A clear-span building has no posts or columns inside. The roof is carried by steel frames that span from one wall to the other, so the whole floor is yours to use. It’s the single biggest difference between a modern steel building and a traditional pole shed, and it’s what Steelspan builds every day, with clear spans of up to 30 m.
How a portal frame works #
Each frame is a pair of columns joined to a pair of rafters. The joints at the eaves (the “knees”) and at the peak are rigid, so the frame resists wind and earthquake loads by bending, rather than leaning on posts in the middle. Bracing in some of the wall and roof bays then keeps the building stable along its length.
Steelspan frames are cold-formed Z275 galvanised steel with bolted knee connections. Our clear-span portals don’t use internal knee braces or apex braces, the diagonal members you see in the corners of many sheds, so you keep more usable height near the walls.
Where clear span pays off #
- Machinery and vehicles. Tractors, trucks and loaders can turn inside without a post in the way, and there’s nothing to back into.
- Warehouses and workshops. Racking, production lines and forklift aisles can go wherever the work needs them, and can move later.
- Storage and hay. Stacks go wall to wall, and loaders work freely.
- Arenas, courts and community spaces. Open floor is the whole point.
- Changing use. A clear floor is easy to repurpose, which helps resale value.
Think about the future too. A fruit packhouse might have conveyor belts and sorting tables laid out around its columns today. When the owner later wants to improve the layout or bring in new equipment, those columns can be in exactly the wrong place, and they’re very hard to remove once the building is up. Clear span keeps your options open.
The trade-offs #
Wider spans need deeper, heavier frames and bigger footings at the columns, so cost per square metre rises with span. For a very wide building, or one carrying a heavy mezzanine, a line of internal columns can be cheaper. A good designer will show you both options and the price difference, then let you choose.
Clear span vs a pole shed #
Pole sheds use timber poles set in the ground, and the roof span between poles is usually limited, so wider pole sheds have poles inside. That isn’t wrong, and for some uses it’s fine. But if you’re paying for floor space, you probably want to use all of it. Our steel vs timber post goes into the detail.
How wide can you go? #
With our cold-formed Z275 galvanised system, we can typically go clear span to about 20 m on most sites, and sometimes further. Beyond that, a truss-style frame can take spans up to 30 m. Where it suits the job better, we’ll recommend a hot-rolled system, such as welded steel I-beam frames, for spans of 30 m and above, and we’ll tell you when that applies.
We can also build a hybrid building, with our cold-formed system on timber poles, if that’s what you want, though it isn’t common for us.
Every frame is engineered for the site’s wind, snow and earthquake loads, so the same span might use a different frame on an exposed coastal hill than in a sheltered spot.
Talk to Steelspan #
Tell us what needs to move around inside the building, and we’ll design a frame that keeps the floor clear. Start with our Easy Shed Quote or call 0800 787 726.
