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ASCE 7 builds wind pressure from the basic speed squared, scaled by exposure/height (Kz), topography (Kzt), directionality (Kd), then a gust factor G and pressure coefficient Cp for the surface. The full method has many cases; the simplified velocity pressure below is a sanity check, not a design.
- V = 120 mph, exposure C, ~30 ft.
- qz = 0.00256 × 0.98 × 0.85 × 120² ≈ 30.7 psf.
- p ≈ 21 psf on the windward wall.
Reference tables
Basic velocity pressure qz (Kz=1, Kd=0.85), psf
| V (mph) | qz |
|---|---|
| 90 | 17.6 |
| 110 | 26.3 |
| 120 | 31.3 |
| 140 | 42.6 |
| 160 | 55.7 |
Exposure height factor Kz (exposure C)
| Height (ft) | Kz |
|---|---|
| 15 | 0.85 |
| 30 | 0.98 |
| 50 | 1.09 |
| 100 | 1.26 |
A number the tables do not give: at a 120 mph basic wind speed, expect roughly 30 psf of velocity pressure near 30 ft in exposure C.
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FAQ
Is this a code-compliant wind design?
No. It shows the velocity pressure trend; a real design applies the full ASCE 7 method with all coefficients, load cases and directions.
What is Kz?
The exposure/height factor — it grows with height and with more open terrain (exposure C/D vs B).
Velocity pressure vs design pressure?
Velocity pressure (qz) is the raw stagnation pressure; design pressure multiplies it by the gust factor and pressure coefficient for the actual surface.
Which wind speed do I use?
The basic wind speed from the ASCE 7 maps for your site and risk category — it already includes the appropriate return period.
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