The primary environmental factor used to define wind exposure categories is:

• A. Terrain openness
• B. Roof slope
• C. Insulation type
• D. Color of roofing material

Answer: (A)

Wind uplift on a roof is driven largely by how open or shielded the surrounding area is. The factor used to define wind exposure categories is terrain openness because it directly reflects how much wind is slowed or redirected by nearby features like buildings, trees, and hills. In open terrain, there are few obstructions, so winds stay strong near the roof and uplift pressures are higher. In urban or wooded settings, obstructions provide shielding, reducing wind speeds and peak pressures. So, the exposure category is determined by how open the terrain is. The other options don’t set exposure categories: roof slope doesn’t define exposure level, and insulation type or color of roofing material don’t influence wind uplift pressures.