In wind load terms, which pressure describes the lifting effect on the roof?

• A. Shear pressure
• B. Normal pressure
• C. Uplift pressure
• D. Compressive pressure

Answer: (C)

Uplift pressure is the wind-induced suction that tends to lift the roof surface. When wind flows over a roof, it can create a lower pressure on top of the roof, pulling it upward relative to the building interior. That lifting tendency is what uplift pressure describes.

Other pressures describe different ideas: shear pressure refers to forces acting along the plane of the roof surface (tending to slide components along the surface), normal pressure is the force perpendicular to the surface (which can be either pushing in or pulling away, but doesn’t specifically denote lifting), and compressive pressure is inward pushing toward the roof deck (opposite of lifting). In design practice, uplift pressure is the term used to quantify and specify the lifting effect that roof systems must resist under wind loads.