrete to its natural alkaline state.

Applications

Cast-in-place concrete wall systems have been in use in the United States for many decades. Much of the early development of this construction type occurred in Chicago, primarily due to the influence of the Portland Cement Association and innovative structural engineers like Fazlur Khan. The permanence of this building type is evident by the number of prominent cast-in-place concrete buildings built in the 1950's and 1960's that still exist and remain functional today.

See Appendices for climate-specific guidance regarding building enclosure design.

Emerging Issues

Ordinances related to the maintenance of façades, including cast-in-place concrete wall systems, have been enacted in New York and Chicago. As the inventory of older buildings increases, the maintenance of these building façades and the life safety issues associated with their deterioration will also increase.

The mechanisms that generally contribute to the deterioration of cast-in-place concrete wall systems are well known. Improvements in design standards and repair technology will result in improved performance.

The necessity to make building envelopes blast-resistant has forced reconsideration of the cast-in-place concrete façade as a design option.

Relevant Codes and Standards

• American Concrete Institute ACI 318—Building Code Requirements for Structural Concrete
• American Concrete Institute ACI 301—Specifications for Structural Concrete
• Concrete Reinforcing Steel Institute (CRSI)—Reinforced Concrete Fire Resistance

Additional Resources

WBDG

Products and Systems

See appropriate sections under applicable guide specifications: Unified Facility Guide Specifications (UFGS), VA Guide Specifications (UFGS), DRAFT Federal Guide for Green Construction Specifications, MasterSpec®

Publications

• Concrete Homes Magazine

Organizations

• American Concrete Institute (ACI)
• Autoclaved Aerated Concrete Product Association (AACPA)
• Concrete Reinforcing Steel Institute (CRSI)
• Concrete Homes Council
• Insulated Concrete Forms—EPS Industry Alliance
• Portland Cement Association (PCA)

Other

• Spray-Applied Concrete Wall Systems

Introduction

The design and construction of safe and secure buildings continues to be the primary goal for owners, architects, engineers, and project managers. Security and safety measures, such as those for anti-terrorism and force protection (ATFP), must be considered within a total project context, including impacts on occupants and the environment, regardless of the level of protection deemed appropriate. This includes the consideration of impacts to the facility HVAC systems in general, and those systems interacting with the building envelope specifically. Of particular concern are airflow patterns and dynamics both inside and outside of buildings, especially pertaining to the internal release or external release of chemical, biological or radiological contaminant, and the measures necessary to limit airborne contamination.

Description

The main objectives of Chemical/Biological/Radiological (CBR) safety and protection are to provide building systems and controls that provide a safe and secure indoor environment in the event of a CBR release inside or outside of the building.

Because of the fairly recent attention to this topic the definition of what constitutes safe and secure building systems and controls is evolving, there are several fundamentals that should be implemented.

• Provide a Tight Building Envelope — A tight building envelope can significantly reduce the entrainment of CBR agents in to the building through careful control of infiltration.

• Incorporate Dedicated Ventilation and/or Exhaust Systems — Dedicated ventilation and exhaust systems located on roofs or high above grade level are easier to keep secure from CBR release and entrainment.

• Use Dedicated HVAC Systems for Perimeter Zones — Dedicated HVAC systems serving perimeter zones adjacent to building envelopes enhance the control of positive building pressurization and CBR mitigation.

• Evaluate the HVAC System Controls — HVAC system controls should have the ability to monitor outdoor air intakes for the presence of chemical agents but should also provide emergency shutoff and control.

• Consider the Physical Security of HVAC Components — HVAC equipment and outdoor air intakes should be physically secure from tampering and the potential release of CBR agents in close proximity.

• Incorporate Higher Levels of Filtration — While not specifically impacted by the design of the building envelope, the filtration provided as part of the HVAC system can help protect a building in the event of a CBR agent release.

Fundamentals

Provide a Tight Building Envelope

Figure 1. Air Leakage through a Building Enclosure

In traditional construction, infiltration occurs through gaps and cracks in the building envelope. Excess infiltration of cold air in the winter and hot humid air during the summer can create uncomfortable indoor environments and raise heating and cooling costs by 20% to 40%. Such unintentional infiltration is also a concern for an exterior chemical, biological, and radiological (CBR) release at some distance from a building, such as a large-scale attack. Decreasing infiltration improves comfort, saves energy, controls moisture, reduces indoor pollution, and makes forced ventilation necessary. Also, tight building construction in combination with building pressurization can be an effective CBR-protection strategy.

