Volume 7 Issue 1 January 2006
Updated Weatherstrip Standard
Ensuring An Optimum Trade-off
by Dean Lewis
For product certification to be an effective indication of performance quality, it—and the performance standards upon which it is based—must go beyond testing completed window units and treat a window as a complex system of components. One of these components is weatherstripping, which affects a variety of performance factors including air infiltration, water-tightness and operating force.
In order to be certified for conformance to the current window standard, under the AAMA Certification Program, AAMA/WDMA/CSA 101/ I.S. 2/A440-05, weatherstripping must meet minimum requirements for two primary attributes: weatherability and compression set.
Those requirements, and test methods for determining if they are met, are spelled out in AAMA 701/702-04, a standard covering the testing of pile weatherstripping (701) and replaceable fenestration weatherseals (702). The standard recognizes that fenestration products interact with sealing systems in two ways: 1) user stresses induced by repeated opening/closing of sash or panels, and 2) environmental weathering due to heat, UV radiation and moisture. These elements induce physical, chemical and thermal stresses on weatherseals that can affect their durability and long-term reliability.
The 701 section of the AAMA standard for pile weatherstripping requires two basic tests for certification approval:
• Accelerated Weathering/ Shrinkage Test
The weatherstripping is exposed to a minimum of 288 total hours of cyclic light exposure at 120°F and dark exposure at 113°F, then measured and visually checked for cracking, brittleness, color fade or other observable change in physical integrity. Shrinkage as a percentage of overall length must not exceed 1 percent or 5 mm (0.06 inches).
• Compression Set Test
Using the same compression apparatus, samples are compressed to 75 percent of overall height in a cold (0°F) environment for four hours, then in a hot environment (160°F) for 16 hours. To pass the test, the dry pile must recover to at least 86 percent of its original overall height.
In the AAMA Certification Program, manufacturers may substitute weatherstripping differing in nominal height from that used in the tested sample by maxima of + 0.5 mm (0.02 inches) or - 0.3 mm (0.01 inches) without retesting or obtaining a waiver of retest.
The 702 section of the AAMA document for replaceable fenestration weatherseals applies essentially the same tests to weatherseals to door and window products by means of kerfs, t-slots, pockets or other similar retaining profiles. Performance requirements include the following:
• Compression Set Test
The loss of functional height (that portion of the seal profile that extends above the retaining groove) cannot exceed a range of values according to defined performance classes from less than 10 percent up to 25 percent.
• Weatherability Test
Lineal shrinkage cannot exceed percentages set forth by performance class, ranging from 1 to 4 percent, and no specimen can exhibit brittleness, cracking, profile change, loss of finish or material degradation.
AAMA 701/702 also recognizes that the predominant factor affecting the operating force of hung or horizontal sliding sash is the frictional force between the weatherseals and the frame. As these weatherseals are compressed, they exert a force perpendicular to the frame, resulting in friction that must be overcome to operate the sash. Static friction must be overcome to set the sash in motion and sliding friction must be overcome to maintain motion. There is a trade-off between air infiltration and water penetration resistance and operating force that designers must consider.
The 701/702 standard provides a test method to determine these frictional forces. The test, per ASTM D 1894, is not a pass/fail test, but produces data relating the frictional force to the compression height of the weatherseal at a percentage of compression from its original height.
Weatherseal manufacturers are keenly aware of these factors and have incorporated improved designs, materials and test methods in the development of sealing systems. AAMA certification and the component verification performance standards for weatherseals and other components will help ensure that specifiers and end users are getting one of these preferred solutions.
Dean Lewis serves as manager, product certification, for the American Architectural Manufacturers Association in Schaumburg, Ill. He may be reached at firstname.lastname@example.org.
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