Steel carports
A carport looks simple: four posts and a roof. Yet it is exactly where people economise on what cannot be put right later — on the depth of the footing, the section of the post and the fall of the roof. Here it is taken apart joint by joint, in the order the shop actually works through it.
The carport as a whole
A mono-pitch carport for one car is two front posts and two rear ones, a load-bearing member along the front edge, purlins across it and roofing on top. The load travels downwards: snow lands on the roofing, the roofing passes it to the purlins, the purlins to the truss, the truss to the posts, the posts to the foundation. The weakest link in that chain sizes the whole structure, and it is rarely the part people look at.
Those dimensions are not about looks. A width of 3.0–3.5 m is the car plus an open door; 5–6 m of length is the car plus room to walk round the front; 2.3 m of clear height is a car with a roof box. For two cars you do not build a wider carport — you add a third frame or a longer-span truss.
Posts: six options
The section is chosen by span and snow load. Warsaw design snow is 0.9 kPa, roughly 90 kg on every square metre of roof, which on a 3×6 m carport adds up to nearly two tonnes. An 80×80×3 tube carries a span of up to three metres with light roofing; beyond that it is 100×100×4.
Two of these six solve space rather than strength. A wall-mounted cantilever removes the front posts altogether: the carport hangs off the house and there is nothing to catch a car door on. A lattice post earns its place where the height is large and the weight must stay down — it is a truss stood on end.
How the post holds on to the ground
This is the most expensive joint to correct: redoing it after erection means dismantling the carport. The choice follows what is already on site.
- Concreted into the ground — cheapest on material, but below the frost line and with a week of waiting.
- Screw pile — no concrete and no waiting, and it takes heaving in its stride; set in a day.
- Base plate on anchors — when the slab is already poured. It has to be a real slab, 150 mm and up, not a levelling screed.
- Adjustable base — for a sloping yard: the height is set on site and grout goes underneath.
The top: beam or truss
Up to four metres of span there is nothing to argue about — a profile beam is simpler and cheaper to make. Beyond that the truss starts to win: at the same span it weighs half as much, so the posts under it get lighter too. You pay for that in joints, and every joint is cutting, fitting and welding.
A triangular truss sets the pitch itself, so it needs no posts of differing height. A parallel-chord truss keeps the underside flat, which matters when the soffit is visible from below and a clean line is wanted. The arched one is for polycarbonate: the sheet bends to a curve and hates a crease.
Roof shape
The cantilever carport stands apart from the rest: both posts move to the back, and nothing is left in front of the car to catch a door on. You pay for that in steel, because a cantilever works in bending and the section grows. The flat-with-a-fall version belongs where the carport meets the house and must not argue with its roof; a parapet runs along the edge and the water goes into a downpipe.
Reinforcement: what to add when it moves
A carport that shifts in the wind almost never bends in mid-span — it is the connection that moves. So the reinforcement goes into the joint.
Sometimes the cheap answer is not a gusset but an extra millimetre of wall: 100×100×3 and 100×100×4 differ in price by less than a dozen gussets cost once cutting and grinding are counted. That sum is worth doing before the cutting list, not after.
Where to go next
If the carport is fixed to the house and has to cover the entrance, see door canopies: the same question of anchoring into a wall, but with the load arriving at two points. If it later gets clad with walls it becomes a garage, and ventilation has to be thought about in advance. Price, lead time, coating and fixings are in how ordering works.
Frequently asked questions
What does a single-car carport cost?
The price is built from six parts: steel is about a third, then cutting and bending, welding and assembly, coating, installation and delivery. That is why tube you buy yourself hardly moves the quotation — it only changes the first third. The breakdown is in how ordering works.
Can a carport be built without concrete?
Yes, on screw piles. They work the moment they are wound in, need no week of curing and cope better with soil that heaves. Concreting into the ground is still cheaper on material, but it means waiting and getting below the frost line — in Warsaw that is 0.9–1.2 m.
What fall does a carport need?
No less than 3°, and in practice 3–5°. A shallower fall looks level to the eye, but water and dirt stay on the roof, and in winter ice joins them. The fall comes either from the truss itself or from front and rear posts of different heights.
Polycarbonate or profiled sheet?
Polycarbonate lets light through and bends to a curve, so it goes on arched and half-arch carports. Profiled sheet is cheaper, stiffer and does not yellow, but it is dark underneath and noisier in rain. For one car sheet is the usual answer; against a house with windows onto the yard, polycarbonate.
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