Impact windows have both a grading system and a rating system. Both grades work towards letting you know how efficient that window is going to be for your needs. However, one system is more reliable than the other.

Here’s Why.

DP Rating
The DP rating stands for Design Pressure Rating. This rating measures:

  1. Water Resistance.
  2. Air Infiltration Resistance.
  3. Structural Load.

Impact windows are tested to see how much pressure they can take before breaking. These measurements are not taken by any computer that has been provided with manufactures specifications. Tests are done in realistic conditions. For example, consider a window that has a DP rating of 35. In order for it to get that rating it must first withstand a pressure of 52.5 PSF for 10 seconds.

The DP rating takes the highest two scores to provide the final rating.

This can be a Problem.

If you get an impact window with a DP of 40, you may expect it to withstand a category 4 hurricane. But as it is only based on the highest 2 scores it may not be as good as you expect.

For instance, if it scored low on water resistance and the hurricane brings a lot of sideways sweeping rain, this could weaken your window and lead to damage.

It is important to check the PG rating or other rating information that comes with that impact window.

PG Grades
The PG Grading system stands for Performance Grade Rating.

This is tested for the same things as the DP rating. That is Water Resistance, Air Infiltration Resistance, and Structural Load.

Testing is also similar to how one would get the results for a DP rating. The difference between PG Grades and DP ratings is how the results are calculated. PG Grading is a newer way of calculating the grade, it is also a safer way.

With a PG rating, the grade is based on the result of all three tests. If even one of those tests gives a low score, the rating drops to reflect that score. Therefore, a window with a PG rating of 40 will withstand a Category 4 hurricane.

Impact Grades Made Easy
The easiest way to know how good a grade your impact window has is to remember the following format.

  • PG 10 Category 1 Hurricane. (74-95mph)
  • PG 20 Category 2 Hurricane. (96-110mph)
  • PG 30 Category 3 Hurricane. (111-129mph)
  • PG 40 Category 4 Hurricane. (130-156mph)
  • PG 50 Category 5 Hurricane. (157+mph)

Bottom Line
Yes. There are grades to help you find the right impact rating window for your area. Keep in mind that the newer PG grades are more reliable than the older DP ratings. Also, remember that the grade you need is dependent on where you live. Check with your local council or impact window supplier if you are unsure.

Are you looking at installing impact windows and doors in your home? If so, we can help. Contact G&R Impact Windows and Doors by calling us for expert advice and assistance on getting the right impact windows and doors for your home.