Wind exposure

We all intuitively know that the wind affects things on the ground. But did you know that things on the ground also affect the wind? Highly developed environments tend to slow down the wind but increase gustiness, while open terrain lets wind flow faster, but with fewer gusts.

The American Society of Civil Engineers (ASCE) publication Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10) forms the basis for most building codes in the United States. ASCE/SEI 7-10 specifies several upwind exposure categories:

  • Exposure category B: Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger.

  • Exposure category C: Open terrain with scattered obstructions having heights generally less than 30 ft. (9.1 m); this category includes flat open country and grasslands.

  • Exposure category D: Flat unobstructed areas and water surfaces; this category includes smooth mud flats, salt flats, and unbroken ice.

There was once an Exposure category A, which corresponded to highly built-up areas like urban centers, but this category has been superseded by more sophisticated wind tunnel methods.

Depending upon the terrain and built environment in which a structure is sited, the upwind exposure may vary with wind direction. A warehouse located on the western fringes of a suburb may have an Exposure B approach for winds from the east and an Exposure C approach for winds from the west.

When we conduct a wind tunnel study at CPP, we account for upwind exposure in 10-degree increments. Our clients benefit from such a fine-tuned approach with material and labor cost savings and improved reliability.

CPP understands the unique challenges that your project faces. Rely on our experienced wind engineers to deliver the information you need to make your next project safe, comfortable, and efficient. Please contact CPP today to discuss your specific needs with a member of our team.