Wind Loads (ASCE 7-22)

How it calculates

The Wind Loads (ASCE 7-22) calculator determines design wind pressures for low-rise buildings in the US per ASCE 7-22. Each sheet runs one of three procedures: Components and Cladding (C&C) per Chapter 30, the MWFRS Envelope Procedure per Chapter 28, or the MWFRS Directional Procedure per Chapter 27.

Site and building inputs

Key inputs are:

• Basic wind speed (V) - taken from the project defaults, or entered directly when you override them
• Exposure category - B, C, or D, which sets the velocity pressure exposure coefficient K_h
• Building dimensions - mean roof height (h), least horizontal dimension (B_min), and roof slope
• Roof type - flat, gable, hip, or monoslope for C&C; gable or flat for the Envelope Procedure
• Enclosure classification - enclosed, partially enclosed, partially open, or open, which sets the internal pressure coefficient (GCpi). Open is not offered for the Envelope Procedure or for flat and hip roofs.
• Topographic factor (K_zt) - computed from hill height, half-length, and site distance per ASCE 7-22 Cl. 26.8, or 1.0 where no hill or escarpment is present
• Ground elevation factor (K_e) - based on elevation above sea level per ASCE 7-22 Cl. 26.9, either looked up from the project address or entered

The wind directionality factor K_d is fixed at 0.85.

Velocity pressure

Velocity pressure at mean roof height is:

q_h = 0.00256 × K_h × K_zt × K_e × V² (lb/ft², V in mph)

K_d is not part of q_h. It is applied in each design pressure equation instead. For the Directional Procedure, velocity pressure q_z is also tabulated by height up the windward wall.

C&C pressures (ASCE 7-22 Ch. 30)

External pressure coefficients (GCp) are looked up as a function of effective wind area and zone. Roof zones are 1, 2 and 3. Flat and low-slope roofs add zone 1', and some low-slope monoslope roofs add zones 2' and 3'. Walls use zones 4 and 5. Net design pressure combines external and internal coefficients:

p = q_h × K_d × [(GCp) ± (GCpi)], not less than 16 psf in magnitude

Zone width a is calculated automatically from building dimensions, along with 0.6h and 0.2h for flat and low-slope roofs. Pressures are reported for the roof and wall effective areas entered, or for individual effective areas per zone. Roof overhangs, parapets and attached canopies can be added. Open buildings with gable or monoslope free roofs use net pressure coefficients instead of GCp and GCpi.

MWFRS pressures

For the Envelope Procedure (Chapter 28), wall and roof zone pressures are reported for two load cases. Load Case A has wind perpendicular to the ridge, and Load Case B parallel to it. For the Directional Procedure (Chapter 27), wall and roof pressure coefficients (Cp) are applied with the gust effect factor G. The windward wall uses q_z at each height, and the other surfaces use q_h. Load Case 1 is reported. Roof overhang and parapet pressures can be added for both procedures, and open buildings with free roofs are supported in the Directional Procedure.

Tornado loads (ASCE 7-22 Ch. 32)

For Risk Category III and IV buildings in tornado-prone regions, the calculator checks whether tornado loads are required. The check uses tornado speed (V_T), basic wind speed and exposure category. When they are, tornado pressures are reported separately for C&C and for the Directional Procedure. They are not calculated for the Envelope Procedure or for open buildings.

Assumptions and limitations

The calculator assumes no parapets unless the parapet option is enabled, and Cl. 26.2 low-rise building geometry. In the Directional Procedure, the gust effect factor uses the rigid building method. The area-based reduction of the -1.3 Cp roof coefficient is applied when h/L ≥ 1.0 and the roof slope is under 10°. Results are tabulated by zone and load case, with each output showing its ASCE 7-22 reference.