Window DP Rating and Performance Grade Explained

A window's DP (design pressure) rating is the wind load, in pounds per square foot, that the window was tested to carry, pushing in and pulling out ^{3 7}. The performance grade, or PG, is the newer and fuller rating: it means the window passed that structural test and also the air leakage, water penetration and other tests of the North American Fenestration Standard, AAMA/WDMA/CSA 101/I.S.2/A440 ^{1 4}. A label reading R-PG50, for example, describes a residential-class window that met the standard's requirements at a design pressure of 50 pounds per square foot ^{1 3}.

A higher grade matters where the wind load on the wall is higher: higher design wind speeds, open exposure such as a waterfront, taller walls and windows near the edges of a wall ^{3 5 6 7}. Your building department sets the minimum, not the manufacturer ³.

DP rating vs. performance grade

Andersen explains the change: performance grade replaced design pressure as the preferred rating, and a DP rating now describes a product tested only for structural loading, not for air infiltration and the other requirements ⁴. FGIA says the standard drew this line in its 2008 edition because some manufacturers were marketing products on their DP rating alone ¹.

So a window sold as "DP50" and one labeled "PG50" are not the same claim. The first was tested for structure; the second for structure, air and water at that grade ^{1 4}. When a quote lists only a DP, ask whether the unit has a PG and at what size.

How to read the label

The NAFS rating has a primary designator: the performance class, the performance grade and the size tested ². Secondary designators can add the positive and negative design pressures, the water test pressure and the air leakage level ².

• Class. NAFS has four classes, R, LC, CW and AW, and FGIA says the class is chosen independently of the building's use ¹. A quick reference guide hosted by FGIA, written for the 2008 edition of the standard by a Canadian industry group, gives the minimum grade for each class as 15 psf for R, 25 for LC, 30 for CW and 40 for AW ².
• Grade. A single number that represents structural and water performance, such as PG25 or PG30 ². FGIA defines it as a set of performance requirements matching a design pressure range ¹.
• Size tested. The size tested is part of the rating's primary designator ². Ask whether the size you are buying is covered by the listed rating.
• Positive and negative. Wind can push on a window or pull on it, and a DP rating covers both directions ⁷.

Joined units are a special case. Andersen says a single unit can be tested and given a PG, but a mulled (joined) assembly whose joining hardware was calculated rather than tested gets only a design pressure, based on the load the joining material is engineered to carry ³.

What the tests behind a grade involve

The grade ties several tests to one number. In Andersen's summary, a PG requires an air leakage test at 1.57 psf, a water test of four cycles, each with five minutes under pressure and one minute without while the spray continues, and two uniform-load tests in both directions under ASTM E330 ⁴. The structural test is run at 150 percent of the design pressure for windows and doors, according to FGIA ¹.

The water test pressure rises with the grade. FGIA says residential products are tested at 15 percent of the design pressure, with a minimum of 2.90 psf, and that the water test pressure is capped at 12 psf in the U.S. ¹. On those rules, our arithmetic gives a PG50 window a water test at 7.5 psf and a structural test at 75 psf, while a PG30 window is water-tested at 4.5 psf. That is why a higher grade says something about wind-driven rain as well as wind.

The vinyl windows buying guide covers the separate AAMA Gold Label listing and reinforcement that can lift a vinyl window's grade.

How the required grade is set

Building codes set the wind load a window must resist, not a brand. Charleston County's window permit form quotes the 2021 International Residential Code: R609.2 says exterior windows and doors shall resist the design wind loads in Table R301.2.1(1), adjusted for height and exposure, and R609.3 says exterior windows and sliding doors shall be tested by an approved outside laboratory and labeled to show compliance with AAMA/WDMA/CSA 101/I.S.2/A440 (Charleston County window and door form) ⁵. The county asks for the design pressure rating of the windows with every window or skylight replacement submittal ⁵. Each jurisdiction adopts and amends its own edition, so the local version governs.

