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Expansion joints for a fibreglass roof

When does a fibreglass roof need expansion joints?

What is expansion and contraction?

Flat roofs, popular in both residential and commercial architecture here in the UK, are particularly susceptible to the effects of temperature fluctuations. The phenomena of expansion and contraction are central to understanding how these roofs behave under varying conditions and ensuring their longevity.

Expansion occurs when the fibreglass roofing materials absorb heat, causing them to increase in size. During hot weather, the roofing membranes, insulation, components, and even the structural decking of a flat roof expand. If this expansion is not properly accounted for in the design and construction of the roof, it can lead to significant issues.

Contraction happens when temperatures drop, causing the materials to lose heat and shrink. This size reduction can also have detrimental effects. Just like expansion, contraction can lead to cracks in the roofing membrane or between joints, and increased brittleness in some materials, leading to cracking or delamination.

What are Expansion joints and do I need them?

Fibreglass roofs created using traditional polyester-based resins and topcoats are best suited for strength rather than flexibility and even though they are advertised as flexible they would still be susceptible to cracking on larger roofs.

Resin flexibility is measured by something called elongation at break (EAB) and can be found on the product's technical data sheet. Elongation at break measures how much a material can flex before it fractures, products with lower EAB percentages like polyester-based fibreglass roofing systems will tend to be suitable for smaller projects and may require additional products to increase flexibility.

Our guidelines for the size of a fibreglass roof is up to 50m² without an expansion joint, which is why our kits stop at that size. Anything over that, with nothing to break up the space like windows or a south-facing roof that is constantly in the sun,  you may need to consider installing an expansion joint or changing the system to a more flexible product like Fibrecoat.

Expansion joints also known as an E280 Raised Ridge Roll and a G180 Gutter Trim are made from glass-reinforced plastic and come in 3-metre lengths. The raised ridge roll also allows you to create a ridge detail on the roof while the G180 allows the installation to be concealed. Generally speaking, you would need one expansion joint per 50m² of roof.

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