Wind Load Workflow

Educational guide for wind pressure estimation and documenting assumptions: exposure, height, coefficients, internal pressure.

Wind loading is one of the most parameter-sensitive inputs in structural design. Small changes in terrain category, building height, or pressure coefficient can shift the design wind pressure by 20-50%. Unlike gravity loads (which are relatively stable), wind loads depend on geographic location, surrounding terrain, building geometry, and internal pressure assumptions — all of which require explicit documentation.

This page outlines the typical wind load estimation workflow and highlights where assumptions need to be recorded. It is written as an educational guide, not as a wind engineering procedure.

For the full general verification workflow (units, replication strategy, sensitivity testing, and archiving), see How to verify calculator results.

Before You Start

Before computing any wind pressure, gather:

Site location and wind speed: The basic wind speed from the applicable wind map (ASCE 7-22 Fig. 26.5-1 for US, AS/NZS 1170.2 Table 3.1 for Australia). Know the return period (Risk Category II = 700-yr MRI for ASCE 7-22; ultimate limit state for AS 1170.2).
Wind speed averaging interval: ASCE 7 uses 3-second gust speed. AS/NZS 1170.2 uses regional wind speed with direction and terrain multipliers. EN 1991-1-4 uses 10-minute mean speed. These are not interchangeable — converting between them requires the Durst curve or standard-specific factors.
Terrain/exposure category: Describe the surrounding terrain within 1-2 km upwind of the site. ASCE 7: Exposure B (urban/suburban), C (open), D (flat/water). AS/NZS 1170.2: Terrain Category 1 (very exposed) to 4 (urban CBD).
Building geometry: Plan dimensions, mean roof height, roof slope, and whether the building is enclosed, partially enclosed, or open. This classification drives internal pressure coefficients.
Topographic features: Nearby hills, ridges, or escarpments may amplify wind speed. ASCE 7 uses Kzt; AS/NZS 1170.2 uses Mt.
Openings and enclosure classification: Count and locate all openings (doors, windows, louvers). A single large opening on the windward wall can change the building from "enclosed" to "partially enclosed," increasing internal pressure dramatically.

Step-by-Step Design Process

Step 1 — Determine the basic wind speed V. From the wind map for the site's Risk Category and return period. ASCE 7-22: V ranges from 95 mph (low-wind interior) to 180+ mph (hurricane coast). AS/NZS 1170.2: regional wind speed VR from Table 3.1 for the required return period.

Step 2 — Compute velocity pressure. Per ASCE 7-22 Section 26.10: qz = 0.00256 Kz Kzt Kd Ke V^2 (psf), where Kz = velocity pressure exposure coefficient (varies with height and exposure), Kzt = topographic factor, Kd = wind directionality factor (0.85 for buildings), Ke = ground elevation factor.

Step 3 — Determine external pressure coefficients. For the MWFRS (main wind force resisting system): use ASCE 7 Figure 27.3-1 for enclosed/partially enclosed buildings. Windward wall: Cp = 0.80. Leeward wall: Cp = -0.20 to -0.50 (depends on L/B ratio). Side walls: Cp = -0.70. Roof: varies with slope and zone.

Step 4 — Determine internal pressure coefficient. Enclosed buildings: GCpi = +/- 0.18. Partially enclosed buildings: GCpi = +/- 0.55. The internal pressure is applied uniformly to all interior surfaces and combined with the external pressure to find the net design pressure.

Step 5 — Compute design wind pressure. For the MWFRS: p = q GCp - qi (GCpi), where G = gust effect factor (0.85 for rigid buildings per ASCE 7). For C&C (components and cladding): use the appropriate figure (ASCE 7 Chapter 30) with zone-specific GCp values (zones 1-5 for walls, zones 1-3 for roofs).

Step 6 — Apply to structural members. Multiply the design pressure by the tributary area for each member. Combine with other loads per the governing load combination standard (ASCE 7 Section 2.3 LRFD or 2.4 ASD).

Step 7 — Document all parameters. Record wind speed, exposure, Kz profile, Kzt, Kd, Ke, internal pressure classification, and all pressure coefficients with their zone designations.

Worked Example

Given: A single-story industrial building, 80 ft x 120 ft plan, 25 ft eave height, 5:12 roof slope (22.6 degrees), enclosed, no topographic effects, Exposure C, Risk Category II. Location: Dallas, TX.

Step 1 — Basic wind speed: ASCE 7-22 Figure 26.5-1B (Risk Cat. II): V = 115 mph for Dallas.

