Choosing the right steel frame for your shed will not only impact the price of the build but will play a role in how well it works for your intended purpose. Understanding the difference between an RHS vs a C-section can save you thousands in repairs, replacement costs, or regret down the track. 

Whether you’re building a machinery shed, horse arena, or farm workshop, the steel you choose determines how long it’ll last and what it can handle.

Key Insights

  • C-section (purlin) frames: More affordable upfront but made from lighter-gauge steel (around 1 mm thick). They are more prone to flexing under load.
  • RHS (Rectangular Hollow Section): A hot-rolled structural steel section (typically 2–6 mm thick). Its thicker walls allow for welding and full prefabrication in the factory before delivery, resulting in significantly greater strength and rigidity.
  • UB (Universal Beam / I-Beam): Heaviest-duty option for industrial buildings and very large spans (50m+).

What Is C-Section Steel?

C-section steel gets its name from its shape – a three-sided channel that looks like the letter ‘C’. It’s cold-rolled from flat sheet steel, typically between 1mm and 3mm thick.

In C-section framed sheds, these purlins form the main portal frames and are bolted together on site, similar to assembling a Meccano set. This makes them cheaper and quicker to manufacture.

The trade-off? That open C-shape can flex, twist, and bend under stress. If you’ve got machinery moving around your shed (tractors, forklifts, or trucks), an accidental bump to a C-section column can compromise the entire structure. They’re also limited to about 12 metres in span before needing significant extra bracing that eats into your usable space.

What Is RHS and UB Structural Steel?

RHS (Rectangular Hollow Section) is a fully enclosed, four-sided steel column, essentially a thick-walled tube. It’s hot-rolled at high temperatures, producing steel that’s 2mm to 6mm thick. That closed profile gives RHS dramatically more strength than open C-section purlins of similar dimensions.

UB (Universal Beam), also known as an I-beam or H-beam, elevates structural steel to the next level. These are the heavy-duty I-shaped sections you’ll see in commercial and industrial buildings. UBs are manufactured to Australian Standard AS3679/300 and can span over 50 metres wide with heights exceeding 9 metres.

Both RHS and UB frames are typically welded together in a factory with heavy-duty connection plates, then bolted on site. This creates rigid, permanent joints rather than the bolt-together brackets used in C-section sheds, which can allow movement over time.

The Real-World RHS vs C-Section Difference

When you compare RHS or UB vs C-section framed sheds, the main difference is in three areas: durability, span capability, and future-proofing.

Durability

RHS and UB structural steel handles impact, wind loading, and daily wear far better. If you’re working around machinery, livestock, or heavy equipment, structural steel won’t dent or buckle from an accidental knock.

Span Capability

Want clear span without columns cluttering your workspace? RHS frames handle larger distances without the knee braces and apex ties that C-section sheds need. UB frames go even further for truly massive structures.

Future-Proofing

Planning to extend your shed later or hang hoists, block-and-tackle, or overhead equipment? Structural steel handles additional loading. C-section frames have limited capacity for add-ons.

Which Frame Type Should You Choose?

For temporary storage, C-section framing can be a suitable option and save you money upfront.

For machinery sheds, workshops, hay storage, or equine arenas, RHS frames deliver the strength and longevity you need. The RHS vs C-section difference becomes obvious the first time you watch a tractor reverse a bit too close to a column – RHS shrugs it off.

For large industrial buildings, aircraft hangars, or commercial warehouses, UB structural steel provides the heavy-duty capability for truly massive spans and loads.

Get the Right Shed for Your Property

Not sure which frame type suits your project? Talk to our team about your requirements. We design and build custom sheds using RHS and UB structural steel, engineered for Australian conditions and built to last decades, and we can help you determine the right materials for your build.