Specifying a program for new construction
For most new construction projects, the designer produces contract documents that include a specification section for each fenestration type being used on the project. For example, a specifier may select a window product of appropriate Performance Class and Grade to meet the project performance requirements, including design wind pressures, water penetration resistance, and allowable air leakage.
Window specifications should require a minimum Performance Class and Grade for each window system based on the AAMA 101 rating system once the design loads are determined based on American Society of Civil Engineers (ASCE) 7, Minimum Design Loads for Buildings and Other Structures (e.g. by analytical design or wind-tunnel procedure). The minimum PG-rated pressure must be greater than the code-required design pressure. However, selecting a product exceeding the code minimum requirements in PG may help a specifier achieve higher performance levels in categories such as water penetration resistance, when project performance expectations are elevated and tolerance for water leakage is low.
For simplicity, designers often specify the same optional PG for all windows on a project, based on the most conservative value corresponding to the area of the highest exposure and wind pressure. Performance Class and Grade affect how the windows are tested in the field, including test pressures and test types.
For engineered fenestration products, the specifications can include a performance-based or product-based specification. The former should list all performance requirements required to be met by the provided fenestration system (e.g. structural design pressures, deflection limitations, air infiltration, and water penetration resistance). The provided parameters will be used by the engineer or manufacturer during design or selection of the fenestration system. If using a product-based specification, the architect should include a basis of design product in the specifications that meets the project’s performance requirements. This specified system will be used as the basis for evaluating alternative fenestration systems, if submitted by the contractor.
Field quality control most often includes air infiltration and water penetration resistance tests. Specification sections should include a total number of water penetration resistance and air infiltration resistance tests that must be successful, as well as clarify who is responsible for testing and costs. Typically, an independent third party is hired to conduct testing.
Picking an appropriate field-testing sample size is an important step to learning enough about product performance to understand the likelihood of success while minimizing cost impact to the project. AAMA provides guidelines for how to specify a sample size. The guidelines from each standard are summarized below.
AAMA 502 lists three tests as the default quantity, but states the amount of testing can increase or decrease depending on project size and allowable budget for testing. AAMA 502 references ASTM E122, Standard Practice for Calculating Sample Size to Estimate, with Specified Precision, the Average for a Characteristic of a Lot or Process, for additional guidance on establishing the required number of tests.
AAMA 503 provides a single 9.3-m2 (100-sf) test area as the default specimen, noting it should “include perimeter seals, typical splices, frame intersections, and, if applicable, at least two entire vision lites and two entire spandrel lites containing an intermediate vertical and an intermediate horizontal.” AAMA 503 again states the specimen size depends on the project size and allowable budget for testing. It references ASTM E122 for additional guidance on establishing the required number of tests.
AAMA 501.2 lists a 9.3-m2 (100-sf) test area as the minimum, stating it must include “perimeter caulking, typical splices, frame intersection, and if applicable, at least two entire vision lites and two entire spandrel lites containing an intermediate vertical member and an intermediate horizontal member.”
Sample size should also consider the variety of fenestration types. In the experience of this article’s authors, sample sizes may range from one percent for commercial projects with repetitive window types to approximately four or five percent for a smaller project with more unique fenestration types or configurations. On average, typical test programs may include:
- approximately two percent of the total number of fenestration units according to AAMA 502;
- two percent of the total curtain wall and storefront square footage according to AAMA 503; and
- two percent of the total curtain wall and storefront mullion length according to AAMA 501.2.
For small projects, AAMA’s prescribed minimums may control the sample size.
If possible, the testing sample should incorporate multiple window types, configurations, and installation conditions; it should occur at regular intervals to verify workmanship quality remains consistent throughout the project. Both AAMA 502 and 503 recommend conducting testing as soon as feasible, and at five, 50, and 90 percent completion. Performing testing as soon as feasible helps the project team understand initial performance of the fenestration product prior to wholesale installation (preferably via a mockup before product is delivered to the site). Likewise, testing throughout installation is needed to ensure installation quality remains constant.