Step 2 — Velocity pressure at mean roof height (h = 25 + 0.5 x 40 x tan(22.6) = 25 + 8.3 = 33.3 ft, use h = 33 ft):

Kz at 33 ft, Exposure C: from ASCE 7 Table 26.10-1, interpolate: Kz = 1.00
Kzt = 1.0 (flat terrain)
Kd = 0.85
Ke = 1.0 (sea level)
qh = 0.00256 x 1.00 x 1.0 x 0.85 x 1.0 x 115^2 = 0.00256 x 0.85 x 13,225 = 28.8 psf

Step 3 — External pressure coefficients (MWFRS, wind normal to 80-ft wall):

Windward wall: Cp = +0.80
Leeward wall (L/B = 120/80 = 1.5): Cp = -0.33
Side walls: Cp = -0.70
Windward roof (slope 22.6 degrees, h/L = 33/80 = 0.41): Cp = -0.20 to +0.20 (use -0.20 for uplift case)
Leeward roof: Cp = -0.60

Step 4 — Internal pressure: Enclosed building: GCpi = +/- 0.18. qi = qh = 28.8 psf (for all heights).

Step 5 — Design pressures (MWFRS, G = 0.85):

Windward wall: p = 28.8 x 0.85 x 0.80 - 28.8 x (-0.18) = 19.6 + 5.2 = 24.8 psf
Leeward wall: p = 28.8 x 0.85 x (-0.33) - 28.8 x (+0.18) = -8.1 - 5.2 = -13.3 psf (suction)
Windward roof: p = 28.8 x 0.85 x (-0.20) - 28.8 x (+0.18) = -4.9 - 5.2 = -10.1 psf (net uplift)

Step 6 — Total lateral force on 80-ft frame (per foot of building length):

Net windward + leeward pressure = 24.8 + 13.3 = 38.1 psf
Total base shear per foot of building = 38.1 x 33 / 1000 = 1.26 klf

Result: Design wind pressure of 28.8 psf (qh) with net lateral frame pressure of 38.1 psf. Use for portal frame or braced frame design.

Common Pitfalls

Mixing wind speed averaging intervals. Using an ASCE 7 3-second gust speed with AS/NZS 1170.2 multipliers (or vice versa) without conversion. A 115 mph 3-second gust is roughly equivalent to a 90 mph 10-minute mean. Mixing these produces 60%+ errors.
Wrong exposure category. A suburban site (Exposure B) has lower wind pressures than an open site (Exposure C). Using Exposure C when B applies is conservative by 15-25%. Using B when the site has open fetch is unconservative by the same margin.
Ignoring internal pressure. For enclosed buildings, GCpi = +/- 0.18 adds or subtracts about 5 psf from every surface. For partially enclosed buildings, GCpi = +/- 0.55 — this can be the dominant load on windward walls and roof uplift. Misclassifying enclosure is the single largest error in wind load calculations.
Using MWFRS pressures for cladding design. The MWFRS procedure averages pressure over large areas. Components and cladding (C&C) pressures at edges and corners can be 2-3 times higher due to local flow separation. Always use Chapter 30 for cladding, not Chapter 27.
Neglecting topographic effects. Buildings on or near hill crests, ridges, or escarpments experience amplified wind speeds. The Kzt factor can increase pressure by 50-100% in extreme topography. Ignoring it is unconservative.
Not checking all wind directions. The critical design case may come from wind perpendicular to the long wall, the short wall, or diagonally. Check all applicable directions, especially for asymmetric buildings.

Code Comparison

Parameter	ASCE 7-22	AS/NZS 1170.2-2021	EN 1991-1-4	NBC / CSA
Wind speed type	3-second gust	Regional 3-sec gust (but with different multipliers)	10-minute mean	Hourly mean (1/50 year)
Reference height	Mean roof height h	Average roof height h	Reference height ze	Reference height
Exposure/terrain	B, C, D	TC 1, 1.5, 2, 2.5, 3, 4	Terrain categories 0, I, II, III, IV	Open, rough, urban
Velocity pressure formula	q = 0.00256 Kz Kzt Kd Ke V^2	qz = 0.5 rho [V Md Mz Mt Ms]^2	qp(z) = 0.5 rho v_b^2 ce(z)	q = Cv Ce Ct Cg q_ref
Internal pressure (enclosed)	GCpi = +/- 0.18	Cpi = -0.2 or 0.0 (Table 5.1)	cpi from Table 7.1 (EN)	Cpi = +/- 0.15 to 0.45
Gust factor (rigid)	G = 0.85	Cfig x Cdyn (Cdyn = 1.0 for rigid)	cs cd per Section 6	Cg = 2.0 (gust factor)
Directionality	Kd = 0.85 (buildings)	Md from Table 3.2 per direction	cdir from NA (typically 1.0)	Included in q_ref
C&C zone factors	Zones 1-5 walls, 1-3 roof	Ka (area reduction) per Table 5.4	cpe,1 and cpe,10 per area	Zone-specific GCp

Step 1 — Establish the basic wind speed

Determine the reference wind speed for the site (from the applicable wind map or standard).
Record the return period / importance level used.
Note whether the wind speed is a 3-second gust, 10-minute mean, or hourly mean — different standards use different averaging intervals, and they are not interchangeable.