The inputs are wind speed, exposure, height and position on the wall. Jacksonville, Florida, which builds under the Florida Building Code rather than the IRC, shows how they come together in its Window and Door Replacement Worksheet (Jacksonville window and door worksheet) ⁶:

• Wind speed. For Risk Category II structures, the city sets 125 mph west of its demarcation line and 130 mph east of it ⁶.
• Exposure. Category B is protected by woods or structures for at least 1,500 feet, D is exposed to open terrain or water for 5,000 feet (with a further case within 600 feet of the water's edge), and C is everything else ⁶.
• Wall zone. The worksheet asks for each window's rated pressure for the end zone and the interior zone of the wall ⁶. FLASH explains why: pressure is greater near the edges of a wall, so a window there may need a higher rating than one in the middle ⁷.

Andersen adds that it is not authorized to decide code compliance and that only local building code officials can approve a product as meeting code ³.

When a higher grade matters

• Coastal and open sites. Exposure is one of the inputs to a building's design pressure ³, and Jacksonville's category D covers sites exposed to open terrain or water ⁶. Andersen says most of its 400 Series windows are PG 50 and most A-Series products meet PG 70, upgradable to PG 70+, on its coastal windows page ⁹. More on salt, finishes and flashing is in windows for coastal homes.
• Corners and edges. Windows near the edge of a wall see higher pressure than mid-wall windows ⁷.
• Large units and tall walls. Height adjusts the load in R609.2 ⁵, and the rating holds for the size tested.
• Shutters do not lower it. FEMA advises designing the window to resist the full design loads even where shutters protect it ⁸.

A grade is not an impact rating. FLASH notes that DP reflects wind pressure only, not impact from windborne debris ⁷; where debris protection applies, see hurricane impact window cost. Nor does a grade say anything about energy use, which is on the NFRC label explained in energy-efficient windows explained.

The aim is to meet or exceed what each wall needs, which is a question for the building department rather than the highest number on offer. Comparing grades across brands is covered in replacement windows compared.

Questions for each quote

1. What is the performance class and grade of each window at the size quoted, and where is it listed?
2. Is any figure given only as a DP rating, and why?
3. What design pressure does my building department require for each wall zone at this address?
4. Are any units mulled, and what design pressure do the joints carry?

How to compare window quotes has a line for each of these. When you are ready, you can compare quotes from window installers.

We are not affiliated with the manufacturers named.

About these figures

• ¹ Official record + Estimate: FGIA performance class overview (R, LC, CW and AW classes, PG definition, the 2008 change, 15 percent water test pressure with a 2.90 psf minimum and a 12 psf cap in the U.S., structural test at 150 percent); the 7.5, 75 and 4.5 psf figures are our arithmetic from those rules, checked October 27, 2026.
• ² Reported: NAFS quick reference guide by FEN-BC hosted by FGIA (primary designator including size tested, secondary designators, class minimums of 15, 25, 30 and 40 psf), February 2014, written for the 2008 edition, checked October 27, 2026.
• ³ Reported: Andersen design pressure FAQ (definition in psf, inputs to a building's design pressure, PG50 example, mulled units, local code officials), checked October 27, 2026.
• ⁴ Reported: Andersen help article on performance grade versus design pressure and the tests behind a PG (1.57 psf air test, four water test cycles, ASTM E330 load tests), checked October 27, 2026.
• ⁵ Official record: Charleston County window and door form quoting 2021 IRC R609.2 and R609.3, checked October 27, 2026.
• ⁶ Official record: City of Jacksonville Window and Door Replacement Worksheet, revised April 3, 2026 (125 and 130 mph wind speeds for Risk Category II, exposure categories at 1,500 and 5,000 feet, end zone and interior zone pressures), checked October 27, 2026.
• ⁷ Reported: FLASH article on design pressure ratings (pushing and pulling, higher pressure near wall edges, DP is not an impact rating), January 23, 2026, checked October 27, 2026.
• ⁸ Official record: FEMA P-499 Fact Sheet 6.2 advice to design glazing for full design loads where shutters are used, 2010 edition, checked October 27, 2026.
• ⁹ Reported: Andersen coastal windows page on PG 50 for most 400 Series windows and PG 70 for most A-Series products, checked October 27, 2026.