What Do Design Pressure (DP) Ratings Mean?

What is a Design Pressure Rating for Windows?

‍Let’s start with the definition of Design Pressure. According to AAMA (American Architectural Manufacturers Association), WDMA (Window and Door Manufacturers Association), and the NAFS (North American Fenestration Standard), Design Pressure (DP) 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.

So basically, DP is a performance specification for how strong a window is, expressed in how many pounds per square foot (psf) of pressure the window can withstand. This specification can fluctuate based on several factors, such as:

• Geographic location
• The height of the building
• The location of the window in relationship to the building
• And more

All of these factors are used to calculate what the Design Pressure (DP) is for a specific window or door.

Key Florida DP Rating Information:

• Coastal Regions: Areas prone to higher wind speeds, such as Miami-Dade and Broward counties, require higher DP ratings (often DP 50-60+) to withstand hurricanes.
• Inland Regions: Central Florida locations may require lower ratings, such as DP 35, due to reduced wind exposure.
• Code Requirements: The "25% rule" applies: if you replace 25% or more of your home's windows, the new ones must meet current, site-specific building code DP and impact-resistance requirements.
• What it Measures: A DP rating (e.g., DP 50) indicates the product can handle 150% of its rated pressure (e.g., 75 pounds per square foot)

Window Design Pressure Rating Process

During testing, we attach a window or door to a wooden frame and clamp it to a specially designed wall. Testers gradually reduce the air pressure on the inside of the window, which increases the pressure on the outside until the window fails (breaks beyond repair).

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 30 would have to withstand 45 psf.

The instant the window fails, the tester records the psf to use for the calculation. Laboratories will then issue labels that indicate the DP for the window or door. The Window and Door Manufacturers Association (WDMA), the American Architectural Manufacturers Association (AAMA) and other organizations use these labels.

What Window DP Rating Do You Need?

In Florida, the required window Design Pressure (DP) rating is determined by the Florida Building Code based on wind zone, building height, and location (coastal vs. inland), typically ranging from DP 35 in central Florida to DP 60-70+ in coastal areas and HVHZ (Miami-Dade/Broward). Minimums for impact protection are generally DP 50, with high-velocity zones requiring DP 70 to 100+

Your local building department can assist you in determining what DP rating you need, based on the location and design of your home. Most municipalities have maps or easy-to-read charts that clearly explain the requirements you will need to meet in order to effectively protect your home with the proper Design Pressure.

You can then verify that the windows you are considering meets the required DP rating by checking the sticker on the window and matching it to the engineering drawings for that window.

Important Notes:

• The 25% Rule: If you replace 25% or less of your total window area in 12 months, the new windows may not need to meet current impact-resistant codes, depending on local jurisdiction enforcement of FBC-EB Section 706.4.
• Check Local Code: Always verify specific requirements with your local building department, as regional requirements vary significantly