What is the basic wind velocity vb in Eurocode 1?

The basic wind velocity vb is the characteristic 10-minute mean wind speed at 10 m height over open terrain (terrain category II) with a 50-year return period. It is usually given in the National Annex as vb,0 and may be modified by direction and season factors: vb = cdir × cseason × vb,0.

How do I get the external pressure coefficient cpe?

The external pressure coefficient cpe depends on the building shape, roof type, wind direction and the considered surface zone. Values are provided in tables and figures in EN 1991-1-4 and the National Annex. This calculator lets you input cpe directly so you can use the appropriate value from the code.

Does this calculator replace the Eurocode or National Annex?

No. The calculator is a helper tool that implements the main Eurocode 1 wind load formulas, but it does not replace the official standard or National Annex. You must always verify parameters such as basic wind velocity, terrain categories, pressure coefficients and safety factors against the applicable codes in your country.

Eurocode 1 Wind Load Calculator (EN 1991-1-4)

Q: What does Eurocode 1 EN 1991-1-4 cover?

Eurocode 1 EN 1991-1-4 covers wind actions on structures in Europe. It provides rules to determine basic wind velocity, peak velocity pressure and design wind pressures on buildings and civil engineering works, including factors for terrain, height, orography and structural dynamics.

Compute basic wind velocity, peak velocity pressure and design wind pressure on walls and roofs according to Eurocode 1 EN 1991-1-4.

Wind Load Calculator

1. Site & basic wind

Basic wind velocity v_b,0 (m/s)

National Annex value (10 m height, terrain II, 50-year return).

Direction factor c_dir

Season factor c_season

Terrain category

Used to approximate roughness factor c_r(z).

Orography factor c_o(z)

= 1.0 for flat terrain; > 1.0 for hills, escarpments.

Reference height z (m)

Air density ρ (kg/m³)

Eurocode default ρ = 1.25 kg/m³.

2. Structural parameters

Exposure factor c_e(z)

Includes turbulence and dynamic effects. Use 1.0 if unknown.

Structural factor c_scd

Often 1.0 for low-rise rigid buildings.

c_pe windward

c_pe leeward

Internal coeff. c_pi

Use ±0.2 or ±0.3 as per EN 1991-1-4 if needed.

Loaded area A (m²)

Used to estimate total force F = w × A.

Results

Basic wind velocity v_b: – m/s

Roughness factor c_r(z): –

Mean wind velocity v_m(z): – m/s

Peak velocity pressure q_p(z): – kN/m²

External pressure w_e,wind: – kN/m²

External pressure w_e,lee: – kN/m²

Internal pressure w_i: – kN/m²

Resultant design pressure w_net,wind: – kN/m²

Resultant design pressure w_net,lee: – kN/m²

Total force F_wind: – kN

Total force F_lee: – kN

Note: Results are characteristic values according to EN 1991-1-4. Apply partial factors and combinations per EN 1990 and National Annex.

How this Eurocode 1 wind load calculator works

This tool follows the main procedure of EN 1991-1-4:2005 (Eurocode 1 – Actions on structures – Part 1‑4: General actions – Wind actions) to estimate wind actions on buildings. It focuses on low‑rise buildings and simple structures and lets you plug in the National Annex parameters (basic wind velocity, pressure coefficients, factors).

1. Basic wind velocity v_b

The basic wind velocity is defined in EN 1991‑1‑4 §4.2 as the 10‑minute mean wind speed at 10 m height over terrain category II with a 50‑year return period:

v_b = c_dir · c_season · v_b,0

v_b,0 – fundamental value from the National Annex (m/s).
c_dir – directional factor (often 1.0 if not specified).
c_season – season factor (1.0 for year‑round use).

2. Mean wind velocity v_m(z)

The mean wind velocity at height z is:

v_m(z) = c_r(z) · c_o(z) · v_b

The roughness factor c_r(z) depends on terrain category and height. The code gives a logarithmic expression. To keep the calculator practical and transparent, we use a simplified power‑law approximation:

c_r(z) ≈ (z / z_ref)^α

with z_ref = 10 m and α depending on terrain:

Terrain I: α ≈ 0.10
Terrain II: α ≈ 0.16
Terrain III: α ≈ 0.22
Terrain IV: α ≈ 0.28

The orography factor c_o(z) accounts for hills and escarpments and is usually 1.0 for flat terrain.

