Walk onto most flat roof jobs in the UK and you'll see the same material coming out of the van. GRP (Glass Reinforced Plastic, better known as fibreglass) has quietly taken over from felt, lead and bitumen as the go-to system for flat roofs on extensions, garages and porches. The material itself dates back to the 1930s, first developed for insulation and boat building. Roofing came later, but the same properties that made it useful on a hull turned out to work just as well on a flat deck. It's applied as polyester resin and chopped strand glass fibre matting, laid directly onto the roof deck and left to cure into a single hard sheet. No joins, no laps, no seams. Water has nowhere to get in. What makes it worth choosing over older systems isn't just the waterproofing, it's the longevity. A properly installed GRP roof will typically outlast felt by decades, and it won't corrode like lead or lift at the edges like some torch-on systems do in extreme cold. Once it's cured, it's essentially inert. It sits there and does its job. When Was GRP Invented? The story starts in 1938, and calling it a clean-cut invention is a stretch. Russell Games Slayter, working with Owens Corning in the US, is the name most associated with bringing fine glass fibres into commercial use. The material launched as insulation, sold under the brand name Fiberglas, and was also referred to as Glass Wool in its early days. It found its way into boat building first, then automotive and aerospace. Roofing wasn't obvious at the time, nobody was thinking about flat decks when they were waterproofing hulls. But the process translated well, and once contractors figured that out, GRP spread quickly through the trade. It's now the default cold-applied flat roofing system across most of the UK. Why Choose GRP for a Flat Roof? The Practical Advantages GRP has a few properties that make it genuinely well suited to flat roofing in the UK: Lightweight - puts minimal load on the roof structure compared to heavier alternatives Fully mouldable - can be shaped to fit any roof layout, including corners, upstands and details around outlets Walkable - 600gsm GRP is strong enough for maintenance access Long-lasting - a correctly installed GRP roof typically lasts 30 years or more, with some lasting considerably longer Seamless - no joints or seams means no weak points for water to find 100% UV resistant 100% Waterproof The seamless point is worth dwelling on. Felt roofs fail at laps and seams. EPDM relies on adhesive bonds that degrade over time. GRP, once cured, is a single monolithic sheet. There's nothing to peel, separate or crack along a joint. If you want more detail on how the material performs long term, our post on GRP fibreglass roof lifespan covers the specifics. GRP vs Lead Roofing Lead has been used on roofs for centuries, but it's largely been replaced by fibreglass on flat sections over the past two decades. The reasons are pretty straightforward. Cost is the main one. A lead roof costs significantly more to install. And because scrap lead has real market value, lead on extensions, garages and outbuildings gets stolen. GRP has no scrap value, so that problem disappears. GRP matches lead on waterproofing, outlasts it in most cases, and is considerably easier to repair. How Does GRP Roofing Work? What's in a Kit We supply GRP roofing in kits, which is the most practical way to buy it. Each kit contains resin, topcoat, fibreglass matting, hardener, mixing chart and tape, sized for the area you're covering. Everything is matched to work together. Fibreglass roofing trims are ordered separately and are needed to finish the perimeter: drip trims along exposed edges, raised edge trims where the roof meets a parapet, and flashing trims where it meets a wall. The Installation Process GRP is a cold-applied system, which is one of its practical advantages. No heat, no open flame, no torch. The matting is laid onto a prepared OSB or plywood deck, resin is applied and rolled through, and once cured, the topcoat goes on to protect against UV and give the finished appearance. Our video tutorials show the full process from deck prep through to finishing. If you're planning a DIY install, watch those before ordering. Choosing the Right Kit Weight We stock kits at two matting weights: 450gsm - standard weight, suitable for roofs without foot traffic 600gsm - heavy duty, for roofs that need to take occasional walking access If you're unsure which applies to your project, our beginner's guide to GRP roofing kits walks through how to choose. Browse the full range here: GRP roofing kits. Keeping a GRP Roof in Good Shape GRP is low maintenance by nature, but it's not zero maintenance. An annual check, clearing debris from outlets and looking for any surface cracking in the topcoat, will catch small issues before they become expensive ones. Topcoat cracking doesn't mean the laminate is failing. In most cases it's a cosmetic issue that can be resolved with a GRP topcoat refurb kit rather than a full replacement. Our post on GRP roof maintenance covers what to look for and when to act. GRP Roofing from Apex We started out in fibreglass supplying the boat-building trade in Devon, which is where a lot of the practical knowledge came from. When we moved into roofing, we already understood the material and how it behaves. That's been 25 years ago now. Got a question before you order? Ring us on 0800 612 7903 - we're based in Paignton and the people answering know the products. Browse our GRP roofing kits or our fibreglass roofing trims if you're finishing an existing roof. Want to know more about us? Read our story.
