A design pressure (DP) rating is the wind load, in pounds per square foot, a window or door is tested to withstand, both pushing in and pulling out. Higher numbers mean the opening can handle stronger wind pressure. In the HVHZ, each opening must meet the pressure calculated for its exact location on your home.
Reading a DP rating
See also:Impact windows →Ratings are usually written as two numbers, such as +60 / −70. The first is positive pressure (wind pushing in); the second is negative pressure (suction pulling out). The negative number is often the one that governs.
Why openings on the same house need different ratings
- Corners: wind accelerates around the edges of a building
- Upper floors: wind speed increases with height
- Large openings: more glass area, more total load
- Exposure: open water or open land nearby raises pressures
How pressures are calculated
An engineer calculates the required pressure for each opening from your home’s height, roof shape, exposure and location in the wall. The window you buy must meet or exceed that number at its size. We include the calculations with the permit package.
DP rating vs. impact rating
Impact rating tells you the glass and frame survived a debris impact test. Design pressure tells you how much sustained wind pressure the unit handles. In the HVHZ, a window needs both: the impact rating to resist flying debris and a DP rating that meets the calculated pressure for its location.
Where higher ratings usually show up
| Location | Why |
|---|---|
| Within a few feet of a building corner | Wind accelerates at edges |
| Second floor and above | Higher wind speeds with height |
| Wide sliders and picture windows | Large area means large total load |
| Homes near open water or open land | Less shielding from surrounding buildings |
Can a higher DP be a waste of money?
Sometimes. Buying every window at the highest rating can add cost without adding real protection where pressures are lower. Matching each opening to its calculated requirement, with sensible margin, is usually the better value.
What to look for on your quote
- A DP rating listed per opening
- Ratings that meet or exceed the engineering calculations
- The approval number that supports each rating
Frequently asked questions
What does DP 50 mean?
The unit was tested to withstand 50 pounds per square foot of design wind pressure.
Do sliding doors need higher DP ratings?
Large sliders often need careful selection because their size increases total load.
Who decides the DP my windows need?
An engineer calculates the required pressures for each opening based on your home.
Is a higher DP always better?
Higher is stronger, but the right choice meets the requirement without overspending.
About the author
Roshy Rajan has worked in Broward County real estate and construction since 2006. He founded SafeTech Roofing and Windows (SafeTech Builders Inc.) after a hurricane left a friend with roof and window damage and the referrals kept coming. Florida Certified General Contractor CGC1537934 · Certified Roofing Contractor CCC1336954 · BBB Accredited.
