Skip to main content

The 411 on Fenestration Weathering

Weathering and weatherability: Two sides of the same coin 

Testing for both weathering (appearance) and weatherability (performance) is vital for determining the expected life of a fenestration product.

Weathering is a popular topic in fenestration, but it can be misunderstood because, like every coin, it has two sides. One side, weathering, is the ability of a product to maintain a durable and visually appealing surface after exposure to ultraviolet light, heat, time and moisture. The other side of the coin, weatherability, is the ability of a product to maintain its performance over the expected life of the fenestration product.  


The traditional method of testing weathering involves exposing a surface to the environment and waiting to evaluate the durability through appearance changes and surface defects. Some alternative methods are used to simulate these same exposures in a laboratory, greatly reducing how long it takes to evaluate a product.

Since fenestration products are exposed to external conditions, the Fenestration and Glazing Industry Alliance offers a set of material-neutral finish standards—they are the same no matter the composition of the finishes or how they are applied—that cover both types of weathering tests. Different standards are available for aluminum, fiberglass and vinyl substrates, which can help manufacturers specify the finishes’ minimum performance requirements. Within each of these sets are different requirements for weathering exposure.

  • For aluminum: AAMA 2603, AAMA 2604 and AAMA 2605.
  • For fiberglass: AAMA 623, AAMA 624 and AAMA 625.
  • For vinyl: AAMA 613, AAMA 614 and AAMA 615. 


Testing fenestration for weatherability evaluates resistance to environmental factors like wind and rain. Residential windows are designed to help keep out the elements and all windows are tested to evaluate air, water and structural performance. Customers can check with the manufacturer to see if a sample of the window, door or skylight has been tested to determine if it meets industry requirements for water penetration resistance and air infiltration or exfiltration. These requirements are detailed in AAMA/WDMA/CSA 101/IS2/A440, North American Fenestration Standard/Specification for windows, doors, and skylights.

Air infiltration testing. Although there are exceptions, in general, products must not allow more than 0.1 to 0.3 cubic feet per minute of air to pass through every square foot of the opening the manufactured product fills, under prescribed pressure differences, depending on product type and performance class. This testing is performed with a product sample subjected to constant air pressure to simulate a specified wind pressure, representing a time-averaged weather condition. Note that performance results from a test laboratory may differ from an installed performance level due to variances in installation practices, handling and the degree to which routine maintenance may have been performed.

Water penetration testing. Conducted in much the same manner as air infiltration testing, water penetration resistance testing adds a calibrated spray rack that applies water to the surface of the test specimen product at a rate of 5 gallons per hour per square foot, exceeding any rainfall rate of a typical natural storm. However, this high application rate is intended only to maintain a film of water over the product’s entire surface. It is the air pressure differential, simulating wind pressure, that will force water through any potential leakage points at seals or operating joints of the window.

Depending on the performance class being sought as described in NAFS, the air pressure differential across the product varies from 15% to 20% of the design pressure associated with the product’s performance grade. In the U.S., this pressure is capped at 12 pounds per square foot. The way in which the differential air pressure is applied varies with the performance class. 


Rich Rinka

Rich Rinka

Rich Rinka is the technical manager of fenestration standards and U.S. industry affairs at the Fenestration and Glazing Industry Alliance. He can be reached by email at