Not all steel sheds are built the same way, and that’s by design. The frame inside your shed’s walls does the structural heavy lifting, and different frame types are engineered for different jobs. The Australian shed market is dominated by two primary structural approaches: the lighter-weight C–purlin shed design and the more heavy-duty Rectangular Hollow Section (RHS) steel frame. Understanding the difference between both steel framing options means you end up with a shed that’s actually built for what you’re using it for.
Here’s how the two compare, and where each one shines.
The Mechanics of C Purlin Shed Design
A C-purlin shed relies on cold-formed steel. This means flat sheets of thin-gauge steel (typically between 1mm and 3mm) are folded into an open ‘C’ shape (often called a C channel or C-section).
The biggest advantage of a C-purlin framework is cost and weight. Because the steel is thinner and open-backed, it requires less raw material, making it cheaper to manufacture and transport. C-purlin suits single and double garages, hobby studios, and small workshops — spaces where you’re protecting vehicles, tools or a lawnmower rather than clear-spanning heavy machinery – and is a cost-effective option if you’re the handy type and are looking for a supply-only kit that you can install (or manage) yourself.
It’s a smart, efficient choice for a huge range of sheds. Because the profile is open rather than a closed tube, engineers typically add internal knee and apex bracing to manage torsional load. It’s worth factoring in if you need maximum clear internal space, but not a problem for smaller-footprint builds.
The Strength of RHS Steel Frame Sheds
In contrast, Rectangular Hollow Section (RHS) entails hot-rolled structural steel formed into a completely closed, four-sided tube. The wall thicknesses are generally much heavier (often 2mm to 6mm+).
Because it is a closed loop, an RHS frame refuses to twist; it is inherently rigid. This immense strength-to-weight ratio allows for massive “clear-span” designs. With an engineered shed frame built from RHS portal frames, you can bridge much wider gaps without requiring intrusive internal knee bracing. For agricultural machinery, industrial workshops, and vast open spaces, RHS is the go-to choice.
RHS is the natural fit for farm sheds, machinery and equipment storage, hay sheds, dairy sheds, and industrial workshops: anywhere you need wide clear-span space and the frame needs to shrug off potential knocks from heavy vehicles and gear.
Head-to-Head Comparison: Shed Purlins vs. Structural RHS
| Structural Feature | C Purlin Frame | RHS Steel Frame |
| Steel form | Cold-rolled, open C channel profile. | Hot-rolled, closed, 4-sided tube. |
| Typical gauge | 1-3mm | 2-6mm+ |
| Best for | Garages, studios, small workshops | Farm sheds, machinery, hay/dairy sheds, industrial |
| Clear-span capability | Good, with bracing | Excellent, minimal bracing. |
| Made & engineered | Australian-made, Australian standard | Australian-made, Australian standard |
| Impact tolerance | Moderate | High |
Why the Framework Dictates Your Shed’s Ideal Usage
For lighter applications, a well-engineered C-purlin frame will comfortably meet its wind rating and stand strong for years. But for buildings under constant heavy use (wide spans, vehicle movement, exposed rural sites), RHS’s rigidity means less long-term movement in the frame, which translates to less strain on cladding and fasteners over decades of use.
If you’re building a garage, studio or small workshop, a C-purlin frame gives you everything you need without paying for capacity you’ll never use. But if you’re storing hundreds of thousands of dollars’ worth of farm machinery, operating heavy vehicle hoists, or building a premium workspace, choosing the heavy-duty RHS steel for your shed will make all the difference in the long-term.
Making the Right Choice for Your Property
At CV Sheds, we build for longevity; it’s why our motto is ‘Built for Generations.’ Whether your project calls for the efficiency of C-purlin or the clear-span strength of RHS, every frame we build is Australian-made and engineered for the conditions it’ll actually face.
Not sure which frame suits your project? Contact our sales team and we’ll help you build it right, from the ground up.