Steel garages and sheds
A steel garage goes up in a few days, which is exactly why the ventilation gets forgotten. A vent under the eaves costs pennies, and its absence rusts the garage from the inside faster than the rain does from outside.
Frame and cladding
The frame is posts at the corners and along the walls, a top rail round the perimeter and purlins under the roof. The cladding is not load-bearing: it closes the box and holds its shape, but the snow load on the roof is taken by the purlins and the top rail.
The roof falls away from the door: otherwise the water off the roof lands exactly where the door opens. A gap is left between the bottom of the cladding and the slab so that the sheet does not stand in water.
Six variants
- Frame with profiled sheet — the cheapest and the quickest; cold.
- Sandwich panels — a warm garage with no separate insulation and no condensation on the ceiling.
- Single-car lock-up — for one car, set down on a slab and moved in one piece.
- Shed with a window — workshop, tools, firewood; the window goes on the north side so it does not cook in summer.
- Attached to the house — one wall is already there and the saving is real; you will need a flashed abutment and drainage.
- Garage with a carport — a second car under a roof, without walls or a door.
Insulation and condensation
Condensation settles where warm air meets cold steel. Hence a rule that runs against intuition: covering the steel matters more than insulating it. Five centimetres of polystyrene glued to the sheet with no gaps works better than ten centimetres of mineral wool laid with voids at the edges.
If the garage is unheated, insulating it makes no sense at all — what it needs is a ventilated cavity. It does not heat, it dries: air passes behind the cladding and carries the moisture away, and the steel stays dry. The detailed wall sections are in how ordering works.
Where to go next
The door is a conversation of its own: sectional doors need headroom above the opening, roller shutters save space, swing doors are the cheapest. All of it is in gates and wickets. If the building outgrows garage sizes and the span passes six metres, see halls and frames.
Frequently asked questions
Why is the roof of a steel garage wet?
That is condensation. Warm damp air from the car and from the ground meets the cold steel of the roof and the water settles on it as dew. Insulation helps only if it covers the steel completely and has a vapour barrier; without vents under the eaves even an insulated garage will sweat.
Does a garage need a foundation?
Not always. A bolted, non-permanent garage sits on an existing slab or strip footing and can be taken apart and moved. The moment a full foundation appears it becomes a permanent structure, with all the paperwork that follows.
Profiled sheet or sandwich panel?
Sheet is cheaper and quicker, but it is a cold box. A 50 mm sandwich panel gives a warm garage with no separate insulation and no condensation on the ceiling, but costs noticeably more and needs a more accurate frame.
What size should I build?
3.5 m wide and 2.4 m clear height — a car with its door open and a roof box on top. For length take 6 m: the car plus a metre for a bench or shelves against the back wall.
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