Steel halls and frames
This is where calculated structure begins. A carport or a fence can be built to a standard solution; a frame spanning 18 m cannot — snow, wind and stability all get sized. This article does not replace that calculation. It explains what to discuss with the person doing it.
Frame, bracing and cladding
The frame of a hangar is a row of identical frames at 4–6 m centres, purlins between them, bracing, and cladding on the purlins. The frame takes vertical load and wind across the building; the bracing holds it along.
Bracing costs little and is struck off first: on a drawing it looks like optional thin angle. It is in fact the only thing keeping the frames from going over lengthways — like dominoes, which stand upright only while something holds them.
How the span is covered
- Portal frame — up to 12 m; a clean ceiling with no truss, which matters in a shop with services hung from it.
- Columns with a truss — 12–30 m; at the same span a truss is one and a half to two times lighter than a beam.
- Arched hangar — quick and cheap, but almost no usable height at the walls.
- Light gauge sections — a light bolted frame; almost no welding on site.
- Open canopy hangar — machinery, bulk storage, drying; half the cost of a closed building.
- With a crane beam — the crane hangs on the frame, not on the walls; designed separately.
Cladding and insulation
A cold hangar is clad in profiled sheet on the purlins — enough to keep out weather and wind. A warm one is built from sandwich panels: they carry factory insulation and go up in one layer, with no vapour barrier or battens on site.
The halfway option — "sheet for now, we will insulate later" — is best avoided. Insulating from the inside against cold steel without a proper vapour barrier puts condensation inside the build-up, and it shows a year or two later as rust streaks at the joints.
Where to go next
A smaller building of the same kind, for one or two cars, is a garage or shed: the same questions of cladding and ventilation, without the calculation. The door is chosen to the opening — see gates and wickets. Price, lead time and coating are in how ordering works.
Frequently asked questions
Portal frame or truss?
Up to 12 m the two compete: a portal frame gives a clean ceiling with no truss below it, a truss uses less steel. Beyond 12 m the truss wins almost every time, because its depth can grow without the weight growing, whereas a beam has to grow its whole section.
What is bracing for?
A frame carries load in its own plane, but along the building it carries nothing. Bracing — the cross members between frames — stops the row folding lengthways. It is the first thing struck off a quotation, on the grounds that it "carries nothing", and that is exactly how a collapsed frame line happens.
Can a crane be hung on an existing frame?
Only if the frame was designed for one. Crane beams bear on brackets off the columns, and the whole way the frame works changes: a horizontal load from braking the trolley is added. Adding a crane to a finished frame without recalculation is not on.
Which is cheaper, an arched hangar or a frame?
The arch is cheaper and quicker, but there is little usable height at the walls: you cannot stand racking against them. For storage that is often decisive, so straight frames go under storage and the arch under machinery and drying.
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