When planning a shed project in New Zealand, one detail that’s easy to overlook is the type of purlins used in your design. Purlins form the backbone of your shed’s roof structure, so choosing the right system is crucial for long-term strength, stability, and ease of maintenance.
In this guide, we explain what a purlin is and compare the most common types: Timber purlins, steel purlins, and C-section purlins, so you can make the best choice for your next build.
A purlin is a horizontal beam that supports your roofing iron and helps transfer loads to the main rafters. In simple terms, purlins and rafters work together to hold up the roof, with purlins running parallel to the ridge line.
Whether you’re constructing a farm shed, aircraft hangar, or storage building, the roof purlin plays a vital role in overall performance. Most New Zealand sheds use either timber purlins or steel purlins, each with its own advantages.
Understanding the differences between purlin types and how each contributes to roof strength will help you choose the right system for your structure.
Timber purlins are widely used across New Zealand, particularly in pole sheds and mixed timber-and-steel designs. They’re valued for their natural insulation and acoustic benefits.
For workshops or storage sheds where noise control and warmth are important, timber purlins remain a dependable and proven option.
Steelbone purlins are fully enclosed, V-shaped sections made from high-tensile galvanised steel. They’re designed for strength and durability, commonly used in agricultural and industrial applications.
Steelbone purlins are ideal for wide-bay agricultural sheds that need maximum internal clearance and minimal maintenance.
C-section steel purlins are one of the most common systems used in all-steel and commercial sheds. Available in a variety of profiles and thicknesses, they offer flexibility for different spans.
C-section purlins are best suited to large industrial or commercial buildings, rather than sheds where tidiness or low noise are priorities.
Commonly found in lightweight roll-form sheds, tophat purlins are cost-effective but less robust than enclosed systems.
When comparing timber purlins vs steel purlins, consider the structure’s purpose, environment, and desired finish. For a quiet, insulated workshop, timber purlins are a great fit. For large, open agricultural buildings, steel purlins - particularly enclosed designs - provide superior strength and bird protection.
It’s also worth thinking about installation access, wiring needs, and long-term maintenance. Your purlin choice affects not only strength but also usability and comfort inside the shed.
At Alpine Buildings, we’ve worked with every purlin design system in New Zealand. Our clearspan sheds are engineered to optimise space, performance, and durability - whether that means using pre-dried timber purlins or enclosed steel purlins for extra strength.
If you’re unsure which roof purlin system is right for your project, our team can help you work out what system is best for you.
Start your shed design with Alpine Buildings today and build a structure that lasts a lifetime. Or two.