ASCE 7-22 Chapter 30 | Components & Cladding (C&C) Wind Pressures
Individual roof panels, windows, mullions, and purlins do not feel the smoothed average wind load of the whole building. Localized wind vortices curling around roof corners generate intense suction pressures that strip panels off buildings.
Governing Formula
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Notation & Variables
Worked Example
Calculate velocity pressure qh
For a 30-foot building in Exposure C with V = 115 mph: qh = 24.4 psf.
Find zone pressure coefficient
For a roof corner (Zone 3) with small effective wind area (10 sq ft): GCp = -2.8.
Compute net suction pressure
Include positive internal pressure: p = 24.4 * (-2.8 - 0.18) = -72.7 psf uplift.
When does this govern?
Governs roof fastener pullout, window and curtain wall glass thickness, and roof perimeter decking attachment.
Common Mistake
Using Main Wind Force Resisting System (MWFRS) wind pressures to design roof purlins or wall studs. C&C pressures are frequently 200% to 300% higher than MWFRS pressures!