Short answer: for a typical 4m × 3m patio with a Colorbond roof, 75×75×4mm SHS posts and 100×50×4mm RHS beams is a common starting point on the Gold Coast. Bigger spans, heavier roofs, or cyclonic wind zones push those sizes up, so this is a guide — not engineering. Council and your insurer will want an engineer's certificate for anything attached to the house.
The three numbers that decide it
Patio sizing comes down to three things: the span (post to post), the roof load on top, and the wind region. The Gold Coast sits in wind region B, which is more demanding than inland Brisbane. Coastal Currumbin and Tugun blocks get extra wind pressure again, and that flows straight back into your steel sizes.
If you're attaching to an existing house, you also need to think about how the beam ties into the fascia or wall — that's where most DIY patio jobs come unstuck, not the steel itself.
Typical starting sizes by span
| Span (post to post) | Common post (SHS) | Common beam (RHS) |
|---|---|---|
| Up to 3.0m | 75×75×4.0mm | 100×50×4.0mm |
| 3.0m – 4.0m | 75×75×4.0mm | 150×50×4.0mm |
| 4.0m – 5.0m | 89×89×5.0mm | 150×50×5.0mm |
| 5.0m – 6.0m+ | 100×100×5.0mm | 200×100×5.0mm (or UB) |
Finish: painted, DuraGal or hot-dip galvanised?
Painted black steel is the cheapest, but you'll need to prime and topcoat every face — including the cut ends — and re-do it every few years. DuraGal is the workhorse for Gold Coast patios: a pre-galvanised finish that paints up cleanly. Within a few kilometres of the beach or for jobs you never want to touch again, hot-dip galvanised is worth the extra. We arrange dipping through our local galvaniser as part of the fab job.
Posts: footings matter as much as the steel
An undersized footing will fail before an undersized post will. As a rough rule, a 75×75 SHS post wants at least a 450mm × 450mm × 600mm deep concrete pad in firm Gold Coast soil. Reactive clay (lots of Burleigh and Robina) usually wants more. Drop in to the yard with your site sketch and we'll talk you through it.
What we typically supply
- SHS posts cut to length in DuraGal or hot-dip galvanised finish
- RHS beams in 6.0m and 7.5m standard, or cut to your spec
- Base plates and cleats fabricated to your drawing
- Crane-truck delivery if you've got long beams or no lifting gear on site
Send us your patio plan — a sketch on the back of a fence palings invoice is fine — and we'll quote you the steel, fabrication and delivery in one hit.
See our structural sections or send a sketch through the fabrication service.
