Standards Library · 01
BS EN 1991-1-4
Wind actions
The Eurocode that governs wind actions on structures. For rooftop solar it is the standard that decides whether an array stays on the roof, and it is applied to the specific site rather than to a national average.
What it is
BS EN 1991-1-4 is the part of Eurocode 1 dealing with wind actions. It is used with the UK National Annex, which carries the nationally determined parameters, including the wind speed map for the United Kingdom.
The standard establishes a peak velocity pressure at the site, derived from a fundamental basic wind velocity, then modified for direction, season, altitude, terrain roughness, distance to shoreline and building height.
Why it matters for rooftop solar
An array raises the surface the wind acts on and changes the way air moves across the roof. The governing case is usually uplift, not added weight — the array is more often at risk of being pulled off than of pressing the roof down.
Site exposure dominates the result. Two identical buildings, one inland and one on an exposed coast, produce materially different wind actions. A figure taken from a national average is not an assessment of that building.
BS EN 1991-1-4 predates widespread rooftop PV and does not itself provide pressure coefficients for array aerodynamics. That gap is filled by BRE Digest 489.