Wind Load Definitions

ASCE7 is the basis for wind load calculation used in most building codes.

International Building Code Model building code developed by the International Code Council. Most of the U.S. has adopted this building code (sometimes with slight, locally adopted variations). The wind load provisions in this code specifically call out ASCE7 to be used in wind load calculations.

Design Pressure The measurement of resistance in both positive and negative directions that an opening must withstand. Design pressures are usually expressed in both positive (PSF+) and negative (PSF-) values. Also known as design load.

Test Pressure The actual tested wind pressure resistance that an opening will withstand during laboratory testing; also known as test load.

Three-Second Gust How wind is measured by the National Weather Service. This data is then compiled into wind maps incorporated into ASCE7 and the International Building Code. The wind speed maps are based on a yearly 2% probability of occurrence (50-year average peak wind).

Mean Roof Height The height above grade level of the midpoint of the roof. Mean roof height is calculated by averaging the eave and ridge heights, and is used as part of design pressure calculations in both ASCE7 and the International Building Code.

Wind Velocity The actual measured speed of airflow during a wind event; usually expressed in MPH. Wind velocity is typically measured at 33 feet (10 meters) above ground level at airports and similar open country locations.

 

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