If you are in the market for new windows or doors in your home you might be hearing the term, Design Pressure or DP Rating, but what does it mean and how should it impact your shopping? This term can sound foreign to most shoppers but it’s very straightforward and can help you select the best windows for your home.
To start, let’s define what Design Pressure Rating means. According to AAMA (American Architectural Manufacturers Association), WDMA (Window and Door Manufacturers Association), and the NAFS (North American Fenestration Standard), a DP Rating is a rating that identifies the load – induced by wind and/or static snow – a product is rated to withstand in its end-use application. Basically, DP Rating measures the strength of a window. It will tell you how well your windows or doors will stand up to high winds or heavy snow. The higher the DP Rating the stronger the window or door.
To calculate a DP Rating, a window or door is attached to a wooden frame and clamped to a specially designed wall. Air pressure is gradually reduced on the inside of the window or door, which increases the pressure on the outside until the window fails or breaks. The test pressure must reach 1.5 times the design pressure for 10 seconds without the window suffering permanent damage. In other words, a window with a DP of 35 would have to withstand 50psf. The instant the window or door fails, the psf is recorded and is used for the calculation. Generally, you’ll see residential replacement windows with ratings from 15 to 50.
The DP Rating needed will vary by location and design of your home. You need to focus on DP Rating if your home is located where weather elements are a particular concern. If you live close to the coast or up high in a structure that is exposed to strong winds we’d suggest going with at least a DP 30. Note, the window doesn’t need to be thick to have a higher rating and a thick window without a higher rating is blocking light for no purpose other than to say it’s ‘better’. A common sales ploy is to show a cutaway view of a thick window next to a thin window and tell them that the thicker window is ‘stronger’ and the thin window is a ‘weak’ window, which is not always the case.
If you have a home on the Texas Coast these are good numbers to keep in mind when building or remodeling.
RED: Indicates an impact window (glass that will not break) along with DP rating up to +60 -60 and on some occasions more.
YELLOW: Indicated a storm window the DP rating up to +50 -50.
BLUE: Indicates a standard none window storm window. These usually have around +35 -30 ratings.
You can always consult your local city or municipality to make sure you are purchasing the correct windows for your project.
Reputable companies will also have no problem helping you verify the DP Rating needed for your windows and doors. Gulf and Basco is Houston’s trusted window dealer and we can assist you with gathering all the information you need to make the best decision. Reach out to us today with any questions you have about your window needs!