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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.

Site

Fundamental basic wind velocity v_b,0 (m/s)

From the wind map in your National Annex — 10-minute mean, 10 m above ground, terrain II, 50-year return. In Spain (CTE DB SE-AE) it is 26 m/s in zone A, 27 in zone B and 29 in zone C. Look yours up; do not guess.

Terrain category

Height of the pane above ground z (m)

For a facade, use the height of the top of the building when the building is not tall — Eurocode lets the whole face be checked at the reference height.

Where the pane sits

Zone on the facade

If in doubt, leave it on A: it is the most demanding and it is where the glass actually breaks.

Building shape h/d

Height divided by the depth in the wind direction. Only changes zones D and E.

Internal pressure c_pi

—

Suction (outward)

— kN/m²

Pressure (inward)

— kN/m²

Peak velocity pressure q_p

— kN/m²

Governing value

— kN/m²

use this for the glass

Eurocode EN 1991-1-4, step by step

q_b = ½ · ρ · v_b² // ρ = 1.25 kg/m³, v_b = c_dir·c_season·v_b,0, both taken as 1.0 k_r = 0.19 · (z₀ / 0.05)^0.07 // terrain factor c_r(z)= k_r · ln(z / z₀) // roughness, floored at z_min v_m = c_r · c_o · v_b // c_o = 1.0, flat ground I_v = 1 / (c_o · ln(z / z₀)) // turbulence intensity q_p = (1 + 7·I_v) · ½ · ρ · v_m² // peak velocity pressure w = q_p · (c_pe − c_pi) // net pressure on the pane

Terrain	z₀ (m)	z_min (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, c_pe,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 c_pe,10 values are for whole structural elements and would under-read here.

Zone	A	B	C	D	E
c_pe,1, h/d ≥ 5	−1.4	−1.1	−0.5	+1.0	−0.7
c_pe,1, h/d = 1	−1.4	−1.1	−0.5	+1.0	−0.5
c_pe,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 c_pi = +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, γ_Q = 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

K_z = 2.01 · (z/z_g)^(2/α) // z floored at 15 ft q_h = 0.00256 · K_z · K_zt · K_d · V² // psf; K_zt = 1.0, K_d = 0.85 p = q_h · (GC_p − GC_pi) // GC_pi = ±0.18, enclosed building exposure B: α = 7.0, z_g = 1200 ft exposure C: α = 9.5, z_g = 900 ft exposure D: α = 11.5, z_g = 700 ft

GC_p 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.

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 c_o 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: c_dir and c_season are both 1.0, which is the safe side.
ASCE side: buildings up to 60 ft, enclosed, K_zt = 1. Partially enclosed and open buildings use different internal coefficients.

Worked example you can check by hand

v_b,0 = 27 m/s, terrain II, z = 10 m, zone A, c_pi unknown.

q_b = ½ · 1.25 · 27² = 0.4556 kN/m² k_r = 0.19 · (0.05/0.05)^0.07 = 0.1900 c_r = 0.19 · ln(10/0.05) = 1.0067 v_m = 1.0067 · 27 = 27.180 m/s I_v = 1 / ln(10/0.05) = 0.18874 q_p = (1 + 7·0.18874) · ½ · 1.25 · 27.180² = 2.32119 · 0.46172 = 1.0717 kN/m² suction = 1.0717 · (−1.4 − 0.2) = −1.715 kN/m² characteristic × 1.5 = −2.572 kN/m² design

Read this. This is a pre-dimensioning aid for people who already know the subject. It is not a structural calculation and it does not replace the standard, your National Annex or the engineer who signs the job. The basic wind speed and the orography are yours to get right.