Design pressure rating
Also called: DP rating, design pressure, DP50, wind load rating, performance grade, PG rating
The wind load a window or door is tested to withstand, in pounds per square foot, given as positive and negative values (for example +50/−60). The code sets the DP an opening needs from wind speed, exposure, height and position; the product must be rated at or above it.
Wind doesn’t just push on a window; it pulls. As a hurricane passes, pressure on the windward side pushes the glass in, and suction on the leeward and corner walls pulls it out — the negative number, which is usually the larger one and the one that fails first. A design-pressure rating certifies that the assembled window (frame, sash, glass, hardware, anchors) held a test pressure of 1.5 times the DP without failure, plus water and air infiltration tests at lower pressures.
What your opening needs is calculated, not guessed: from the design wind speed on the code’s map (130–180 mph across coastal Florida and the Gulf), the exposure category (open coast versus suburban), the building’s height and roof shape, and where on the wall the opening sits — corners and upper floors see the highest suction. A one-story inland house might need DP 35; a corner window on a two-story house near the beach in the High-Velocity Hurricane Zone might need DP 70 or more. The building department, the installer or an engineer’s letter supplies the number, and the permit review checks it.
The DP appears on the window’s product approval and its label, by size — the same series carries a lower rating at larger sizes. Impact resistance is a separate test; a window can be impact-rated at one DP and not at a higher one. A quote that lists the product but not the DP, or a DP below the opening’s requirement, is a quote that won’t pass inspection.