Guide To Window DP Ratings

Our guide to window design pressure explores the various aspects behind this important replacement window ratings component. 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 -- with 45 being the divot point between a normal double pane window and a hurricane or impact window. Check out our hurricane impact windows cost calculator to see what these high DR rating windows run in terms of price.

A typical vinyl replacement window will have a design pressure rating between 25 and 35 (DP). Hurricane or 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.

Written By John M. - Site Editor

Basics Behind Design Pressure

DP rating is, in general, an indication of the overall strength of a replacement or new construction window. 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. Homes that are located in hurricane or severe storm prone areas typically require higher DP windows ratings to withstand severe winds and gusts.

Achieving DP Rating

There are a number of steps that manufacturers can take in order to achieve a higher DP window rating. The first, and most important, is to upgrade from a low-e window glass to a laminated glass. Laminated glass is much stronger than low e glass and does not shatter if struck by a hard object (as might happen 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.

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Sample Design Pressure Ratings

Our window design pressure rating chart provides real world dp windows ratings for various replacement window options. As a general rule of thumb, homeowners living in areas that are not 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

Stanek Hurricane Windows » DP70