A “DP” or “design pressure” rating is a numerical value given to a building component that represents its ability to withstand a given amount of wind load. DP ratings represent three performance elements — structural load, water resistance, and air infiltration resistance. A higher DP value indicates a window or door that can withstand more wind, water, and/or structural load than a window with a lower DP.
In practicality, a window or door with a structural DP rating of 50 has passed a structural test pressure of 75 pounds per square foot (equal to a 200 mph wind). A product with a 50 DP rating for water performance has passed testing under conditions of 8” of rain driven at 50 mph, while a 50 DP rating for air performance has withstood air infiltration at 25 mph.
Misrepresentation or partial disclosure of DP testing within the window and door industries has led to a “watering down” of the DP rating. An advertised DP rating had to meet two out of three components of the testing. While some manufacturers advertised the lowest DP rating passed by a product in the interest of full disclosure (thereby demonstrating the high-grade quality of their product), many other manufacturers used the highest value attained in two out the three tests (allowing their product to appear higher in quality).
As a result, to be able to accurately compare one brand’s product to another, the “Performance Grade” or “PG” rating system is being implemented. PG Ratings will be given to products that meet all elements of the testing (the air infiltration, water, and structural loading components) while DP will merely refer to the structural loading aspect. Stop into any of our locations to consult regarding which windows or doors meet the ratings needed for your project.