Volex Labs / Calculations / Wind loading to EN 1991-1-4, with the UK National Annex.

Wind loading to EN 1991-1-4, with the UK National Annex.

From postcode-level basic wind speed to the pressure on each face: Volex runs the full EC1-1-4 chain — vb with the directional and season factors, terrain roughness, turbulence intensity, peak velocity pressure qp, and external/internal pressure coefficients for walls and roofs.

The UK National Annex is applied throughout (Table NA.1 and the NA altitude method), and each intermediate value is reported with its equation number so the calculation can be followed against the code — or against Cook's Designers' Guide, which is what the module is validated on.

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What Volex checks

Basic wind velocity vb — §4.2 Eq 4.1 + UK NA Table NA.1
Terrain roughness cr(z) — §4.3.2
Turbulence intensity Iv(z) — §4.4 Eq 4.7
Peak velocity pressure qp(z) — §4.5 Eq 4.8
Pressure coefficients cpe/cpi — §7 + UK NA

Validated against the published example

Peak velocity pressure qp — Terrain Cat II, z = 10 m BS EN 1991-1-4 §4.5 Eq 4.8; Cook 'Designers' Guide'

Quantity	Published	Volex	Error
qp	0.763 kPa	0.7628 kPa	0.03%
Iv	0.189	0.1887	0.14%

This case is one of 359 published checks the platform passes — the full table, with every source and every error, is public at volexlabs.com/verification.

Frequently asked

Does it use the UK National Annex?

Yes — directional/season factors, the UK terrain categories and Table NA.1 are applied, which is where most spreadsheet wind calcs quietly go wrong.

What do I get out?

Every intermediate value — vb, cr(z), Iv(z), qp(z) — with its equation reference, then face pressures from the cpe/cpi coefficients for your geometry.

Is it validated?

Against hand calculations from Cook's Designers' Guide to EN 1991-1-4 — qp within 0.03% on the reference case. The verification page shows all wind cases.

Can I use the result in a frame design?

Yes — wind results feed Volex's load combination and frame modules, or export the pressures to use in your own analysis.

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