What is the role of exposure category in wind load design per ASCE 7?

• A. Controls the maximum allowable building height.
• B. Specifies the color of exterior finishes.
• C. Defines the surrounding terrain roughness affecting wind pressure.
• D. Has no effect on wind design.

Answer: (C)

Exposure category captures how rough the surrounding terrain and obstacles are around the site, and that information directly influences the wind pressure used in design. In ASCE 7, the wind pressure a structure must resist depends on the velocity profile with height, which is shaped by terrain roughness and obstructions. A more open terrain allows winds to accelerate more with height, leading to higher pressures at the building height, while denser urban or suburban surroundings dampen and distort the wind flow. Therefore, selecting the appropriate exposure category adjusts the calculated pressure values that govern the wind design. It’s not about building height or exterior color, and it does affect the wind loads used in the design.