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How To Support Roof Purlins
At first glance, a roof may look like a relatively straightforward structure — pitched or flat, tiled, or thatched. However, on the inside, it’s a different story. When you strip back what’s inside a roof, there is a complex balancing system of weight and support at play, revolving around one core aspect: purlins. While we’ve covered elsewhere what purlins are exactly, you can keep reading this article to discover exactly how to support purlins in roofs for maximum structural security.
What Are Support Purlins
To those unfamiliar with roofing, purlins often look like rectangular poles or wooden beams in the roof structure, but they are so much more. Not only do they help form the framework that roof tiles lay on (also known as the truss), but they also allow for roofing sheets to be fixed in place securely.
Without correct purlin fixtures, roofs are not as structurally sound, and their coverings won’t be as stable. For example, tiles may come loose, or roof sheets may let water in if the purlin spacing is irregular.
Metal Roof Sheet Purlins
Both the support and the placement of purlins are crucial. If you space out your purlins by too much, the support they offer to the roof won’t be as sufficient and the structural integrity will be weakened overall. On the other hand, if you place your purlins too close together, you’ll be creating extra work for yourself in the form of the overlap and may be wasting materials.
To work out your purlin spaces for metal sheets, you must consider the thickness of the sheet itself as this affects its strength. As a rule of thumb, purlins should never be more than 1.2 metres apart and should always be 50mm wide at least (to allow for the sheets to be fixed to them correctly).
• If using metal roofing sheets with a thickness of 0.7mm, your roof purlins should be no more than 1.2 metres apart.
• If using metal roofing sheets with a thickness of 0.5mm, your purlins should be spaced no further than 1 metre apart.
How To Support Roof Purlins
While purlins do a lot of heavy lifting and support themselves, they too need to be supported — and knowing how to do this can be tricky.
Purlins are supported by securing them to other stable roof components with fixings, locking them all in together to share each other’s weight. In most cases, your best bet is to secure the purlins to the rafters of the roof.
A rafter refers to the frame of the roof that runs along the length of the building. Ceiling joists are what connect the rafters to the exterior walls to give an open space for an attic or a ceiling area to be filled with insulation further down the line.
When attaching the purlin to the rafter, it is essential that you ensure all the joins and laps are placed over the rafter to provide additional support. Once you have fitted your purlins — and supported them by attaching them to the rafters — it is important to carry out an inspection before work continues.
• Check the framework of the purlin is correct and aligned.
• Check the purlins are levelled. Now is the time to make any adjustments.
• Make sure the purlins are correctly spaced (based on the guidelines above) or the weight of the roofing sheets could cause problems.