Wind Load Calculator

Calculate design wind pressures per ASCE 7-22 directional procedure (Chapter 27). Velocity pressure qh, gust factor G, and pressure coefficients Cp for windward wall, leeward wall, sidewalls, and roof.

ASCE 7-22 · US standard · results shown in both psf and kPa

Site & Wind Speed

mph
144.8 km/h
ft
9.1 m
1.0 = flat, up to 1.5 for hilltop

Building Parameters

II — Iw = 1
0.85 for buildings (ASCE 7)
0.85 for rigid buildings (f > 1 Hz)
°
Affects Cp roof
0.18 enclosed, 0.55 partial

Wind Pressure Results

Kh = 0.98qh = 17.273 psf (827 Pa)Iw = 1
Windward wall (Cp = +0.8)
+9.1 psf+0.436 kPa
Leeward wall (Cp = −0.5)
-4.7 psf-0.225 kPa
Side walls (Cp = −0.7)
-7.63 psf-0.365 kPa
Roof windward (slope 10°, Cp = -0.7)
-7.63 psf-0.365 kPa

Positive (+) = pressure toward surface (inward). Negative (−) = suction away from surface (outward). All values are net (external − internal). Leeward and sidewall/roof suctions act simultaneously with windward pressure — combine for lateral load.

Engineering Reference

ASCE 7-22 Velocity Pressure Equation

qz = 0.00256 × Kz × Kzt × Kd × V² (psf, V in mph)
qz = 0.613 × Kz × Kzt × Kd × V² (Pa, V in m/s)

Design pressure: p = qh × G × Cp − qi × (±GCpi)

The basic wind speed V is the 3-second gust speed at 33 ft (10 m) above ground in open terrain with 700-year mean recurrence interval (Risk Category II). ASCE 7-22 replaced the earlier 50-year MRI maps — wind speeds are higher but importance factors for standard occupancy are 1.0.

Exposure Categories

Exposure B: Surface roughness B — urban/suburban areas, wooded areas, or terrain with closely spaced obstructions the size of single-family dwellings or larger
Exposure C: Open terrain with scattered obstructions having heights generally less than 30 ft (9.1 m); flat open country and grasslands; all cases between exposures B and D
Exposure D: Flat, unobstructed areas exposed to wind flowing over open water for a distance of at least 1 mile (1.6 km); coastal hurricane zones

Note: Exposure A (large city centres) was removed in ASCE 7-02. There is no Exposure A in ASCE 7-10 onwards. For dense urban environments, use Exposure B with reduced Kz values from Table 26.6-1.

Worked Example — 90 mph, 30 ft, Exposure C

V = 90 mph, h = 30 ft, Exposure C, Risk Cat II (Iw = 1.0)
Kh (Table 26.6-1, Exp C, 30 ft) = 0.98
Kzt = 1.0 (flat), Kd = 0.85, G = 0.85

qh = 0.00256 × 0.98 × 1.0 × 0.85 × 90² = 17.3 psf (828 Pa)

Windward wall (Cp=0.8, Cpi=0.18):
p = 17.3 × 0.85 × 0.8 − 17.3 × 0.85 × 0.18 = 11.75 − 2.64 = +9.1 psf (+0.44 kPa)

Leeward wall (Cp=−0.5):
p = 17.3 × 0.85 × (−0.5) − 17.3 × 0.85 × (−0.18) = −7.35 + 2.64 = −4.7 psf (−0.22 kPa)

How Wind Loads Are Transferred Through a Structure

Wind pressure acts on the building envelope — walls, roof, and cladding — and must be transferred through the structural system to the foundations. The load path is: cladding panels → girts and purlins (secondary members) → columns and rafters (primary frames) → bracing and shear walls → foundation. Each element must be designed for the tributary wind load it attracts.

Roof uplift is often the governing load for low-rise buildings. The combination of positive windward wall pressure pushing inward and negative (suction) roof pressure pulling upward can exceed gravity loads in high-wind regions. Connections between roof diaphragm, wall top plates, and columns must be designed as continuous load paths — this is the primary cause of roof failures in hurricanes when straps or anchors are undersized.

Components and Cladding vs. Main Wind Force Resisting System

ASCE 7 distinguishes two load cases. The Main Wind Force Resisting System (MWFRS) is the structural assembly that resists the overall lateral force and overturning moment — typically moment frames, braced frames, or shear walls. MWFRS pressures use the G·Cp method with external Cp values from ASCE 7 Figure 27.3-1.

Components and Cladding (C&C) covers individual elements: windows, cladding panels, fasteners, purlins, and girts. C&C pressures are generally higher than MWFRS pressures because small tributary areas experience higher local suctions, particularly at building corners, eave edges, and ridge lines. Always check both C&C and MWFRS — the governing case differs by element type.

Common Mistakes in Wind Load Calculations

  • Wrong wind speed map: ASCE 7-10 and later editions use ultimate (LRFD) wind speeds. Earlier editions (ASCE 7-05) used allowable stress design speeds. Mixing editions produces unconservative results.
  • Flat terrain assumption: If the site has hills, ridges, or escarpments within 2 miles, the topographic factor Kzt may increase design pressure by 10–40%.
  • Ignoring internal pressure: Open or partially enclosed buildings see large internal pressure coefficients (GCpi = ±0.55). Failing to add internal pressure to external suction understates net uplift on roofs.
  • Single design pressure for all cladding: Corner zones have substantially higher C&C pressures than field zones. Apply zonal pressures to the corresponding tributary areas.

Disclaimer

Wind load calculations are complex and jurisdiction-dependent. This calculator implements simplified ASCE 7 procedures and is intended for preliminary estimation and educational purposes only. Structural design must be performed by a licensed structural engineer in accordance with the applicable building code for the project location.

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