3. Peak velocity pressure q_p(z)

The peak velocity pressure at height z is given by EN 1991‑1‑4 §4.5:

q_p(z) = 0.5 · ρ · v_m(z)² · c_e(z)

ρ – air density (default 1.25 kg/m³).
c_e(z) – exposure factor including turbulence and dynamic response.

The calculator outputs q_p(z) in kN/m² (1 kN/m² = 1 kPa).

4. External and internal pressure

The design external wind pressure on a surface is:

w_e = q_p(z) · c_pe · c_scd

The internal pressure is:

w_i = q_p(z) · c_pi

The resultant net pressure on a wall or roof is then:

w_net = w_e + w_i

The calculator lets you specify different external coefficients for windward and leeward faces and an internal coefficient. It then reports:

w_e,wind, w_e,lee – external pressures on windward and leeward faces.
w_i – internal pressure (same magnitude for both faces).
w_net,wind, w_net,lee – net design pressures.
F_wind, F_lee – total forces on the specified area A.

5. Choosing c_pe and c_pi

External pressure coefficients c_pe and internal coefficients c_pi must be taken from EN 1991‑1‑4 and the National Annex. Typical values for low‑rise rectangular buildings are:

Windward wall: c_pe ≈ +0.8
Leeward wall: c_pe ≈ −0.3 to −0.5
Side walls: c_pe ≈ −0.5 to −0.7
Internal: c_pi ≈ ±0.2 or ±0.3 depending on openings

Always verify the correct coefficients for your geometry, roof pitch, and wind direction in the code.

Step‑by‑step Eurocode 1 wind load example

Suppose you have a 10 m high industrial hall in terrain category II with basic wind velocity v_b,0 = 24 m/s, c_dir = 1.0, c_season = 1.0, and you want the wind pressure at roof height.

Set v_b,0 = 24 m/s, c_dir = 1.0, c_season = 1.0 → v_b = 24 m/s.
Select terrain II, z = 10 m → c_r(10) ≈ 1.0, c_o(z) = 1.0 → v_m(10) ≈ 24 m/s.
Use ρ = 1.25 kg/m³, c_e(z) = 1.0 → q_p(10) = 0.5 · 1.25 · 24² ≈ 360 N/m² = 0.36 kN/m².
Take c_pe = +0.8 (windward wall), c_pi = 0.0, c_scd = 1.0:

w_e = 0.36 · 0.8 ≈ 0.29 kN/m²

w_net = 0.29 kN/m² (no internal pressure)

If the loaded area is A = 50 m², the total force is F ≈ 0.29 × 50 ≈ 14.5 kN.

Limitations and good practice

This tool is intended for preliminary design and education, not as a substitute for a full code check.
For tall, flexible or dynamically sensitive structures, you must follow the full dynamic procedure in EN 1991‑1‑4.
Always use the National Annex for your country for v_b,0, terrain parameters, and pressure coefficients.
Combine wind actions with other loads using EN 1990 and apply appropriate partial factors γ_Q.

Eurocode 1 wind load – FAQ

What does Eurocode 1 EN 1991-1-4 cover?

EN 1991‑1‑4 specifies how to determine wind actions on buildings and civil engineering works in Europe. It defines basic wind velocity, terrain categories, roughness and orography factors, peak velocity pressure, external and internal pressure coefficients, and dynamic response for flexible structures.

Can I use this calculator for any European country?

The formulas are generic Eurocode 1, but each country publishes a National Annex with its own basic wind map, factors and sometimes modified coefficients. You can use this calculator if you input the correct National Annex values, but you must always verify them against the official documents.

Does the calculator include dynamic wind effects?

Dynamic effects are represented in a simplified way through the exposure factor c_e(z) and structural factor c_scd. For low‑rise, stiff buildings, these are often taken as 1.0. For tall or slender structures, you should perform a full dynamic analysis as described in EN 1991‑1‑4 and possibly wind tunnel testing.