Step 2 — Select terrain and exposure category

Terrain/exposure category selection rationale should be documented with a description of the surrounding conditions.
Terrain can change over the building's lifetime (e.g., surrounding development). Some codes require consideration of the most unfavorable plausible exposure.
If the site is near a terrain transition (e.g., suburban to open), the applicable rules for transition zones should be considered.

Step 3 — Determine height and geometry factors

Height reference and whether the building geometry changes with height.
For tall buildings, wind pressure increases with height and varies across the facade — a single pressure value may not be sufficient.
Record whether the factors are based on the mean roof height or the height at the point of interest.

Step 4 — Apply pressure coefficients

External and internal pressure coefficient assumptions and building permeability assumptions.
Whether local zone pressures are required (edges/corners/ridge) versus global pressures.
For enclosed buildings, internal pressure depends on the opening classification (enclosed/partially enclosed/open) — this classification can dominate the net pressure on some surfaces.
Record which surface or zone each pressure applies to.

Step 5 — Documentation and sensitivity

Treat any quick wind pressure tool as a starting point; final loading should follow the governing wind standard and project-specific zone requirements.
Record the governing wind standard and edition (e.g., ASCE 7-22, AS/NZS 1170.2-2021, EN 1991-1-4).
Wind load parameters interact multiplicatively, so a 10% error in two parameters compounds to ~20% overall. Run a sensitivity check on the most uncertain parameter (usually terrain category or internal pressure).

Frequently Asked Questions

Why do different wind calculators give such different results? The most common reasons are: different wind speed averaging intervals (3-second gust vs 10-minute mean), different terrain/exposure classifications, and different internal pressure assumptions. Always check that these parameters match before comparing results.

What is the difference between ASCE 7 and AS/NZS 1170.2 wind speeds? ASCE 7 uses 3-second gust speeds, while AS/NZS 1170.2 uses regional wind speeds with specific multipliers. The numerical values are not directly comparable without conversion. Do not mix wind speed values between different standards.

Should I use the simplified or the full wind procedure? Most codes offer a simplified procedure for low-rise, regular buildings. If the building is tall, has an unusual shape, is in a special terrain condition, or requires cladding design pressures, the full analytical or wind-tunnel procedure is more appropriate.

Does the calculator handle directional wind analysis? The basic calculator applies wind from the most critical direction. Directional analysis (reducing pressure based on wind direction probabilities) is a more advanced technique that requires additional data and is not included in the simplified tool.

How do wind and seismic loads interact in load combinations? Wind and seismic rarely act simultaneously at maximum intensity, which is why ASCE 7 LRFD load combinations (LC4 and LC6) include wind at 1.0W alongside partial dead and live loads. The designer checks wind and seismic as separate load cases and designs for the governing combination. For most low- to mid-rise buildings, wind governs lateral design in moderate seismic zones; seismic governs in high-seismic regions regardless of wind speed.

What is internal pressure and why does it matter? Internal pressure arises from wind entering through openings in the building envelope and pressurizing the interior. For enclosed buildings with no dominant opening, the net effect on exterior cladding is relatively minor. For partially enclosed buildings (e.g., large garage doors, broken windows), internal pressure can add significantly to windward wall and roof suction forces. Misclassifying a building as enclosed when it should be partially enclosed is a common error that under-estimates net uplift on roof panels.

Is this guide engineering advice? No. It is an educational description of the wind load estimation workflow. Wind loading determination for a real project must follow the governing standard and should be performed by a qualified engineer.

Run This Calculation

→ Wind Load Calculator — ASCE 7 and AS/NZS 1170.2 wind pressure from site parameters, exposure category, and building geometry.

→ Portal Frame Calculator — rafter and column design for portal frames under wind and gravity loads.

→ Load Combinations Calculator — combine wind with dead, live, and snow per ASCE 7-22 LRFD and ASD.

Disclaimer (educational use only)

This page is provided for general technical information and educational use only. It does not constitute professional engineering advice, a design service, or a substitute for an independent review by a qualified structural engineer. Any calculations, outputs, examples, and workflows discussed here are simplified descriptions intended to support understanding and preliminary estimation.

All real-world structural design depends on project-specific factors (loads, combinations, stability, detailing, fabrication, erection, tolerances, site conditions, and the governing standard and project specification). You are responsible for verifying inputs, validating results with an independent method, checking constructability and code compliance, and obtaining professional sign-off where required.

The site operator provides the content "as is" and "as available" without warranties of any kind. To the maximum extent permitted by law, the operator disclaims liability for any loss or damage arising from the use of, or reliance on, this page or any linked tools.