Why Window, Door & Skylight Performance Ratings Matter

When consumers shop for windows, doors, or skylights, they may think about style first: the color of the frame, the shape of the glass, or how these products will look from outside. The performance of these fenestration products is often an afterthought—something buried in a specification sheet that only contractors, manufacturers, and architects bother to read. Performance ratings determine numerous factors, including how well a house holds up against wind, rain, and time; how much energy bills cost; and how comfortable a home feels. AMMA/WDMA/CSA 101/I.S.2/A440-2026: North American Fenestration Standard/Specification for windows, doors, and skylights is the primary industry standard that establishes and details performance ratings and requirements for windows, doors, and skylights.

Why High-Performance Windows, Doors, & Skylights Matter

High-performing windows, doors, and skylights play a vital role in creating more resilient, sustainable, and comfortable buildings.

Extreme Weather Demands High-Performance Fenestration

Every year, fenestration products—such as windows, doors, and skylights—are exposed to some of the harshest conditions a building can face—from hurricane-force winds, heavy precipitation, freezing temperatures, intense sunlight, and everyday wear. In fact, from 1980-2024, the United States has experienced 403 confirmed weather/climate disaster events with losses exceeding $1 billion. These weather/climate events place unprecedented demands on the building envelope.

Energy Efficiency Starts with High-Performance Windows & Doors

Besides facing harsh weather conditions, windows and doors also influence a building’s energy efficiency. In fact, heat loss through doors and windows can account for up to 30% of a home’s energy consumption; heat loss/gain through windows are responsible for 25%–30% of residential heating and cooling energy use. Furthermore, skylights (or roof windows) provide up to three times more natural light than vertical windows of the same size, significantly reducing daytime electricity use. Window and door performance are therefore critical factors in reducing energy costs and improving sustainability.

Improving Comfort Through Better Fenestration Design

By controlling how heat, cold, light, and sound move through the building envelope, fenestration products dictate a home’s comfort. Essentially, properly designed and selected units eliminate drafts, prevent condensation, and maximize natural light, which drastically improves overall physical and mental well-being.

Key Performance Ratings for Windows, Doors, & Skylights

Windows, doors, and skylights are evaluated against strict, measurable performance criteria to assure energy efficiency, structural integrity, and comfort, such as:

U-Factor – how well a product prevents heat from escaping. Lower numbers mean better insulation.
Solar Heat Gain Coefficient (SHGC) – how much solar radiation passes through the window, door, or skylight. Lower numbers mean less heat gain, which matters especially in hot climates.
Air Leakage (AL) – how much air sneaks through gaps and seals. Lower is tighter and more efficient. AL (or air infiltration) is a critical metric for measuring energy efficiency, as air drafts account for up to 40% of residential heating and cooling energy losses.
Visible Transmittance (VT) – how much natural, visible daylight passes through a window, which affects how bright a room feels without artificial lighting.
Structural and water resistance ratings – how a product holds up under wind pressure and heavy rain, which is especially critical in storm-prone regions.

These performance ratings enable architects, builders, manufacturers, code officials, testing laboratories, and homeowners to objectively evaluate and select windows, doors, and skylights that deliver long-term energy efficiency, durability, weather resistance, and occupant comfort.

What Is AMMA/WDMA/CSA 101/I.S.2/A440-2026?

AMMA/WDMA/CSA 101/I.S.2/A440-2026 is the North American Fenestration standard for windows, doors, and skylights. It is applicable for use in testing and rating windows, doors, secondary storm products (SSPs), tubular daylighting devices (TDDs), roof windows, and unit skylights. The testing provisions of AMMA/WDMA/CSA 101/I.S.2/A440-2026 apply to laboratory testing only.

Intended users of AMMA/WDMA/CSA 101/I.S.2/A440-2026 include building officials, manufacturers, architects, engineers, consumers, builders, contractors, trade associations, test laboratories, specifiers, product evaluation and certification agencies, and government agencies.

The primary purpose of this standard is to enable end-product performance evaluation as may be required for certain US and Canadian model building codes for windows, doors, SSPs, TDDs, roof windows, and unit skylights.

Learn More about AMMA/WDMA/CSA 101/I.S.2/A440-2026

AMMA/WDMA/CSA 101/I.S.2/A440-2022 is jointly published and maintained by the Fenestration and Glazing Industry Alliance (FGIA), a unified organization consisting of the American Architectural Manufacturers Association (AAMA) and Insulating Glass Manufacturers Alliance, the Window & Door Manufacturers Association (WDMA), and the Canadian Standards Association (CSA).

Additionally, you can learn more about AMMA/WDMA/CSA 101/I.S.2/A440-2026 in our blog post: 2026 North American Fenestration Standard.