Holes in exterior walls enclosed with windows, doors, and other related components must be integrated with surrounding building envelope components to effectively separate the outdoor environment from interior conditioned space. At the most basic level, windows allow natural light into buildings and resist the passage of water and excessive air. Windows also limit sound and heat transfer into and out of buildings and, in some instances, are designed to protect building occupants from forced entry, hurricane-force winds, and/or explosions. Properly functioning windows must allow desirable elements to be transmitted through them (i.e., light) and limit the transmission of undesirable elements (i.e., air and water).
The in-situ performance of windows remains inferior to specified performance criteria in many instances due to inadequate detailing during the design phase, variation of window installation methods, and imperfect jobsite conditions. Air infiltration and water penetration through and around windows are two items commonly impacted by project-specific variables and window installation practices.
The American Architectural Manufacturers Association/Window and Door Manufacturers Association/Canadian Standards Association’s (AAMA/WDMA/CSA’s) 101/I.S.2/A440, North American Fenestration Standard/Specification for Windows, Doors, and Skylights (NAFS) is mandated by several modern building codes. Although a revised version of NAFS is anticipated to be published in 2017, the 2011 version is currently referenced in the 2015 versions of the International Building Code (IBC 2015) and International Residential Code (IRC 2015).
As defined within NAFS, window Performance Class roughly describes the likely target application for installed window products, ranging from single-family residential to high-rise commercial buildings. Current NAFS 2011 Performance Classes include R, LC, CW, and AW (Figure 1).
Performance Grade is a numeric designator that defines a set of performance requirements for a specific design pressure range. A window product achieves a Performance Grade designation upon successfully completing all applicable tests, primarily those for structural performance and resistance to air infiltration and water penetration. These required tests are performed on prototype window specimens in a controlled laboratory environment.
NAFS 2011 requires air infiltration testing to be performed in accordance with ASTM E283, Standard Test Method for Determining Rate of Air Leakage through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen; and water penetration testing to be performed in accordance with ASTM E547, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Cyclic Static Air Pressure Difference; and/or ASTM E331, Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference. Prototype test specimens are installed plumb, level, and square in a precise test buck opening in strict accordance with manufacturers’ instructions. The required laboratory tests are used primarily to evaluate the performance of the fenestration product and are not intended perimeter seals.
Clearly, laboratory tests used to validate product performance ratings cannot account for excessive air infiltration and/ or water penetration through or around inservice windows as a result of project specific conditions or substandard installation practices. Even if installed in general accordance with manufacturer instructions and industry standards, in-service products are unlikely to find such ideal conditions as during laboratory testing. Handling prior to and during installation, acts of subsequent trades, and environmental conditions may
all adversely affect installed product performance compared to published laboratory test results.
Window performance requirements are typically included in Part 2 – Products of the applicable project specification section. In addition to items related to thermal performance and sound transmission, window Performance Class and Performance Grade are typically specified (Figure 2).
Taken together, specifying the Performance Class and Performance Grade for windows provides a baseline for air infiltration and water penetration resistance requirements. However, since those requirements are not explicitly specified, some ambiguity regarding performance requirements remains. The following questions, among others, would remain unanswered:
- What is the maximum allowable air leakage at the specified positive test pressure? Although NAFS 2011 prescribes maximum allowable air leakage values for various products in different Performance Classes, actual performance of similar fenestration products can vary considerably.
- What is the specified water penetration test pressure? The Performance Grade rating for a product is sometimes limited by structural performance rather than water penetration resistance performance. In these cases, the tested specimen might have successfully passed a water penetration test at a pressure significantly greater than the minimum specified for the Performance Class and Performance Grade.
- What if mulled units are required for the project? Assemblies of two or more individual window units combined in the field without the manufacturer’s involvement are typically not covered by NAFS 2011. Mulled units can either be tested as combination assemblies or with mullion performance tested separately in accordance with AAMA 450, Voluntary Performance Rating Method for Mulled Fenestration Assemblies.
- Is excessive deflection of window frame members a serviceability concern for the project? Deflection is not limited by NAFS 2011 for Performance Class R and LC windows. The project team should adequately address these items during the design phase, and include appropriate accompanying installation and field quality control requirements within the specifications.