Commission Envelope Elements—the building commissioning process should include commissioning of the building envelope to insure that all performance requirements are being met. Commissioning of the building envelope can identify areas of concern related to air infiltration and leakage, moisture diffusion, surface condensation, and rain water entry—all issues that can negatively impact the building's energy performance and indoor environmental quality. Of particular importance is to begin commissioning of the building envelope during design when design modifications can be easily incorporated, rather than waiting until construction when remediation can cost significantly more.

While the LEED® Green Building Rating System requires buildings to undergo Fundamental Building Commissioning of systems to achieve certification, it merely recommends that some form of building envelope commissioning be incorporated. Lemieux and Totten have proposed a Building Envelope Commissioning process that could supplement the Fundamental Building Commissioning required for LEED® certification.

Incorporate Dedicated Ventilation and/or Exhaust Systems

Exposure of building occupants to potentially hazardous chemical, biological, and radiological (CBR) agents negatively impacts the indoor environment and can pose serious health threats. To help maintain superior indoor air quality and protect people's health, dedicated ventilation systems (aka. dedicated outdoor air systems [DOAS]) and dedicated exhaust systems can be installed. DOAS use separate air handlers to condition and deliver the minimum required constant volume of outdoor air. Be sure to protect all outdoor air intakes and locate away from all exhaust openings. For more information, see the Department of Health and Human Services Guidance for Protecting Building Environments from Airborne Chemical, Biological, or Radiological Attacks, May 2002 and Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, April, 2003.

Use Dedicated HVAC Systems for Perimeter Zones

Provide dedicated HVAC systems to serve perimeter zones and maintain positive pressurization with respect to the building envelope. This strategy will help mitigate external and internal release of chemical, biological and radiological contamination.

Evaluate the HVAC System Controls

Figure 2. Ion Mobility Spectrometry (IMS) chemical detector designed for installation in HVAC Systems Courtesy Smiths Detection

Many HVAC systems incorporate energy management and control systems that can regulate air flows within a building on an emergency response basis. Consider utilizing the control system for this purpose. In some cases, simply shutting off the building's HVAC and exhaust systems might be the most effective means of avoiding introducing a CBR agent from outside the building. In other cases, pressurization and airflow control between zones within a building may be effective in minimizing the spread of a CBR agent released within the building. This strategy should include consideration of using pressure sensors inside and outside the building (and between zones) to measure pressure levels and control HVAC equipment to maintain pressure relationships.

If an HVAC control plan is pursued, building personnel should be trained to recognize a terrorist attack quickly and to know when to initiate the control measures. All procedures and training associated with the control of the HVAC system should be addressed in the building's emergency response plan.

Consider the Physical Security of HVAC Components

Figure 3. Protecting Outdoor Air Intakes Courtesy of Guidance for Protecting Building Environments From Airborne Chemical, Biological and Radiological Attacks, NIOSH

Outdoor Air Intakes—One of the most important steps that can be taken to protect a building's indoor environment from CBR attack is the security of outdoor air intakes. Introducing CBR agents into outdoor air intakes allows for the dispersion throughout the building via the HVAC system. Intakes at or below grade are most at risk due to their accessibility and because most CBR releases will be near the ground and remain there. Locate outdoor air intakes above the third floor of the building, and preferably at roof level whenever possible.

Figure 4. Vulnerable Outdoor Air Intakes Courtesy of Guidance for Protecting Building Environments From Airborne Chemical, Biological and Radiological Attacks, NIOSH

Rooftop HVAC Equipment—Roofs are similar to other entrances of a building and should be physically secured. Since HVAC equipment, including air handling units and their outside air intakes, are often located on rooftops and are susceptible to CBR attack, it is especially important to restrict access to the roof.

Figure 5. Example of Rooftop HVAC Equipment

Incorporate Higher Levels of Filtration

Filtration—This is an overall HVAC system issue, not only specific to the Building Envelope Design Guide. Please refer to BIPS 06 / FEMA 426 Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings for a thorough discussion of filtration for CBR mitigation. Some consideration should also be given to the associated energy cost impact of installing the additional filtration equipment. Energy simulation and life cycle analysis tools can and should be used to assess the energy cost impacts.

Applications

The CBR Safety fundamentals previously described should be considered for and applied to the building envelope design and construction, and to HVAC systems interacting with the building envelope, for all buildings.

