All About Design Pressure Ratings of Windows
If you’re replacing the windows in your home, you’re going to look at a variety of factors including price, ease of installation and aesthetic appeal. But something you want to take note of is a window
All About Design Pressure Ratings of Windows
If you’re replacing the windows in your home, you’re going to look at a variety of factors including price, ease of installation and aesthetic appeal. But something you want to take note of is a window’s design pressure rating.
Before you had to replace your windows, you may have never heard of design pressure. In fact, that might be why you’re reading this article. You heard that your windows need to meet your location’s DP requirements, and you want to fully understand what that means before you proceed.
Defining Design Pressure
DP stands for design pressure. As defined by the AAMA (American Architectural Manufacturers Association), WDMA (Window and Door Manufacturers Association), and the NFRC (National Fenestration Rating Council), design pressure is a rating that identifies the load – induced by wind and/or static snow – that a product is rated to withstand in its end-use application. What this means is that a lab has carefully tested a window’s design pressure by measuring how many pounds of pressure per square foot a window can take.
When the required DP of your home is being calculated, a number of things are taken into consideration, including geographic location, the height of the building and the location of that window in the building. A home in Florida, for example, may have a design pressure requirement of 35 in the center of the state, but a DP of 60 along the coast. With winds and potential hurricanes, the geographic location of the coastal homes requires a stronger DP.
Now knowing what DP stands for, and what it entails, you’re likely feeling more strongly about it. You no longer just want to find out what it means, now you’re committed to getting the proper windows installed, especially if you live in a weather risk area. Before we talk about how to find out about your area’s design pressure requirements, let’s learn about what determines it, and how carefully it’s tested.
You’ll be interested to know that when a window’s design pressure is determined, it isn’t an arbitrary estimate. No one at a desk does some quick calculations based on glass thickness and window size, then stamps an estimated DP onto the window design. No, a true design pressure test is like something right out of MythBusters–including a huge shattering of glass.
When a lab is testing for design pressure, they hook the window up to a special test. The window is attached to a wooden frame, which is then clamped to a specially designed wall. The air pressure inside of the window is then reduced, increasing the outside pressure, until the window breaks. A careful record is made of how long the window lasts, under what pressure.
To determine a tested window’s design pressure rating, the test pressure must reach 1.5 times the design pressure for 10 seconds without the window suffering permanent damage. In other words, a 30 DP window would have to withstand 45 pounds of pressure per square foot. So, any window in your house that has a design pressure rating of 30 can withstand 10 seconds of 45 pounds per square foot of pressure. That’s pretty good!
After the testing process is complete, labs then issue labels that indicate the DP of that window. These labels are used by the WDMA, AAMA and others. You can rest assured knowing that the DP on the label is trustworthy. It’s not a rough estimate–it’s been lab tested, and pretty dramatically at that!
Incorporating Design Pressure
Now that you know what DP is, and how it’s determined, you’re ready to find out what your windows need to be. A quick hike to the store will tell you what windows are available for you to buy, but it won’t tell you what your required DP is.
It’s not something you want to estimate, either. Failure to meet DP requirements could result in a catastrophe. Seal-damaged windows create flooding problems, and a window too weak to withstand a mild storm could be the difference between a house saved and a house lost. Whatever your location and weather, you’ll want to meet you area’s DP.
Easier said than done, right? Just exactly where do you start? National building codes now require window testing, and your location will have a required window design pressure rating. Your needs will vary based on your type of home, its size, and your location. Most municipalities have maps or easy to read charts that explain the requiremen