Section 30.4.1/Components and Cladding Wind Pressures on Low-Rise Buildings
ASCE 7-22 Section 30.4 provides the simplified method for calculating component and cladding (C&C) wind pressures on enclosed low-rise buildings with mean roof height of 60 feet or less.
Component and cladding (C&C) wind pressures on enclosed low-rise buildings with mean roof height h not exceeding 60 feet are determined using the simplified procedure in Section 30.4. Design pressures are calculated as p = qh x (GCp) - qi x (GCpi), where qh is the velocity pressure at mean roof height, GCp is the external pressure coefficient from Figures 30.4-1 through 30.4-7 based on roof type and zone, GCpi is the internal pressure coefficient, and qi is the velocity pressure for internal pressure. The roof and wall surfaces are divided into interior, edge, and corner zones with increasingly higher pressures at edges and corners due to flow separation. The effective wind area of the component determines which GCp value applies: smaller components experience higher peak pressures. Both positive (inward) and negative (outward/suction) pressures must be checked. The basic wind speed and exposure category determine qh.
Why this section exists
C&C pressures govern the design of roofing, wall cladding, windows, doors, and their attachments to the building structure. These pressures are higher than the main wind-force resisting system (MWFRS) pressures because individual components experience localized peak pressures from turbulent eddies, vortices, and flow separation at corners and edges. The zone system (interior, edge, corner) reflects the aerodynamic reality that pressures near roof edges and wall corners can be two to three times the pressures at interior zones. Roof membrane blow-off, window failures, and loss of wall cladding are the most common types of wind damage to buildings, all driven by C&C pressures rather than MWFRS pressures.
What plan reviewers look for
Plan reviewers check the structural calculations for C&C pressure calculations at roof edges, corners, and interior zones. They verify the correct zone widths are used (typically 10% of the least horizontal dimension or 0.4h, whichever is smaller, but not less than 4% of the least horizontal dimension or 3 feet). They check that the effective wind area matches the component being designed (a single roof shingle vs. a large metal panel). They verify both positive and negative pressures are checked. For fenestration, they verify design pressure ratings of windows and doors meet or exceed the calculated C&C pressures for their zone location.