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An exposure category shall be determined in accordance with the following:
Exposure B. For buildings with a mean roof height of less than or equal to 30 feet (9144 mm), Exposure B shall apply where the ground surface roughness, as defined by Surface Roughness B, prevails in the upwind direction for a distance of not less than 1,500 feet (457 m). For buildings with a mean roof height greater than 30 feet (9144 mm), Exposure B shall apply where Surface Roughness B prevails in the upwind direction for a distance of not less than 2,600 feet (792 m) or 20 times the height of the building, whichever is greater.
Exposure C. Exposure C shall apply for all cases where Exposure B or D does not apply.
Exposure D. Exposure D shall apply where the ground surface roughness, as defined by Surface Roughness D, prevails in the upwind direction for a distance of not less than 5,000 feet (1524 m) or 20 times the height of the building, whichever is greater. Exposure D shall apply where the ground surface roughness immediately upwind of the site is B or C, and the site is within a distance of 600 feet (183 m) or 20 times the building height, whichever is greater, from an Exposure D condition as defined in the previous sentence.

Related Code Sections

1609.4 Structural Design, Exposure Category
For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall ...
1609.4 Structural Design, Exposure Category
For each wind direction considered, an exposure category that adequately reflects the characteristics of ground surface irregularities shall ...
1609.4.1 Structural Design, Wind Directions and Sectors
For each selected wind direction at which the wind loads are to be evaluated, the exposure of the building or structure shall be determined ...