ASTM E2112-07 (2016), Standard Practice for Installation of Exterior Windows, Doors, and Skylights, is a consensus document maintained by ASTM International (ASTM). It acknowledges that window installation can significantly influence in-service performance of the units. Although ASTM E2112-07 (2016) defers to window manufacturers for product-specific installation instructions, it remains the default voluntary standard in cases where specific manufacturer recommendations are insufficient or otherwise not available. The document includes much useful information regarding the use of pan flashings, integration of weather-resistive barriers with flanged windows, and window installation best practices in wood-frame buildings (Figure 3), but it is not intended to be used as a project-specific resource. Stated within, the document is “intended to provide technical guidance to organizations that are developing training programs for installers of fenestration units in low-rise residential and light commercial structures.”
Window installation requirements are typically included in Part 3 – Execution of the applicable specification section (Figure 4). Although well-intended, typical specification language
often does not provide adequate window installation guidance. Drawings (and subsequent shop drawings) and specifications must clearly and definitively provide installation instructions to answer the following questions:
- How must windows be anchored to resist code-prescribed loads?
- How will windows be mulled to resist code-prescribed loads, and how will mulls resist air infiltration and water leakage?
- What sequencing will result in proper flashing and integration with adjacent exterior wall components and flashings?
- Are pan flashings or subsills required, and if so, how should they be configured?
- What tolerances are allowable to account for imperfections or out-of-plumb fenestration openings?
The project team must clearly address these potentially unanswered questions prior to window fabrication, as relying on industry guidance and manufacturers’ written instructions alone will typically not be sufficient. Preparing sequencing diagrams is a useful tool to resolve how many building components interface (Figure 5).
FIELD QUALITY CONTROL REQUIREMENTS
AAMA 502-12, Voluntary Specification for Field Testing of Newly Installed Fenestrations, is a consensus document maintained by AAMA. The AAMA 502-12 voluntary specification is used to verify air infiltration resistance performance and water penetration performance of newly installed window products.
Performing field quality control testing early during the project can prove beneficial in identifying window-related issues before they become overwhelming (Figures 6 and 7). Remedial work, if required, will be easier to implement early during a project than if the building has been substantially completed and is occupied.
Field quality control requirements for windows are typically included in Part 3 – Execution of the applicable specification section (Figure 8). Project specifications requiring windows
to be tested for air infiltration and water penetration resistance according to AAMA 502-12, without inclusion of any additional project specific requirements, stipulate the following:
- Three readily accessible windows shall be tested at locations chosen by the architect or owner’s representative.
- Field test pressure for air leakage resistance tests shall be the same as laboratory test pressure designated in NAFS 2011. Allowable rate of air leakage during field testing shall be 1.5 times the applicable NAFS 2011 laboratory rate.
- Field test pressure for water penetration resistance tests shall be performed at a static test pressure equal to two-thirds of the laboratory test pressure designated in NAFS 2011.
- Windows that do not pass air leakage and water penetration tests shall be repaired and retested. Remaining windows throughout the building shall be randomly checked for similar issues.
- An AAMA-accredited independent testing agency shall perform testing. Specifications that solely reference AAMA 502-12 do not completely indicate requirements for quality control testing of installed windows.
The following questions, among others, would remain unanswered:
- What specimens should be tested if there are several different window types and/or configurations at the building?
- Is the one-third reduction in test pressure for field testing a reasonable adjustment to account for variations inherent in a field test environment?
- Are additional tests required if retests of failed windows are also unsatisfactory?
- What entity is responsible for costs associated with additional testing and indirect costs associated with project delays?
- Does the owner have recourse in the case of continual window testing failures?
- What if no local AAMA-accredited independent testing agencies are available to perform the testing?
The project team must clearly address these potentially unanswered questions before field testing commences.
DESIGN CONSIDERATIONS TO IMPROVE IN-SERVICE WINDOW PERFORMANCE
Current building codes and industry standards include several significant informational holes and gaps regarding window performance, installation, and field quality control requirements. Careful detailing during the design phase and quality installation practices will improve the likelihood of acceptable in-service window performance. Inclusion of appropriately robust field quality control requirements within the project documents will likely also prove beneficial. Designers can take several steps during the design phase to increase the likelihood of satisfactory performance of window units during their service life:
- Ensure continuity of air, vapor, water, and thermal barriers. Simple sketches can be used during design development to verify continuity of the various barriers (Figure 9).
- Design pan flashings with properly sized upturned rear legs and end dams. Ensure details clearly illustrate how pan flashings integrate with air, vapor, water, and thermal barriers.
- Drawings should be used to depict illustrative and quantitative project requirements. Specifications should be used primarily to indicate qualitative requirements. Thicknesses and configurations of materials and integration with surrounding construction are most appropriately shown on project drawings.
