Wind Load Calculator

Wind pressures on a low-rise building under ASCE 7-22 or 7-16: the main wind force resisting system by the envelope procedure, wall and roof pressures by zone for studs, rafters, sheathing, roofing, windows and doors, and a window and door schedule. Look up the wind speed from an address, or enter it.

Wind speed

Looks up Florida addresses for now. Elsewhere, enter the speed from the ASCE Hazard Tool or your building department.

Site

B suburban, C open, D shoreline
1.0 unless on a hill or ridge
Above sea level; 0 is conservative

Building

Ignored for a flat roof
Partially enclosed: a large opening on one side

Windows and doors Pro

Opening
Width (in)
Height (in)
Velocity pressure42.7 psfqh = 0.00256 Kz Kzt Ke V²
Mean roof height15.0 ftroof 26.6°
Edge strip a4.0 ftend zone 2a = 8.0 ft
Internal pressure±0.18enclosed

Kz = 0.85, Kzt = 1.00, Ke = 1.00, Kd = 0.85 (applied in the pressures, as 7-22 does). Pressures are strength level: positive pushes on the surface, negative pulls away.

Main wind force resisting system

For the frames, shear walls and roof diaphragm, by the envelope procedure for low-rise buildings (ASCE 7-22 Chapter 28, Part 1). Drawn for wind across the ridge, with internal pressure pushing out.

1E13E32E2 Wind
1: +13.4 4: -20.7 2: -10.1 3: -22.8 Pressures in psf, wind from the left

Load case A: wind across the ridge

ZoneGCpfp, +GCpip, −GCpi
10.55+13.4+26.5
2-0.10-10.1+2.9
3-0.45-22.8-9.7
4-0.39-20.7-7.6
1E0.73+19.9+33.0
2E-0.19-13.4-0.4
3E-0.58-27.8-14.7
4E-0.53-26.0-12.9

Load case B: wind along the ridge

ZoneGCpfp, +GCpip, −GCpi
1-0.45-22.9-9.8
2-0.69-31.6-18.5
3-0.37-20.0-6.9
4-0.45-22.9-9.8
50.40+8.0+21.1
6-0.29-17.1-4.0
1E-0.48-24.0-10.9
2E-1.07-45.4-32.3
3E-0.53-25.8-12.7
4E-0.48-24.0-10.9
5E0.61+15.6+28.7
6E-0.43-22.1-9.1

E zones are the end zones, 8.0 ft from the corner that's taken as the reference; check each corner in turn. Zone 2 (2E) suction reaches 20.0 ft from the windward eave; zone 3 (3E) covers the rest. Also check the minimum load case, 16 psf on walls and 8 psf on the roof, and the torsional load cases where they apply.

Walls: components and cladding

For studs, sheathing, siding, windows and doors. Shown for a 10 ft² element; larger elements see less.

Long wall, positive / suction 4 5 5 a = 4.0 ft Zone 4: +42.8 / -46.5 psf Zone 5: +42.8 / -57.4 psf

Window and door schedule Pro

The window and door schedule lists each opening's design pressures in the middle of a wall and near a corner, at strength level and at the allowable stress level that window and door ratings use.

Roof: components and cladding

For rafters, trusses, sheathing, roofing and their fasteners (ASCE 7-22 Figure 30.3-2C). Shaded by suction on a 10 ft² element.

Roof plan, ridge across 112222233 60 × 40 ft; a = 4.0 ft
ZoneEffective wind area, psf (GCp)
10 ft²20 ft²50 ft²100 ft²
1-61.0 (-1.50)-55.1 (-1.34)-47.3 (-1.12)-41.5 (-0.96)
2-97.3 (-2.50)-83.1 (-2.11)-64.3 (-1.59)-50.1 (-1.20)
3-115.4 (-3.00)-98.0 (-2.52)-74.8 (-1.88)-57.4 (-1.40)
All, positive+28.3 (0.60)+25.8 (0.53)+22.5 (0.44)+19.9 (0.37)

Suction with internal pressure pushing out, positive with it pulling in, and no less than 16 psf. The effective wind area is the span times the width carried, with the width at least a third of the span: about 10 ft² for sheathing fasteners, more for rafters and trusses. Overhangs aren't included.

For enclosed and partially enclosed buildings with a mean roof height of 60 ft or less, no taller than they are wide, on regular plans. Doesn't cover open buildings, monoslope or mansard roofs, overhangs, rooftop equipment, or tornado loads (ASCE 7-22 Chapter 32).

How the pressures are worked out

  1. Velocity pressure at the mean roof height h: qh = 0.00256 Kz Kzt Kd Ke V². Kz grows with height and with more open exposure; Kd = 0.85 for buildings. ASCE 7-22 moved Kd from qh into the pressure equations; the pressures come out the same.
  2. Main wind force resisting system: p = qh [(GCpf) − (GCpi)], with the external coefficients GCpf by zone and roof angle, and the internal pressure GCpi taken both ways.
  3. Components and cladding: p = qh [(GCp) − (GCpi)], with GCp falling as the element's effective wind area grows, and no less than 16 psf.

Wind speed maps give strength-level speeds, so these pressures are strength level. Window and door ratings are allowable stress level: compare them with 0.6 times the strength pressure.

Designing the members

These pressures are the strength-level wind load W in the ASCE 7 load combinations. For a beam, girt, rafter or header, multiply the pressure by the width it carries and enter it as wind in the beam designer. For a post or column, enter the wind load it takes in the column designer. Both apply 1.0W for LRFD and 0.6W for ASD.

Exposure categories

  • Exposure B: Urban and suburban areas, wooded areas, with many closely spaced obstructions the size of a house or larger.
  • Exposure C: Open terrain with scattered obstructions under 30 ft: flat open country and grassland.
  • Exposure D: Flat, unobstructed areas and water surfaces: shorelines facing open water, mud flats, salt flats.

Look upwind in each direction. With the envelope procedure, design for the exposure that gives the highest loads from any direction. In Florida's High-Velocity Hurricane Zone (Miami-Dade and Broward) the code requires Exposure C or D. See the Florida wind speed map for the speeds there.

Risk categories

  • I: Low hazard to people: barns, sheds, minor storage, screen enclosures
  • II: Most buildings: homes, offices, stores, warehouses
  • III: Many people or vulnerable people: schools, theaters, larger assemblies
  • IV: Essential: hospitals, fire and police stations, emergency shelters

The risk category picks which wind speed map applies; enter the speed for your building's category.