R, LC, CW, AW. What a window's class really tells you.
The letters on a test report decide which buildings a window belongs in. Here is how to read them.
Vistaza Engineering · Sep 18, 2026 · 6 min read
Windows for commercial buildings in North America are rated to one standard, known as NAFS. The test gives the window two things: a performance class, written as letters, and a performance grade, written as a number. Together they read like CW-PG65.
The letters are the class.
There are four. Each one sets a minimum the window has to reach before it can carry the letters at all.
| Class | Minimum grade | Where it belongs |
|---|---|---|
| R | PG 15 | Houses and small residential buildings. |
| LC | PG 25 | Low-rise and light commercial work. |
| CW | PG 30 | Mid-rise buildings, heavier use, larger sizes. |
| AW | PG 40 | Mid- and high-rise, the hardest test sequence. |
The number is the grade.
The grade is the design pressure, in pounds per square foot, that the tested window withstood. Water resistance is tested at a fraction of that pressure, so a higher grade also means the window was sprayed harder without leaking.
A class without a report number is a claim. Ask for the report.
How to check one.
Ask for the test report number and the size that was tested. The class only applies up to that size. Then look at which type was tested — a fixed window and an operable one from the same series almost never share a rating.
Our classes, with the reports.
| Type | Class | Water |
|---|---|---|
| Vi6 casementIntertek S3614.03-525-44 | AW-PG100 | 15.04 psf |
| Vi6 fixedIntertek S3615.01-525-44 | AW-PG75 | 15.04 psf |
| Vi5 fixedIntertek L4554.02-250-44 | AW-PG70 | 12.11 psf |
| Vi6 hopperIntertek K5829.01-109-44 | CW-PG65 | 12.11 psf |
| Vi6 terrace door, in-swingIntertek J8727.01-109-44 | CW-PG65 | 12.11 psf |