ASCE 7-22 Wind: MWFRS Design Pressure for Residential Gable Roof

Example

A Risk Category II single-family home is 40 ft × 28 ft in plan with 20 ft mean roof height, 6:12 roof slope. Basic wind speed 115 mph, Exposure B. Determine MWFRS design pressures for roof and wall zones per ASCE 7-22 Chapter 28.

How StructSuite solves this

StructSuite's free structural design software applies ASCE 7-22 Chapter 28: velocity pressure qh (Eq 26.8-1), external pressure coefficients GCpf from Figure 28.3-1 for gable roofs, internal pressure GCpi. Design pressure p = qh × Kd × (GCpf − GCpi). Step 6 provides zone pressures; Step 7 shows full design pressure table for each zone and load case. Critical for roof truss and wall stud design.

Steps

1. Step 1: Determine risk category of building

   Design consideration: Residential Risk II. 115 mph inland; 130–150 mph coastal. q ∝ V²: 30% speed increase = 70% pressure increase. Hurricane clips, straps sized from zone pressures. Address or zip for ASCE 7 Figure 26.5-1.

   In StructSuite: In Step 1, use the Risk Category dropdown to select I, II, III, or IV (e.g., II for offices, residential). In the Basic Wind Speed (mph) input box enter 115. Per ASCE 7-22 §26.2, Figure 26.5-1. If using address lookup, use the address search to auto-fill wind speed.

2. Step 4: Velocity pressure exposure coefficient

   Design consideration: 40×28 ft, h=20 ft—low-rise Ch 28. Roof angle 6:12: Zone 2 (field) and 2E (edge) often critical for uplift. Zone size a = 0.1×least plan dimension. Steeper roof: different GCpf; 4:12–9:12 common for gable.

   In StructSuite: In the Building dimensions section, in Building Length (ft) enter 40; in Building Width (ft) enter 28; in Mean Roof Height (ft) enter 20. These drive Kh from ASCE 7-22 Table 26.10-1.

3. Step 3: Wind load parameters

   Design consideration: B typical suburban. C (open lot, new development): 25–35% higher. Enclosed: GCpi=±0.18. Partial enclosure (garage door open): higher internal pressure. Kzt for hillside—ridge sites can double wind.

   In StructSuite: In Step 3, use the Exposure dropdown to select B, C, or D. If ground elevation > 1000 ft, use Table 26.9-1 for Ke. For topographic features (hills, ridges), use the Kzt section and enter parameters from ASCE 7-22 Figure 26.8-1. Kd = 0.85 for MWFRS is typical.

4. Step 5: Velocity pressure at mean roof height

   Design consideration: Zone 2/2E uplift drives roof-to-wall and wall-to-foundation connections. Higher qh = more clips, larger straps. Residential: truss-to-plate, stud-to-plate. Design pressure p = qh(GCpf − GCpi) for each zone.

   In StructSuite: In Step 5, the velocity pressure qh is auto-calculated from ASCE 7-22 Eq 26.8-1. Review the displayed value. Open Step 6 for external pressure coefficients (load cases 1–4); open Step 7 for design pressure results by zone.

Live design (pre-filled)

The form below is the real StructSuite module with example data loaded. Display only—values cannot be changed.