- Consider the use of isometric details to illustrate conditions that cannot be depicted on two-dimensional drawings. Isometric details can be easily created in Sketchup or a similar graphical program by a qualified technician. These details can be exported to CAD or Revit® and be incorporated into the project drawings.
- Include sequencing diagrams and/or interface drawings indicating substrate preparation; installation of the air, vapor, water, and thermal barriers; pan flashings; window installation; head and jamb flashings; etc. Such diagrams are best suited to be shown in isometric views.
- Consider specifying factory-mulled units to the greatest degree possible. Windows can typically be shipped in large sizes with individual units mulled together to fit in a single fenestration opening.
- Specify requirements for installation to the greatest degree practical. For projects where a window manufacturer has been selected in advance or the specifications include only a single product, provide accurate graphical depictions indicating installation requirements. The window manufacturer can be consulted regarding the use of strap anchors, through-jamb fastening requirements, etc. before project drawings and specifications are complete.
- Specify field-constructed mock-up windows to be tested for air infiltration and water penetration resistance. Ideally, mock-up windows will satisfactorily pass required tests before the remaining windows for the project are procured. Project participants, including the designer-of-record, exterior wall consultant, manufacturer’s technical representative, and general contractor should be present with the installer during mock-ups. Minor adjustments associated with window sizes and/or configurations can thus be made before the remaining windows are fabricated.
- Clearly specify field quality control requirements, including quantity and types of windows to be tested, locations of windows to be tested, requirements for air leakage resistance testing, requirements for water penetration resistance testing, procedures subsequent to failed tests, and qualifications for the testing agency (Figure 10).
AAMA/WDMA/CSA 101/I.S.2/A440-11, North American Fenestration Standard/ Specification for Windows, Doors, and Skylights (NAFS). 2011.’
AAMA, Schaumburg, IL. AAMA 502-12, Voluntary Specification for Field Testing of Newly Installed Fenestration Products. 2012, AAMA, Schaumburg, IL. AAMA 450-10, Voluntary Performance Rating Method for Mulled Fenestration Assemblies. 2010, AAMA, Schaumburg, IL.
AAMA WSG-11, Window and Door Selection Guide. 2011, AAMA, Schaumburg, IL.
ASTM E283-04 (2012), Standard Test Method for Determining Rate of Air Leakage through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen. 2012, ASTM International, Conshohocken, PA.
ASTM E331-00(2009), Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform Static Air Pressure Difference. 2009, ASTM International, Conshohocken, PA.
ASTM E547-00(2009), Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Cyclic Static Air Pressure Difference. 2009, ASTM International, Conshohocken, PA.
ASTM E783-02(2010), Standard Test Method for Field Measurement of Air Leakage Through Installed Exterior Windows and Doors. 2010, ASTM International, Conshohocken, PA.
ASTM E1105-00(2008), Standard Test Method for Field Determination of Water Penetration of Installed Exterior Windows, Skylights, Doors, and Curtain Walls, by Uniform or Cyclic Static Air Pressure Difference. 2012, ASTM International, Conshohocken, PA.
ASTM E2112-07 (2016), Standard Practice for Installation of Exterior Windows, Doors, and Skylights. 2016, ASTM International, Conshohocken, PA.
Robert Bateman. “A Flash in the Pan – A Field Guide for Windows and Doors,” RCI Interface, April 2010.
CSI SectionFormat™/PageFormat™, 2009. The Construction Specifications Institute, Alexandria, VA.
International Building Code, 2015. International Code Council, Country Club Hills, IL.
International Residential Code, 2015. International Code Council, Country Club Hills, IL.
Patrick Reicher is a senior engineer with Raths, Raths & Johnson, Inc. A licensed structural engineer in the state of Illinois, he has over 11 years of experience in the evaluation and repair design of exterior walls. Reicher is a Registered Exterior Wall Consultant (REWC), Registered Exterior Wall Observer (REWO), Certified Construction Specifier (CCS), and Certified Construction Contract Administrator (CCCA). He also serves on several committees as a professional member of the American Architectural Manufacturers Association (AAMA).
Rebecca Booth is an architectural intern with Raths, Raths & Johnson, Inc. (RRJ). She joined RRJ in 2013 after completing her Master of Architecture degree at the University of Illinois at Urbana- Champaign. Her experience includes façade investigations, condition survey documentation, repair design, construction administration, and litigation support for a range of materials and systems. She is a Certified Document Technologist (CDT) and is the secretary for the Building Enclosure Council – Chicago (BEC-C) Board of Directors.