How to Calculate Wind Loads on a Building — ASCE 7-22, Step by Step

Wind load is the pressure that moving air puts on a building's surfaces, and the force those pressures add up to. In the United States it is calculated with ASCE 7-22: you find the site's basic wind speed, turn it into a velocity pressure, turn that into a design pressure on every wall and roof surface, multiply each pressure by the area it acts on, and check the result against the code's minimum load.

That is the whole method. The rest of this page does it with real numbers on a two-story gable-roof house, following the steps the code lists in ASCE 7-22 Table 27.2-1 and then carrying the pressures to the base shear and the minimum load, and explains each choice on the way. Every number comes from the calculation engine that runs StructSuite's free Wind Loads module — the same numbers as the full Chapter 27 worked example, where every surface and load case is carried to the end.

#What "wind load" means: MWFRS and components and cladding

ASCE 7-22 calculates wind load for two different things, and the first decision is which one you are designing. The definitions in §26.2:

• Main wind force resisting system (MWFRS): "An assemblage of structural elements assigned to provide support and stability for the overall building or other structure. The system generally receives wind loading from more than one surface." — the shear walls, diaphragms, frames and foundation that hold the whole building up against the wind.
• Components and cladding (C&C): "Elements of the building envelope or elements of building appurtenances and rooftop structures and equipment that do not qualify as part of the MWFRS." — roof sheathing, siding, windows, doors, and the studs, rafters and fasteners that hold them.

The two start from the same velocity pressure but use different pressure coefficients. C&C pressures are highest at roof edges and corners and depend on the element's effective wind area, so a C&C pressure is normally larger than the MWFRS pressure on the same surface. This page is the MWFRS calculation — the one that gives the base shear for the lateral system.

#Which ASCE 7-22 procedure to use

Chapter 28's own User Note says that for the buildings it covers, the Envelope Procedure "generally yields the lowest wind pressure of all the analytical methods specified in this standard." Chapter 27 has no height limit, which is why it is the method you can always fall back on and the one this page follows. A house like the one below qualifies for both; whichever you pick, use one procedure for the whole MWFRS calculation. The Chapter 28 worked example runs the Envelope Procedure on a similar house.

#The building

A two-story wood-frame house with a gable roof:

#Step 1 — Risk Category and basic wind speed V

Table 27.2-1 starts with the Risk Category (Table 1.5-1) — an ordinary house is Risk Category II — because the wind speed map depends on it. §26.5.1 assigns one map per category (Figure 26.5-1A for I through 26.5-1D for IV) and permits, as an alternative, the basic wind speeds "from the ASCE Wind Design Geodatabase", which the ASCE 7 Hazard Tool serves by address. That is how you get the wind speed for a zip code or a street address: enter the site and the Risk Category, read V.

V is a 3-second gust speed at 33 ft above ground in Exposure C (§26.2). This house uses V = 100 mph.

#Step 2 — The wind load parameters

With V in hand, Chapter 26 supplies seven more parameters before any pressure can be computed (Table 27.2-1, Step 3; §27.2.1 lists them with V). For this house:

Exposure is the choice that moves the result most, and §26.7 sets it from the ground surface roughness upwind of the site:

• Exposure B — Surface Roughness B (urban and suburban areas, wooded areas, numerous closely spaced obstructions the size of single-family dwellings or larger) prevails upwind for more than 1,500 ft, for a building with h ≤ 30 ft. Most residential subdivisions.
• Exposure D — Surface Roughness D (flat, unobstructed areas and water surfaces) prevails upwind for more than 5,000 ft or 20 times the building height, whichever is greater.
• Exposure C — "shall apply for all cases where Exposure B or D does not apply": open terrain with scattered obstructions generally under 30 ft high, open country, grasslands.

The full Chapter 27 example has excerpts of Table 26.6-1, Table 26.10-1 and Table 26.13-1; the Wind Loads module shows each table in the code's own layout with the selection highlighted.

#Step 3 — Velocity pressure q_z (Eq. 26.10-1)

q_z = 0.00256 · K_z · K_zt · K_e · V² (psf, with V in mph)

Where 0.00256 comes from. It is Bernoulli's dynamic pressure, ½ρV², for standard air with V converted from mph to ft/s — ASCE 7-22 Commentary §C26.10.2 derives it: ½ × 0.002378 × (V × 88/60)² = 0.00256 V² psf, where 0.002378 is the density of standard air in foot-pound-second units and 88/60 converts mph to ft/s. A "wind load calculator" that stops at 0.00256 V² × area has computed only this term; the code then adjusts it for height and terrain (K_z), topography (K_zt), altitude (K_e), and in the next step for direction (K_d), gusts (G) and the shape of the building (C_p).

