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Wind pressure calculator for glazing
Wind pressure on a facade is the peak velocity pressure multiplied by a shape coefficient. The peak pressure grows with the basic wind speed, with height above ground and with how open the surroundings are. The coefficient depends on where the pane sits: a corner of the building sees far more suction than the middle of a wall. This page works out both, to Eurocode or to ASCE 7, and shows every factor it used.
Eurocode EN 1991-1-4, step by step
| Terrain | z₀ (m) | zmin (m) |
|---|---|---|
| 0 — open sea | 0.003 | 1 |
| I — flat, no vegetation | 0.01 | 1 |
| II — low vegetation | 0.05 | 2 |
| III — suburban | 0.3 | 5 |
| IV — urban | 1.0 | 10 |
External pressure coefficients are the local ones, cpe,1, which apply to loaded areas of 1 m² or less. That is the right column for a pane of glass or a fixing; the cpe,10 values are for whole structural elements and would under-read here.
| Zone | A | B | C | D | E |
|---|---|---|---|---|---|
| cpe,1, h/d ≥ 5 | −1.4 | −1.1 | −0.5 | +1.0 | −0.7 |
| cpe,1, h/d = 1 | −1.4 | −1.1 | −0.5 | +1.0 | −0.5 |
| cpe,1, h/d ≤ 0.25 | −1.4 | −1.1 | −0.5 | +1.0 | −0.3 |
Internal pressure: when the openings cannot be estimated, EN 1991-1-4 says to take the more onerous of cpi = +0.2 and −0.3. That is what "unknown" does here, and it is why the suction figure is bigger than the bare external coefficient would suggest.
Characteristic or design? The value above is characteristic. For an ultimate limit state check you multiply by the partial factor for wind, γQ = 1.5 in the recommended EN 1990 set — and that is the number the thickness calculator wants. Both are shown.
ASCE 7-16, step by step
GCp falls as the effective wind area grows, logarithmically between 10 ft² and 500 ft². For walls on a building up to 60 ft: zone 4 runs from +1.0 / −1.1 down to +0.7 / −0.8, and zone 5 from +1.0 / −1.4 down to the same +0.7 / −0.8. ASCE 7 wind loads are already at strength level, so there is no extra 1.5 to apply — for an allowable stress check you would use 0.6 × the value instead.
Peak velocity pressure by wind speed and height
qp in kN/m² from EN 1991-1-4 for terrain II (low vegetation, z₀ = 0.05 m), flat ground (co = 1.0) and cdir = cseason = 1.0, the same sums as the calculator above. Read across from the basic wind speed of your national annex map. Multiply by cpe − cpi for the pressure on a pane.
| Basic wind speed vb | 5 m | 10 m | 20 m | 50 m |
|---|---|---|---|---|
| 22 m/s (79 km/h) | 0.58 | 0.71 | 0.85 | 1.05 |
| 24 m/s (86 km/h) | 0.69 | 0.85 | 1.01 | 1.25 |
| 26 m/s (94 km/h) | 0.82 | 0.99 | 1.19 | 1.47 |
| 28 m/s (101 km/h) | 0.95 | 1.15 | 1.38 | 1.70 |
| 30 m/s (108 km/h) | 1.09 | 1.32 | 1.58 | 1.95 |
| 33 m/s (119 km/h) | 1.31 | 1.60 | 1.91 | 2.36 |
1 kN/m² ≈ 20.9 psf. Other terrains change the figures a lot: use the calculator, which takes terrain 0 to IV.
What this page does not do
- It does not know where you are. You supply the basic wind speed from the map in your National Annex or from the ASCE hazard tool. Getting that number wrong makes everything below it wrong.
- Flat ground only. The orography factor co is 1.0. On a hill, an escarpment or a cliff edge it is larger, sometimes much larger.
- Rectangular buildings, vertical walls. No roofs, canopies, free-standing walls, parapets or curved surfaces.
- No seasonal or directional reduction: cdir and cseason are both 1.0, which is the safe side.
- ASCE side: buildings up to 60 ft, enclosed, Kzt = 1. Partially enclosed and open buildings use different internal coefficients.
Worked example you can check by hand
vb,0 = 27 m/s, terrain II, z = 10 m, zone A, cpi unknown.
Questions people ask
- How do you calculate wind pressure?
- Start from the dynamic pressure of the wind, ½ · ρ · v², with ρ = 1.25 kg/m³ for air. Eurocode EN 1991-1-4 then raises it for height, terrain and gusts to the peak velocity pressure q_p, and multiplies by the pressure coefficients of the zone of the building. For 27 m/s at 10 m in open country (terrain II), q_p = 1.07 kN/m².
- What is the wind pressure at 100 km/h?
- The dynamic pressure of a steady 100 km/h (27.8 m/s) wind is ½ × 1.25 × 27.8² = 482 Pa, about 10.1 psf. On a building, gusts, height and the pressure coefficients make the design figure larger.
- How do you convert wind speed to pressure?
- Pressure in pascals = 0.613 × v², with v in m/s (½ × 1.25 kg/m³). Doubling the speed multiplies the pressure by four.
- What is peak velocity pressure?
- The pressure of the wind at the height of the building including gusts, q_p in EN 1991-1-4: (1 + 7 · I_v) · ½ · ρ · v_m², where v_m is the mean wind at that height and I_v the turbulence. The pressure on a pane is q_p times the difference of the external and internal coefficients.