Related Issues

Balancing Security/Safety and Sustainability Objectives—Providing for sustainable designs that meet all facility requirements is often a challenge to the building design, construction and operation community. With limited resources it is not always feasible to provide for the most secure facility, the most architecturally expressive design, or energy efficient building envelope. From the concept stage through the development of construction documents, it is important that all project or design stakeholders work cooperatively to ensure a balanced design. Successful designs must consider all competing design objectives.

Integrated Design—Designers are moving away from the conventional building design approach that has historically resulted in little interaction between all parties involved in the project. There is a movement to embrace integrated building design, fostering communication amongst all parties that could be involved in the project, and facilitating working together from the start to coordinate and optimize the design of the site and the building.

Relevant Codes and Standards

Federal Mandates

• Executive Order 12977, "Interagency Security Committee"—Interagency Security Committee (ISC) Security Design Criteria-unites all Federal protective design requirements (For Official Use Only)
• Executive Order 12656, "Assignment of Emergency Preparedness Responsibilities"

Standards and Guidelines

• UFC 4-010-01 DoD Minimum Anti-Terrorism Standards for Buildings, U.S. Department of Defense
• Guidance for Protecting Building Environments from Airborne Chemical, Biological, or Radiological Attacks by the National Institute for Occupational Safety and Health (NIOSH)
• Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks by the National Institute for Occupational Safety and Health (NIOSH)
• PBS-P100 Facilities Standards for the Public Buildings Service, General Services Administration
• BIPS 06 / FEMA 426 Reference Manual to Mitigate Potential Terrorist Attacks Against Buildings by the Department of Homeland Security
• FEMA 427 Primer for Design of Commercial Buildings to Mitigate Terrorist Attacks

Additional Resources

Federal Agencies

• Centers for Disease Control and Prevention (CDC)
• Department of Homeland Security (DHS)
• Federal Emergency Management Agency (FEMA)
• Federal Facilities Council (FFC) Standing Committee on Cyber and Physical Security and Hazard Mitigation

Publications

• Building Ventilation and Pressurization as a Security Tool, Andy Persily, ASHRAE Journal, September 2004.
• Building Security Through Design: A Primer for Architects, Design Professionals, and their Clients, The American Institute of Architects, Washington DC, 2001
• Protection of Federal Office Buildings Against Terrorism, Committee on the Protection of Federal Facilities Against Terrorism, Building Research Board, National Research Council, Washington DC, National Academy Press, 1988.
• Uses of Risk Analysis to Achieve a Balanced Safety in Building Design and Operations, by Bruce D. McDowell and Andrew C. Lemer, Editors; Committee on Risk Appraisal in the Development of Facilities Design Criteria, National Research Council, Washington DC, National Academy Press, 1991.

Organizations

• American Society of Civil Engineers (ASCE)
• American Society of Industrial Security (ASIS)
• Protective Glazing Council (PGC)
• Society of American Military Engineers (SAME)

Overview

The Child Care space types, described herein, are the facilities required for child care services permitted within federal facilities. The intention of high quality federal child care is to allow employees to respond to their dual work and family responsibilities effectively to the benefit of both families and the government as employer. A licensed child care center is a facility, other than a private residence, approved and licensed by a state or other applicable local authority where a person, other than a relative or guardian, is compensated to provide care and supervision for 4 or more children under 7 years of age for less than 24 hours a day. A "small" center is one which is licensed for less than 60 children, while a "large" one is licensed for more than 94 children. Child Care space types include additional support and space sub-types, including toilets, food preparation and service, office space, and meeting space, as well as security features required in compliance with codes and regulations.

Space Attributes

Child Care spaces should be secure environments that provide a variety of learning experiences and meet the physical needs of the children. See WBDG Child Development Centers for more information on the unique attributes of spaces designed for child development and care. Typical features of Child Care space types include the list of applicable design objectives elements as outlined below. For a complete list and definitions of the design objectives within the context of whole building design, click on the titles below.

Accessible

• Child care center design must comply with the Americans with Disabilities Act (ADA). The design must accommodate children and adults with disabilities. The site, as well as the building access to and within the child care spaces, shall comply with the current publication of the Uniform Federal Accessibility Standards (UFAS), the final rules of the Americans with Disabilities Act Accessibility Guidelines (ADAAG), and local accessibility codes, whichever is most stringent.