K_z comes from Table 26.10-1. For Exposure C the table gives 0.90 at 20 ft and 0.94 at 25 ft, so at the mean roof height:

K_h = 0.90 + (22 − 20)/(25 − 20) × (0.94 − 0.90) = 0.916

q_h = 0.00256 × 0.916 × 1.0 × 1.0 × 100² = 23.45 psf

q_h (q_z at z = h) is the value the leeward wall, the sidewalls, the roof and the internal pressure all use. Only the windward wall uses q_z at each height z — for this house 21.76 psf from grade to 15 ft (the 0–15 ft row of Table 26.10-1, K_z = 0.85), 22.53 psf at the 18-ft eave, and up to 24.27 psf at the 26-ft ridge on the gable end when the wind blows along the ridge.

#Step 4 — Design pressure p on each surface (Eq. 27.3-1)

p = q · K_d · G · C_p − q_i · K_d · (GC_pi)

q = q_z on the windward wall and q_h everywhere else; for an enclosed building q_i = q_h. The first term is the outside air pushing on (positive) or pulling off (negative) the surface; the second is the air inside the building doing the same from the other side.

External pressure coefficients C_p come from Figure 27.3-1. On the walls: +0.8 windward, −0.7 on the sidewalls, and on the leeward wall a value set by the building's depth along the wind, L/B — here −0.5 with the wind across the ridge (L/B = 32/48 = 0.67).

Windward wall at z = h = 22 ft:

p = 23.45 × 0.85 × 0.85 × 0.8 − 23.45 × 0.85 × (±0.18) = +9.97 psf (with +GC_pi) or +17.14 psf (with −GC_pi)

Leeward wall, wind across the ridge:

p = 23.45 × 0.85 × 0.85 × (−0.5) − 23.45 × 0.85 × (±0.18) = −12.06 psf (+GC_pi) or −4.88 psf (−GC_pi)

Every surface is computed twice, once for each sign of GC_pi, because the inside of the building can be pressurized or under suction and different elements are governed by different signs. The roof gets its own coefficients by slope and h/L (for this 6:12 roof the windward slope has two, −0.33 and +0.15, and both are checked), and the wind is run in both directions — across the ridge and along it. The full Chapter 27 example tabulates every surface for both.

#Step 5 — From pressure to force: base shear

A pressure becomes a force when it is multiplied by the area it acts on: F = p × A. For the lateral system the number that matters is the base shear in each direction:

• the windward wall pushes and the leeward wall pulls, both in the direction of the wind, so their forces add;
• the internal pressure acts equally on the inside of both walls, so GC_pi cancels from the base shear;
• for a roof slope of 10° or more, the horizontal component of the roof pressures is included (for this house it adds to the shear).

For this house the engine gives, at full design pressure (Load Case 1 of Figure 27.3-8):

Chapter 27 does not stop at one direction at full pressure. §27.3.5 requires the four design wind load cases of Figure 27.3-8: full pressure on each axis alone, 75% with a torsional moment, 75% on both axes at once, and 56.3% on both axes with torsion. For this house Case 1 governs the base shear and Cases 3 and 4 govern the roof uplift (21,125 lb). The Chapter 27 example works all four. An exception to §27.3.5 lets buildings that meet Section D.1 of Appendix D be designed for Cases 1 and 3 only — Appendix D exempts, among others, buildings of two stories or fewer framed with light-frame construction, which includes this house; check its conditions before dropping Cases 2 and 4.

#Step 6 — Check the minimum design wind load (§27.1.5)

ASCE 7-22 sets a floor under the calculated pressures. §27.1.5 requires the MWFRS wind pressure of an enclosed or partially enclosed building to be not less than 16 psf multiplied by the wall area and 8 psf multiplied by the roof area, both projected onto a vertical plane normal to the assumed wind direction, with the wall and roof loads applied simultaneously.

With the wind along the ridge, the triangular gable end is wall, so the whole end silhouette takes 16 psf. Here the calculated loads are larger in both directions, so they govern. The minimum depends only on the silhouette, not on wind speed or exposure: build the same house in Exposure B and the Case 1 base shears drop to 15,783 lb and 9,376 lb, below the minimums, which then govern both directions.

#Step 7 — Strength level W, or 0.6W for allowable stress design

ASCE 7-22 wind loads are strength-level (W). The allowable stress design combinations of §2.4.1 use 0.6W (for example combination 5a, D + 0.6W). For this house:

The wood shear wall guide shows how a base shear like this is distributed to the walls and designed.

