Section 26.5.1/Basic Wind Speed
ASCE 7-22 Section 26.5 covers basic wind speed determination from maps based on risk category and geographic location.
The basic wind speed V must be determined from the wind speed maps (Figures 26.5-1A through 26.5-2B) based on the risk category of the building. Risk Category I uses Figure 26.5-2B (lowest speeds). Risk Category II uses Figure 26.5-1A. Risk Categories III and IV use Figure 26.5-1B and 26.5-1C respectively (highest speeds). The wind speed is a 3-second gust speed in miles per hour at 33 feet above ground in Exposure C. For locations between contour lines or near special wind regions, the authority having jurisdiction may require site-specific wind speed studies.
Why this section exists
Wind speed varies significantly by geographic location. Coastal areas experience hurricane winds exceeding 150 mph while inland areas may have design speeds of 95 mph. Higher risk category buildings (hospitals, emergency shelters, essential facilities) use higher wind speeds from different maps because the consequences of failure are more severe. The correct wind speed is the starting point for all wind load calculations. An incorrect wind speed propagates through the entire wind design, either under-designing the structure (unsafe) or over- designing it (wasteful).
What plan reviewers look for
Plan reviewers check the structural general notes for the basic wind speed, risk category, and the ASCE 7 figure reference. They verify the wind speed matches the correct map for the risk category and geographic location. They check that the wind speed is used consistently in the wind load calculations. For projects in hurricane- prone regions, they verify the wind speed accounts for the wind-borne debris region requirements.