Accessible swing for wheelchair users. Photo Credit: kaboom.org

Functional / Operational

• Classrooms are the architecturally defined areas that contain each group of children. Classrooms may be separated by full partitions or by partial barriers that also allow controlled visual or acoustical connections to other groups.

• Design spaces with a sensitivity to children's scale, including how they will use the space, what they will see, and what kind of experience they will have.

• Classroom equipment and durable goods including cots and cribs, chairs and other seating devices, furniture, play equipment, academic equipment, presentation equipment, audiovisual equipment, computer equipment, food service, and hygiene equipment must be provided. Provide durable and cost-effective materials and details. This is vital when the designer considers the intensity of use that a center receives. Particular sensitivity should be paid to the life-cycle cost of materials.

• Outdoor spaces may include play yard space, including fencing, canopy, sidewalk, ground cover, drainage, shade devices, play structures, and vegetation planting. See WBDG Playground Design and Equipment for more information.

Occupancy: Occupancy Group Classification is Educational Occupancy E as sub-occupancy with Business B2 Building Occupancy, with sprinklered construction. See also WBDG Secure / Safe—Fire Protection.

Productive

• Office space in Child Care space types should be equipped with infrastructure to support telephone and data communication systems including space, power, and conduit and telephone and data communication equipment.

• Consider providing on-site food service areas directly serving the daycare population and on-site laundry services and water services including hot water and water conditioners.

Secure / Safe

• Whenever possible, design the space to prevent direct access to the child care area. Instead, create a secure main entrance which will be separated from the doors to individual child care rooms and spaces so that a person entering may need to go down a hallway or around a corner to get to a child care entrance.

• Security equipment for Child Care space types may include access control, intrusion detection, and alarm systems. See also WBDG Secure / Safe—Security for Building Occupants and Assets.

• Additional elevators and exit stairways may be required for Child Care spaces located on the 2nd level of buildings.

• Ensure that there is adequate exterior lighting to allow safe exterior circulation and site security.

Sustainable

• Provide ample natural light in all spaces where children will spend time, especially the classrooms.

• Minimize energy use. Also consider placement of mechanical equipment to ensure energy efficiency as well as acoustic comfort and control.

• Equipment, furnishings, and finishes must be non-toxic and not contain asbestos, lead, or other VOCs.

• Equipment, furnishings and finishes should be cleaned and maintained using sustainable cleaning or improved maintenance practices.

• Good indoor air quality must be provided.

• See also WBDG Secure / Safe—Occupant Safety and Health

Example Program

The following building program is representative of Child Care center space types and is based on the ratios prescribed in the PBS-140 Child Care Center Design Guide. The center described below included provisions for 86 children.

CHILD CARE

Example Plans

The following diagram is representative of typical tenant plans.

Example Construction Criteria

For GSA, the unit costs for child care space types are based on the construction quality and design features in the following table . This information is based on GSA's benchmark interpretation and could be different for other owners.

Relevant Codes and Standards

The following agencies and organizations have developed codes and standards affecting the design of child care centers. Note that the codes and standards are minimum requirements. Architects, engineers, and consultants should consider exceeding the applicable requirements whenever possible.

• ADA Standards
• Energy Policy Act of 2005 (EPACT)
• Executive Order 13101, "Greening the Government Through Waste Prevention, Recycling, and Federal Acquisition," September 14, 1998.
• Executive Order 13148, "Greening the Government through Leadership in Environmental Management," June 1999.
• GSA PBS-140 Child Care Center Design Guide
• GSA PBS-P100 Facilities Standards for the Public Buildings Service
• Interagency Security Committee (ISC) Security Design Criteria—Contains specifications pertaining to window protection in child care centers located in GSA controlled facilities. (For Official Use Only)
• ICC IBC International Building Code
• U.S. Access Board, Play Area Guidelines

Additional Resources

Organizations and Associations

• Building Child Care in California—This project exists to provide a centralized clearinghouse of information and services designed to improve child care providers' access to financial resources for facilities development projects in California.
• National Resource Center for Health and Safety in Child Care and Early Education—The NRC's primary mission is to promote health and safety in out-of-home child care settings throughout the nation.

Publications

• Architectural Graphic Standards, 12th Edition by American Institute of Architects, Dennis J. Hall. New York, NY: John Wiley & Sons, Inc., 2016.
• Children, Youth and Environments, CYE is a refereed journal and multidisciplinary, international network dedicated to improving the lives of young people. The journal targets researchers, policy makers, and professionals and is guided by a distinguished Editorial Advisory Board.