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Steel workshop buildings

A steel portal frame is the usual way to build a workshop, garage or light-industrial unit in the UK. It gives a clear floor with no internal columns, takes large doors easily and goes up quickly once the slab is down.

Typical workshop sizes

Frames are usually spaced 4.5 to 7.5 m apart. Allow at least 0.5 m between the top of your tallest door and the eaves, because the haunch at each frame and the door's roll box take up that space.

Doors and openings

• Roller shutter doors sized for the largest vehicle plus about 0.5 m each side and 0.3 m above. Powered doors must meet BS EN 13241 and have safety edges or photocells to BS EN 12453.
• Sliding doors or open bays where the building doesn't need to be heated or secure.
• Personnel doors on each escape route. In a heated building, insulated steel doors are needed to meet Part L.
• Windows and rooflights for daylight. Rooflights at about 10% of the roof area give good daylight without too much heat loss.

Mezzanines and offices

A mezzanine floor at about 3 m gives office or storage space without a bigger footprint. It needs its own steelwork, a stair with handrails, and in most cases an escape route that meets Approved Document B.

Heated workshops and Part L

If the workshop will be heated, Approved Document L sets limiting U-values. Under the 2021 edition these are walls 0.26, roofs 0.18, floors 0.18, windows 1.6 and vehicle doors 1.3 W/m²K, with an air-tightness limit of 8 m³/(h·m²). Insulated composite panels (about 100 mm on walls and 120 mm on the roof) normally meet these. The Future Buildings Standard (Approved Document L 2026) applies to work after 24 March 2027.

Fire escape

Approved Document B limits how far anyone has to walk to an exit. For industrial use that is 25 m where there is only one way out and 45 m where there are alternatives. A long workshop usually needs a personnel door at each end.