Section 28.4.1/Wind Loads on Low-Rise Buildings (Envelope Procedure)
ASCE 7-22 Section 28.4 covers the envelope procedure for MWFRS wind pressures on low-rise buildings with mean roof height 60 feet or less.
The envelope procedure (Chapter 28) provides a simplified method for determining MWFRS wind pressures on enclosed and partially enclosed low-rise buildings with a mean roof height of 60 feet or less. Wind pressures are determined from Figure 28.4-1 using the external pressure coefficients (GCpf) for each building surface zone. The design pressure is p = qh[(GCpf) - (GCpi)], where qh is the velocity pressure at mean roof height and GCpi is the internal pressure coefficient. The envelope procedure accounts for the critical loading patterns that produce the maximum structural effects by combining different pressure zones.
Why this section exists
Most buildings in the United States are low-rise (60 feet or less). The envelope procedure provides a straightforward method for these common buildings without the complexity of the directional procedure (Chapter 27), which requires evaluating pressures for multiple wind directions. The envelope procedure uses a set of critical load cases derived from wind tunnel testing that capture the worst-case structural effects regardless of wind direction. For most low-rise buildings, this produces design pressures equivalent to or slightly more conservative than the directional procedure.
What plan reviewers look for
Plan reviewers check the structural general notes for the wind design method (envelope or directional). For the envelope procedure, they verify the mean roof height is 60 feet or less. They check the velocity pressure qh calculation using the correct wind speed, exposure category, and topographic factor. They verify the GCpf values from Figure 28.4-1 for the correct roof slope and building geometry.