UNDERSTANDING HURRICANE WINDOW RATINGS
Hurricane impact windows ratings can be a little confusing. At ASP Windows and Doors, we’re experts in supplying and installing the best hurricane impact windows. We provide you with an overview, so you can make an informed decision when buying impact windows.
Let’s begin with the basics of hurricane impact windows ratings. Two terms you might come across when doing your research are Design Pressure (DP) and Performance Grade (PG). The following will describe these terms and their relevance to your safety during hurricane situations.
Some Background on DP Ratings
Design Pressure Rating is a commonly found rating representing the capability of hurricane windows to withstand wind pressure. Impact window ratings are made up of both a positive and negative number representing external and internal pressure. The higher the number on the scale, the better the impact resistance the storm windows offer.
Let’s consider hurricane rated windows or doors with a DP rating of around 50. It should remain intact after application of a test wind pressure of 75 pounds per square foot for 10 seconds.
To get the equivalent wind speed, we then take the square root of this design pressure and multiply that by 20. In this example, a window with design pressure +/- 50 would be able to withstand the equivalent of 142 miles per hour.
A “hurricane proof” windows’ ability to withstand hurricane force winds would depend on the strength of the hurricane. While Florida Building Code requires product approvals for new windows used throughout Florida, south Florida areas like Miami-Dade require impact resistant windows in to be able to withstand particularly high winds because of the catastrophic damage tropical storms inflict in that area.
After the high-speed winds of hurricane Andrew, most properties in Miami-Dade require a design pressure rating of at least +/- 60 to protect against a hurricane of level category 5.
The PG Rating
Another useful evaluation tool is the Performance Grade rating which came into existence to encourage more accurate measurements of efficiency. A product with a PG rating must meet three criteria including water infiltration, air infiltration, and structural load. A hurricane door with a PG rating of 40 may possess two aspects that rate in the 50 range, but the door receives the lowest score of the three.