A lot of people get in touch when their felt roof starts leaking again. After the second or third repair they start wondering if there’s something that holds up better. GRP fibreglass is one option that comes up regularly for garages, extensions and small flat roofs. GRP won’t suit every roof. Felt fails in a few predictable ways though, and GRP handles most of those better. This guide goes through where it actually helps and the points you still need to watch. The Problem With Felt Felt has been the default for years because it’s cheap and quick. The trouble is it doesn’t cope well with British weather over time. The sun dries the bitumen out. Temperature changes make it move and split at the seams. Once water starts sitting on it, things get worse quickly. Plenty of roofs end up needing work well before the 15 or 20 year mark. That’s why some owners find themselves doing the same job more than once in the same building. How GRP Fibreglass Works Differently GRP builds up a single continuous layer using resin and glass reinforcement. No overlapping joints to come apart later. Once it has cured properly it stays flexible enough to handle normal movement but stays waterproof. The resins we use are marine grade because they handle the constant cycle of wet and dry, hot and cold, better than standard materials. If you want the background on why that matters, we’ve written about it here: What is GRP/Fibreglass Roofing? Lifespan and Day-to-Day Reality When it’s done properly, a GRP roof will normally see you through 25 to 40 years before it needs any serious work. That’s noticeably longer than most felt jobs. The surface stays smoother so moss and dirt don’t grab hold as easily, and there’s less chance of water finding a way in through failed laps. Maintenance is mostly just keeping the edges and any pipes or vents clear. Customers who have dealt with repeated felt problems often say the difference in how much they have to think about the roof afterwards is obvious. Thermal movement can still cause trouble if the system isn’t laid with enough reinforcement or the right topcoat. We’ve covered the practical steps that help avoid cracks and blisters here: Prevent GRP Roof Cracks and Blistering Things Worth Thinking About Before You Choose It It costs more upfront than basic felt. The job also needs decent weather on the day you lay it. Cold or wet conditions can affect how well the resin cures. If your roof has a lot of awkward angles or you’re on a very tight budget, it’s worth looking at EPDM as well. We supply both and can talk through which makes more sense for the actual roof you have. Building Regulations For a straight replacement on an existing roof, you often don’t need building control approval if the area is under 25% and nothing structural is changing. Anything bigger or any insulation upgrade usually does. The official rules are on the Planning Portal if you want to check your situation. Getting the Materials Right Guessing quantities is where a lot of people go wrong. Our GRP Kit Calculator works out the resin, matting, topcoat and trims from your measurements so you don’t end up short or with a load left over. You can see the kits we currently have available here - GRP Roofing Kits Trims make a big difference to how the edges perform long term. We keep the common profiles in stock. Installation and Aftercare The prep work on the deck is where most problems start. It needs to be clean, dry and sound. Once that’s done, following the instructions that come with the kit keeps things straightforward for most competent DIYers on smaller roofs. After it’s down and cured, just check it a couple of times a year. Clear off any leaves or dirt and look at the edges. Small repairs are usually simple if you catch them early. Is It Worth It for Your Roof? For roofs where you want to stop the cycle of repeated repairs, GRP is one of the stronger options available. It won’t suit every budget or every roof shape, but where the conditions are right it gives a longer stretch of trouble-free performance than felt usually manages. If you want to see what a kit would cost for your measurements, the calculator is the quickest way, or have a look at what’s in stock at the moment. Got questions? Give us a call on 0800 612 7903 or email info@apexfibreglassroofingsupplies.co.uk
