A Guide to NAFS Testing

The North American Fenestration Standard (NAFS) for windows, doors, and skylights is a document created by three groups:

 

• FGIA (fka AAMA)

• WDMA (Window & Door Manufacturers Association)

• CSA Group (Canadian Standards Association)

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This standard groups windows, doors, and secondary storm products (SSPs) into four Performance Classes based on their durability and strength:

• R (Residential): Used in single-family and two-family homes.

• LC (Light Commercial): Used in small apartment buildings or low-rise buildings that need stronger windows and doors.

• CW (Commercial Windows): Used in low- to mid-rise buildings where windows and doors need to be larger, stronger, and able to handle frequent use.

• AW (Architectural Windows): Used in high-rise and mid-rise buildings that need the most durable windows and doors, capable of withstanding extreme use and higher wind pressures.

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The six main performance factors tested are:

• Operating force (how easy it is to open and close) – if applicable

• Air leakage resistance (how well it prevents air from passing through)

• Water penetration resistance (ability to keep water out)

• Uniform load deflection test (how much it bends under pressure)

• Uniform load structural test (how much force it can handle without breaking)

• Forced-entry resistance (protection against break-ins) – if applicable

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The Operating Force Test:

Evaluates the amount of force required to initiate and maintain the movement of a window or door through its full range of operation under normal conditions. This includes the effort needed to unlock, open, close, and relatch the product using its standard hardware, such as handles, cranks, or sliding mechanisms. The test ensures that windows and doors can be operated easily and consistently without excessive effort, supporting both user comfort and accessibility requirements. Operating force limits are defined by performance class and product type and must be met to comply with the NAFS standard.

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The Force to Latch Test:

Measures the amount of force required to fully engage the latching mechanism of a window or door from its open position, simulating the effort a user would apply to securely close and latch the unit. This test ensures that the latching hardware operates smoothly and effectively without requiring excessive force, which is especially important for user safety, security, and accessibility. The force is applied in the direction of normal operation—such as pulling or pushing a sash or rotating a handle—and must fall within limits defined by the product’s performance class to comply with NAFS standards.

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The Air Leakage Resistance Test:

Measures the amount of air that passes through a closed, latched, and properly installed window or door assembly when subjected to a specified static air pressure difference. This test simulates real-world conditions like wind pressure to evaluate how well the product resists unwanted airflow, which can impact energy efficiency, occupant comfort, and building envelope performance. Air infiltration and exfiltration rates are measured in both directions (positive and negative pressure) and must remain within performance class limits defined by NAFS to be considered compliant.

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The Water Penetration Resistance Test:

Evaluates a window or door’s ability to prevent water from leaking through the assembly when exposed to a controlled water spray and a specified positive air pressure differential. Simulating wind-driven rain, this test determines how well the product resists water intrusion under realistic environmental conditions. Water is applied uniformly across the exterior surface while air pressure is simultaneously introduced to mimic storm forces. Any visible water penetration beyond the interior plane of the product constitutes a failure, and performance must meet or exceed the minimum pressure thresholds set by NAFS for the designated performance class.

 

The Uniform Load Deflection Test:

Determines how much a window or door assembly temporarily bends or flexes when subjected to a uniform static air pressure difference, simulating wind load. The purpose of this test is to evaluate the structural behavior of frame and sash components under stress, ensuring they do not deflect excessively in a way that could affect operation, sealing, or long-term performance. Measurements are taken at the midpoint of the largest unsupported spans while pressure is applied and after it is released. To comply with NAFS, the maximum deflection must remain within the allowable limits based on the span length and performance class.

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The Uniform Load Structural Test:

Evaluates the ability of a window or door to withstand extreme wind pressures without experiencing permanent damage or functional failure. A high static air pressure—greater than what is used in the deflection test—is applied uniformly across the product to simulate severe wind events. The test assesses whether components such as frames, sashes, glazing, and hardware can maintain structural integrity without cracking, breaking, disengaging, or becoming inoperable. After the pressure is removed, the unit must show no signs of failure and must still operate as intended to meet NAFS performance requirements for its designated class.

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The product type determines any auxiliary tests that are performed (auxiliary tests are laid out on product specific pages on our website).

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BET currently does NAFS certification for the following products:

• Architectural Terrace Doors

• Awnings, Hoppers and Projected Windows

• Casement Windows

• Fixed Windows

 

With plans to expand in the future!

 

Use our selection tool below to determine which tests are necessary for your product.​

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