TECHNICAL · EN 12424 WIND LOAD CLASSIFICATION
A consultant has put a class in a document and you need to know what it commits you to. EN 12424 grades a door by the pressure it withstands across the leaf, tested as a complete assembly. It is the number one technical objection in hangar-door buying, and on an opening over 20 m it is the difference between a door and a hole in the building.
A class is a test result. The door is built as it will be delivered — same fabric, same guides, same fixings — and loaded with air pressure across the leaf until the class pressure is reached. It has to stay in its guides, stay operable and deflect no more than the standard permits. The class is the pressure it held, not the wind it will meet.
Two consequences follow, and both matter more than the number itself. A class belongs to a tested assembly, so changing the fabric, the guide section or the fixing centres invalidates it. And a class says nothing about the building: the structure that receives the guide-column reactions is checked separately, by whoever is responsible for the frame.
„Class 4 is enough — we are not on the coast.”
An open airfield 60 km inland can demand the same class as a quayside hall, because terrain roughness and the height of the leaf drive the gust pressure as hard as distance from the sea does. Sheltered means screened upwind of this opening — not somewhere in the region.
| Class | Test pressure | Beaufort equivalent | Typical siting |
|---|---|---|---|
| Class 1 | 300 Pa | Bf 7 | Sheltered inland sites, screened on the windward side |
| Class 2 | 450 Pa | Bf 8 | Inland industrial parks with surrounding built form |
| Class 3 | 700 Pa | Bf 9 | Open inland terrain, airfields away from the coast |
| Class 4 | 1 000 Pa | Bf 10 | Exposed inland sites, hilltops, large open aprons |
| Class 5 | > 1 000 Pa | Bf 11 | Coastal sites, naval bases, shipyards, exposed airfields |
Beaufort equivalents are indicative only: they convert a mean wind speed, while the class is a static pressure across the whole leaf. Use them to explain the class to a building owner, never to specify one.
The class follows the ground the building stands on. A plant with a head office inland and a hall on the quay is a coastal building. Basic wind velocity comes from the national annex to EN 1991-1-4, per country and per region.
Roughness is directional. A hall screened by forest to the east and open to the sea to the west takes the western case, and the door faces it.
Gust pressure rises with height. On a 15 m leaf the head of the door sees materially more pressure than the sill, which is why the leaf, the guides and the header are calculated as one assembly.
The class is a test result on a door, not a verdict on your opening. The last step is checking that the structure behind the guide columns can take the reaction the door will hand it.
| Category | Description | What it means for the door |
|---|---|---|
| 0 | Sea or coastal, exposed to open sea | Highest gust pressure. Naval yards, quayside halls, island air bases. |
| I | Lakes, flat land with negligible vegetation | Typical of runway-side hangars and dispersal aprons. |
| II | Low vegetation, isolated obstacles | Most inland industrial sites sit here. |
| III | Villages, suburban or permanent forest | Screening reduces the gust — but only if it is upwind of the opening. |
| IV | Urban, at least 15 % covered by buildings over 15 m | Rare for large-span halls; usually a retrofit into a city plant. |
Terrain category 0, leaf head at 15.2 m, gust from the open sea with no upwind screening. The pressure at the head of the leaf governs the whole assembly, so the class is taken from the worst case on the elevation — not from an average across the opening.
Classification is only useful if it is traceable. Each door leaves with the classification it was quoted against, the report it derives from, and the reactions the building has to carry. Where a figure below is dotted, we have not yet released it — a blank is better than a class we cannot evidence.
The leaf transfers wind load into the guide profile through the keder and roller line. Rail section and fixing centres are set by the calculated load, not by the door width.
Positive engagement between leaf and guide at intervals up the opening, so a gust cannot peel the fabric out of the rail.
Define what happens at the limits — including the failure position when power is lost mid-travel.
Issued as a calculation note with the offer, so the building engineer can check the structure that receives them.
Give us the site and the opening and we come back with the governing class, the reactions your structure has to carry, and a price — usually within three working days.
Nothing on this page is a substitute for a calculation to EN 1991-1-4 for your building. It is here so that the number in your specification stops being a guess.