#Mistakes that get a wind calculation returned

• K_d counted twice. In ASCE 7-22, Eq. 26.10-1 has no K_d; it appears in the pressure equation (Eq. 27.3-1). Spreadsheets that also put it in q_z apply it twice.
• Exposure read from the site instead of upwind. §26.7 looks at the ground surface roughness upwind of the building. A house on an open lot inside a subdivision is usually Exposure B; a house facing open fields or water may be C or D.
• Only one GC_pi sign. Walls and roofs each need both columns; the larger wall load comes from −GC_pi, the larger suction from +GC_pi.
• C&C pressures used for the MWFRS, or the reverse. The shear walls and diaphragms get Chapter 27 or 28 loads; sheathing, studs and fasteners get Chapter 30 pressures for the wind acting on them directly. Some elements need both — Commentary C26.2: "Components can be part of the MWFRS when they act as elements in shear walls or roof diaphragms, but they may also be loaded directly by wind as individual elements."
• Mixing the two MWFRS procedures. Chapter 27 C_p values and Chapter 28 GC_pf zones belong to different methods; one calculation uses one.
• Skipping the minimum. At low wind speeds, in Exposure B and on long, low buildings, the §27.1.5 floor often governs.
• Stopping at 0.00256 V² × area. That is the dynamic pressure of the wind, not the design pressure of a building.

#Summary of results

#Frequently Asked Questions

#What is wind load?

Wind load is the pressure moving air exerts on a building — pushing on the windward wall, pulling on the leeward wall, sidewalls and usually the roof — and the force those pressures add up to. ASCE 7-22 calculates it for the main wind force resisting system (the structure as a whole) and separately for components and cladding (the envelope and its fasteners).

#What is the formula for wind load?

Under ASCE 7-22 Chapter 27 it is two equations: the velocity pressure q_z = 0.00256 K_z K_zt K_e V² (Eq. 26.10-1, psf with V in mph), then the design pressure p = q K_d G C_p − q_i K_d (GC_pi) (Eq. 27.3-1) on each surface. The force on a surface is p times its area, and the result is checked against the §27.1.5 minimum of 16 psf on walls and 8 psf on the roof's projected area. Chapter 28 replaces Eq. 27.3-1 with p = q_h K_d [(GC_pf) − (GC_pi)].

#How do I find the wind load requirements for my zip code or address?

What varies by location is the basic wind speed V. Read it from the ASCE 7-22 maps (Figure 26.5-1, one map per Risk Category) or, as §26.5.1 permits, from the ASCE Wind Design Geodatabase through the ASCE 7 Hazard Tool: enter the address and the Risk Category and it returns V. Everything else — exposure, topography, the building's shape — is decided for the specific building, so there is no single "wind load for a zip code"; V goes into the steps on this page. Your local building department may also adopt a design wind speed or amendments, so check the jurisdiction's adopted code.

#Is wind load the same as wind pressure?

No. Pressure is force per unit area (psf) on one surface; wind load usually means the resulting force (lb) on a surface or on the whole building. For this house the design pressures are about 10 to 17 psf on the windward wall, and the base shear they produce is 23,089 lb across the ridge.

#What is a typical wind load on a house in psf?

There is no single value — it depends on wind speed squared, exposure and height. For this two-story house at V = 100 mph in Exposure C, q_h is 23.45 psf and the MWFRS wall pressures are roughly +9 to +18 psf windward and −3 to −15 psf on the leeward and side walls. In Exposure B the same house has q_h = 16.28 psf (Chapter 27). Individual surface pressures can be lower than 16 psf; what §27.1.5 limits is the total MWFRS load, which is never less than 16 psf × the projected wall area plus 8 psf × the projected roof area.

#Does this cover components and cladding?

No. This is the MWFRS calculation. Components and cladding — sheathing, siding, windows, doors, rafters, studs and their fasteners, for the wind acting on them directly — use Chapter 30, which starts from the same q_h but uses zone coefficients that depend on the element's effective wind area and are highest at roof edges and corners. StructSuite's wind module computes the MWFRS pressures only.

#Should I use the directional or the envelope procedure?

Chapter 27 (Directional) works for buildings of all heights; Chapter 28 (Envelope) is limited to low-rise buildings with flat, gable or hip roofs and, by its own User Note, generally gives the lowest MWFRS pressures for them. For a house that qualifies for both, either is acceptable — use one consistently. See the Chapter 28 worked example for the envelope method on a similar house.

#Can I calculate wind loads for free?

Yes. StructSuite's Wind Loads module runs both MWFRS procedures of ASCE 7-22 — Chapter 27 and Chapter 28 — free in the browser, with every equation substituted and the code table behind each value shown. Printing the calculation report is part of the Pro plan.

#Where to go next

• Every surface, both wind directions and all four load cases on this house: How to Calculate Wind Loads — Directional Procedure (ASCE 7-22 Chapter 27)
• The envelope method on a 60 × 30 ft house: How to Calculate Wind Loads — Envelope Procedure (ASCE 7-22 Chapter 28)
• Carry the base shear into the walls: How to Design a Wood Shear Wall (SDPWS 2021)
• Run your own building: StructSuite's Wind Loads module