Wind Load Calculator for Windows and Doors

Zone 4 and Zone 5: why corners matter

Wind accelerates around the corners of a house and pulls hardest on the walls there. ASCE 7 divides each wall into Zone 5, a strip at each outside corner, and Zone 4, everything else. For a small window, Zone 5 suction is about 23% higher than Zone 4.

The corner strip is 10% of the house's shortest side or 40% of the mean roof height, whichever is smaller, but never less than 3 ft. A 60 × 40 ft one-story house has a 4 ft strip. If any part of a window's frame falls inside the strip, the whole window uses Zone 5.

Exposure C or D

Exposure describes the ground the wind crosses before it reaches your house. Most South Florida neighborhoods use Exposure C. Homes on a shoreline facing open water, such as Biscayne Bay, the ocean or a large lake, can fall under Exposure D, where wind arrives faster because nothing slows it down. Exposure D raises design pressures by roughly 20%. The engineer who seals your calculation makes the final call. For the ASCE 7 definitions of B, C and D and how terrain feeds velocity pressure, see the wind exposure category guide.

Design pressure is the strength side of the spec. In the wind-borne debris region, glazed openings also need impact protection: impact-resistant windows and doors, or an approved shutter system. Miami-Dade, Broward, and Palm Beach are inside that region for a typical home. The region is a separate code question from exposure and from the pressures this calculator estimates. To see how a product's design pressure, missile impact rating, and HVHZ approval appear together, read hurricane window ratings explained. The calculator assumes a Risk Category II home; schools, assembly buildings and essential facilities use higher wind speeds, as the building risk category guide explains.

Why the pane size matters

Smaller pieces of glass see higher peak pressures, because short gusts can load a small area all at once. Miami-Dade's chart sets the effective wind area of a window as one pane of glass, and of a sliding glass door or French door as one leaf. A 37 × 63 in single-hung window counts as one 37 × 31.5 in sash, about 8 sq ft. A sectional garage door uses one panel, about 24 in tall, across the full width. The calculator applies these rules for you.

What to do with your numbers

1. Use the results to shop. A product fits an opening only if its positive rating and its negative rating both meet or exceed that opening's numbers, for the size you need. The rating is listed on the product's Miami-Dade NOA or Florida product approval. Our design pressure guide explains how to read them.
2. Check the approval. The Miami-Dade product control search and the Florida product approval search show each product's ratings and size limits. In the HVHZ, the approval must be valid for HVHZ use.
3. Get the calculation sealed. Your contractor submits wind load calculations with the permit, sealed by a Florida PE unless your building department accepts a county chart for your home. See the Florida Building Code guide for the permit process.