Window Design Pressure
Our guide to window design pressure explores the various aspects behind this important replacement window ratings component. Basically, DP stands for design pressure and is a measure of the amount of simulated wind or pressure can be applied to a window before the structural integrity is compromised. As a rule of thumb, DP rating windows range from 25 to 85.
Typically, a 45 rating is the pivot point between a normal double pane window and an impact window. Check out our hurricane impact windows cost calculator to see what these high DR rating windows run in terms of price.
Written By John M. - Site Editor
Basics Of Window DP Ratings
Generally, window DP ratings are an indication of the overall strength of a replacement or new construction window. So, a DP30 rating means that the window is tested each way for 10 seconds for structual integrity at a maximum speed of 130 miles per hour (which is the top wind speed of a category 3 hurricane). A DP40 rating window means that the unit is tested for 10 seconds for structural integrity at a maximum speed of 155 miles per hour (category 4 hurricane).
A DP50 rating means that the window is tested each way for 10 seconds for structural integrity at a maximum speed of 173 miles per hour (category 5 hurricane). Most residential windows are fine with the DP rating of 30. However, homes that are located in hurricane or severe storm prone areas typically require higher DP windows ratings to withstand severe winds and gusts. The NFRC website is an excellent place to find performance and structural data on thousands of U.S. made windows and patio doors - an excellent resource.
DP Ratings And Overall Performance
Window design pressure is one of the three main tests that determines the overall performance of a window. The other two are air infiltration ratings and water penetration. So, maybe a quick word on these tests (without making it too technical). In terms of air infiltration, scientists subject the windows to 25 miles per hour of simulated wind. They, then measure how how much air passes through the unit.
The window's air infiltration rating does not affect the water or structural tests. However, the window design pressure rating does affect the water and structural testing. Specifically, scientists test water infiltration at 15% of the dp rating and structural at 150% of the dp rating. In practical terms, a DP 30 window keeps out rain from a 42 mile per hour wind, while a DP 40 window keeps out rain from a 49 mile per hour wind.
A typical vinyl replacement window will have a dp rating between 25 and 35 DP. However, hurricane impact windows should have a design pressure of 45 or higher to withstand powerful windows and gusts. A 55 or higher DP window rating is what I like to see in terms of hurricane window design pressure.
Achieving DP Rating
There are a number of steps that manufacturers can take to achieve a higher window design pressure rating. Firstly, and most important, is to upgrade from low-e window glass to laminated glass. Laminated glass is much stronger than low e glass and does not shatter if struck by a hard object. Obviously, the risk of this is high during a hurricane). Instead, the laminated glass may crack, but will remain intact in the frame. In this way, it is similar to an automobile windshield.
Other important upgrades include triple weatherstripping, a strong mainframe for low tolerances, upgraded seals in the insulated glass unit and components that all work to create a stronger and more durable window that can stand up to storms and even hurricane type conditions.
Sample DP Rating Of Windows
Our window design pressure rating chart provides real world dp windows ratings for various replacement window options. Generally, homeowners living in areas that are prone to hurricanes or other large storms should seek out dp rating windows of 55 or higher.
Anderson 400 Series Window » DP30
Marvin Integrity Series » DP40
Vytex Fortis Windows » DP50
Slocomb Windstopper » DP50
Custom Window Systems 8200 Series » DP60
Stanek Hurricane Windows » DP70
Window Design Pressure And Price
John, I am considering three options for hurricane windows for my coastal Maryland home. So, we have 18 windows and 2 patio sliders to replace. The first option is Stanek Windows that have a crazy high design pressure rating that they claim cannot be beat. The total for this option is $56K, which is sorta like, yikes, right?
Second up, there is a local installer who suggested the Wincore 8800 series and that came to $29K all in. Obviously, this is much more within the lines of what we were thinking, but may be these are not good? Finally, Power HRG wants to put in the Northeast Building Products Windforce series. This price point was $34K (obviously I rounded to the nearest thousands on all the cost quotes).
Ideally, we would like a very good impact window with a good DP rating, but also within our price range. Yes, I know this is asking a lot, but what do you think?
Gerry - Homeowner - May, 2025
Website Editor's Answer
Gerry, all three of these hurricane impact windows are quality products, but the Stanek is the best of the bunch. (They are correct that their impact dp window ratings cannot be beat.) However, that price point is prohibitive, and not worth the extra cost for the increased design pressure and overall strength in my opinion. My suggestion is to go with the Wincore 8800 series, which is a quality impact window that is also affordable.
Honestly, I think it checks off all of your boxes. However, window installation is half the equation so you need to make sure that this local installer knows his stuff, has good reviews from past customers, and is gonna do his best on your particular job. If you were to guarantee this, then I think you have a clear winner. The Northeast Building Products would be my backup pick, fyi.
Editor John M. - May, 2025
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