The Basics of Impact Window Ratings

Many homes in South Florida are equipped with impact windows to protect them from flying debris during a hurricane or strong tropical storm. If you’ve considered buying impact-resistant windows for your home, you’ll be able to make a well-informed decision by understanding some of the terms that apply to these products. There are two terms that you often here when inquiring about or researching different brands and comparing price points – “DP” or design pressure and “PG” or performance grade.

DP Ratings

The design pressure rating represents an impact windows’ ability to withstand the force of high wind pressure. The numerical rating encompasses 3 different criteria:

  • Air infiltration
  • Structural load
  • Water infiltration

The higher the rating, the better it can withstand these criteria. For instance, consider impact windows with a 50 DP rating. This means that the window can withstand 75 pounds of pressure per square foot. However, there have been cases where the manufacturer, either deliberately or inadvertently, misrepresented the rating. Most fabricators or manufacturers are accurate and honest when listing a DP rating. However, there are some who misrepresent the efficacy (effectiveness) of their window products by using a higher rating number.

PG Ratings

Performance grade ratings were developed out of a need to encourage or promote more exact measurements of an impact-resistant windows’ efficiency and are a newer, updated type of rating system. Unlike the DP rating that only has to meet 2 of the 3 aforementioned criteria, PG ratings must meet all 3 – NO EXCEPTIONS!  For example, impact windows with a rating of 40 may score in the 50 range on two of the criteria but will receive a lower score overall.

How to read the Ratings

Hurricane categorization is calculated according to the Saffir-Simpson Hurricane Wind Scale. By simplifying the numbers, the category scale looks like this:

  • Category 1:  74-95 mph
  • Category 2:  96-110 mph
  • Category 3:  111-129 mph
  • Category 4:  130-156 mph
  • Category 5:  157+ mph

If we convert the categories of the scale above into 10-point levels (10, 20, 30, . . . . . ) on the DP rating, a DP rating of 50 would mean that the impact-resistant glass could withstand hurricane-force winds of 157 mph or higher (technically, impact windows are supposed to hold up to winds much stronger than that).  Keep in mind that DP ratings do not take accompanying tornadoes, projectiles, or strong wind gusts into account. They only apply to sustained winds.

That is why it is important to buy quality impact windows and doors by V & V Windows. They are U.S.-based manufacturers that offer a wide range to keep your home and business safe. By directly selling their products, you get to enjoy considerable discounts and affordable prices. Visit their showroom to see the impact doors and windows before you buy.