Knowledgebase

A Comprehensive Guide to Using Expansion Joints on a GRP Fibreglass Roof

Expansion joints play a critical role in the performance and longevity of GRP (Glass Reinforced Plastic) roofs over a certain size. They accommodate thermal and structural movement, preventing stress and potential damage to the roof. Without expansion joints, the rigidity of GRP materials may lead to cracking, delamination, or structural failure, particularly in large or complex roof designs. This guide explains the design and installation of expansion joints for GRP roofs, providing essential insights for architects, contractors, and installers.

What Are Expansion Joints?

Expansion joints are flexible fibreglass roofing trims designed to absorb movement caused by thermal expansion, contraction, and structural shifts in roofing systems. They are critical for GRP roofs for several reasons. GRP roofs can expand and contract significantly with temperature changes, and expansion joints mitigate the stress caused by this movement. Substrates and buildings naturally settle or shift over time, and expansion joints help maintain the roof's integrity despite these movements. Without expansion joints, GRP roofs are prone to cracking or splitting, delamination of layers, water ingress due to compromised seals, and reduced lifespan of the roofing system.

These expansion joints are available in two different types;

E280 Raised Ridge Roll

The E280 Raised Ridge Roll comes in 3-metre lengths is the most common and can paired with the C5 roof ridge closures to replicate the look of a lead roof.

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G180 Gutter Trim

The other expansion trim is the G180 Gutter Trim which can be used as an inverted expansion joint to aid with drainage. The trim can also be used on for people that don't like the lead roll effect and also for roofs with high foot traffic.

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Designing and Planning Expansion Joints for GRP Roofs

Proper design and planning ensure the effectiveness of expansion joints.

Roof Size

The size of the roof is a crucial factor when designing expansion joints. For roofs larger than 50m² without anything to break up the space, it's essential to incorporate expansion joints to handle thermal movement. Larger roofs may require multiple joints spaced strategically to ensure effective stress distribution.

Roof Design

The overall design of the roof, including slope, curvature, and complexity, influences where expansion joints should be placed if at all. Joints must accommodate the unique structural characteristics of the roof to prevent stress concentrations. If your roof includes features such as windows or a roof lantern, which are popular in residential GRP roofs, you may not need an expansion joint as these features naturally break up the surface area, reducing the need for additional expansion provisions.

Placement

Expansion joints should be placed at predetermined intervals along long expanses of the roof. They should also be installed where different substrates meet and at roof level changes, such as parapets or adjoining sections. Careful planning of joint placement is essential for effective thermal and structural movement management.

Installation Process

Our quick guide on how to install the two different types of expansion joints using the Fibrelast GRP roofing system. If you are still unsure and need more advice, give us a call and we can discuss your project.

E280 Installation

To install the E280 expansion trim an adequate gap in the OSB deck should be cut if necessary, the trim should then be nailed to each end of the decking at 300mm centres. The join over the nails should then be bandaged with fibreglass reinforcement tape using catalysed Fibrelast Base Resin and the laminate can be applied over the trim. To bond these trims together, or to cap them with C5 closures, apply a thin strip of Sharkseal or standard PU adhesive to the inside edge of the overlapping trim and rub it into place.

G180 Trim Installation

As above the OSB decking should be cut to allow for an adequate gap in which to insert the trim and the flanges of the trim should be parallel with the decking. The trim should then be nailed to the decking while the trim edges should be bandaged with fibreglass tape using catalysed Fibrelast Base Resin. The final step would be to apply the main Fibrelast base laminate over the trim finishing with the Fibrelast Topcoat.

What if I Don't Want Expansion Joints on my Flat Roof?

For most roofs, an expansion joint will not be needed but if you have a roof that's over 50m² and you don't want to use expansion joints but still want to use fibreglass roofing then you need to switch to a system like Fibrecoat.

Unlike traditional polyester-based GRP Roofing systems, Fibrecoat is incredibly flexible and does not require expansion joints on any roof size, from 50 to 5,000 square metres and beyond. It's also low odour, styrene free and doesn't require a catalyst to cure the resins.

So if you're still at the planning stage of your roofing project and are worried about thermal expansion and contraction issues with your roof check out Fibrecoat.