Purlins are longitudinal, horizontal bars or beams used for structural support in buildings, primarily in roofs. They also help to increase a building’s resistance to heavy winds and earthquakes. Galvanised steel is commonly used to manufacture purlins as the galvanisation process helps to protect against corrosion and rust. Steel is also popular construction material as it is lightweight, durable, solid and resistant to termites and other pests.
What Is The Difference Between a Purlin and a Rafter?
Purlins and rafters both provide structural support to a building. Rafters are beams angled upwards from the ground and are usually made of wood. They meet at the top of the roof at a ridge beam (the ridge beam usually has extra bracing to attach it to the rafters). Purlins, on the other hand, are large beams perpendicular to the rafters.
Types of Steel Purlins:
There are two different types of purlins:
C Shaped Purlins
As the name suggests, C purlins (pictured below) are manufactured into the shape of the letter C. These sections are primarily used to shape a building’s shell structure wall and floor joists.
Z Shaped Purlins
Z sections are manufactured into the shape of the letter Z. They are built to shape a building’s shell structure’s roof and wall joists. Z purlins are stronger than C purlins due to their overlapping capability.
Purlin Span
The span refers to the distance between the centres of the cleat bolts at each end of the purlin. There are different types of spans, each representing a complete purlin run system.
Single Purlin Span
A single span is supported by bolting the web of the purlin to a cleat or other rigid structure. Under these conditions, bridging does not influence inward capacities, but outward capacities vary depending on the number of rows of bridging.
Double Purlin Span
Double spans are simply supported at each end and in the centre. They comprise of either one purlin over the full length or two purlins lapped together over the central support to provide continuity. Both inward and outward capacities are influenced by bridging in double spans.
Continuous Purlin Span
Continuous spans are simply supported at each end and at a series of equally spaced intermediate supports. For outwards loads on equal continuous spans the bridging shown is required in the end spans. Z purlins are commonly used for these continuous spans.
How Dynamic Steelform Can Help
If you need purlins for your next construction project, Dynamic Steelform is here to help! Our C and Z purlins are made from high-tensile G550 Z350 galvanised steel and come in various sizes and thicknesses. They can be rolled, cut or punched to suit your requirements. To discuss your project requirements please contact us on 08 9434 6888 or visit our facility at 7 Cartwright Dr in Forrestdale, Western Australia, during our business hours.