Every week we answer the same questions on the phone. How much does a fibreglass roof cost? Can I patch it instead of replacing it? Which kit do I need for a garage roof nobody walks on? Some of these need a full guide to answer properly, so where that's the case we've linked one. The rest we've answered here in a couple of lines. Prefer to just ask? The chat on this page goes straight through to Paul and the team, all sitting in the same office in Paignton, or call 0800 612 7903. GRP Basics What is GRP/fibreglass roofing? GRP (glass reinforced polyester) is a flat roofing system built by laying glass fibre matting into liquid resin on the roof deck, then sealing it with a coloured topcoat. The result is one seamless, waterproof layer with no joints for water to find. Full explanation in our guide: What is GRP/Fibreglass Roofing? GRP vs EPDM: which is better for UK homes? GRP gives a hard, seamless finish that takes foot traffic well and suits complex roof shapes, while EPDM rubber goes down faster and flexes more, which makes it popular for sheds, garages and simple rectangles. Our price comparison by m² and the chemistry behind both systems will help you decide for your roof. Do container homes and unusual buildings need fibreglass roofs? They don't need one, but GRP suits them well because it bonds to a properly prepared deck of almost any shape and copes with the movement these structures see. We cover tiny homes, modular buildings and garden rooms in Roofs for all House Types. Costs and Choosing a Kit How much does a fibreglass roof cost in 2026? The 450g garage kit costs about £140, and the 600g kit costs about £200. What you pay overall depends mostly on labour and whether the deck needs replacing. We compare GRP against EPDM, felt and lead, including maintenance costs over 25 years, in How Much Does a Fibreglass Roof Cost in 2026? How do GRP and EPDM kit prices compare per m²? Kit prices fall into three brackets, from budget DIY kits through standard 450g systems to premium single-coat products like Cure It ONE. The full breakdown with per-metre pricing is in GRP & EPDM Roofing Kits: Price Comparison by m². Budget, standard or heavy-duty: which GRP kit does my project need? A 450g kit suits roofs nobody walks on, while balconies, walkways and anywhere you'll stand need a 600g heavy-duty kit. Our comparison of all three systems is here: Budget, Standard or Heavy-Duty: Which GRP Roofing Kit Does Your Project Actually Need? What GRP supplies do roofers actually use? Working roofers keep it simple: quality chopped strand matting, roofing-grade resin and topcoat, the right trims, and a small set of rollers and brushes. We asked the trade and wrote it up in Best GRP Roofing Supplies: What Roofers Actually Use. Installation and Materials How do I estimate materials for a fibreglass flat roof? Measure the roof area, add the upstands and edges, then work out matting, resin, topcoat, catalyst and trims from there. Our materials estimation guide walks through a worked 24m² example, or let the GRP Kit Calculator do the maths for you. How much resin do I need per m²? The trade rule of thumb is around 1.5kg of resin per square metre when laminating 450g matting, plus extra for detailing and a separate allowance for topcoat. Exact quantities depend on your roof, so use the GRP Kit Calculator or our estimation guide before ordering. How do I prepare a flat roof for fibreglass? Strip the old covering back and board out with fresh OSB3. GRP needs a solid, dry deck under it, and if you laminate over damp or springy boards the roof will fail no matter how good the resin is. Can you overlay a GRP roof instead of stripping it? Yes, if you use a system designed for it. Products like Ultra-Flex go directly over asphalt, concrete and metal without re-boarding, and our complete overlay systems range covers the other options. Standard GRP kits still need a fresh deck. For GRP and EPDM projects, can the same resin be used? No. GRP is built with polyester resin and glass matting, while EPDM is a rubber membrane fixed with contact and deck adhesives, and mixing the two causes bonding failures and heat stress. The full explanation is in Can the Same Resin Be Used for GRP and EPDM Projects? Repairs, Problems and Maintenance Can a fibreglass GRP roof be repaired instead of replaced? Often, yes. Cracks, pinholes and a chalky topcoat all take a repair kit or a topcoat refurb. The exception is a soft deck. If the boards have gone, resin on top won't save it. When to fix something and when not to: Can Fibreglass GRP Roof Be Repaired Instead of Replaced? Can an EPDM roof be repaired instead of replaced? Punctures, lifted seams and small splits all patch up with primer and tape. The membrane underneath usually has years left in it. More detail here: Can an EPDM Roof Be Repaired Instead of Replaced? Why do GRP roofs crack or blister, and what can I do to stop it? Heat. The roof expands in summer and contracts overnight, and if there's nowhere for that movement to go, the laminate cracks. Bad prep and skipped expansion joints are usually behind it. Full explanation: Prevent GRP Roof Cracks and Blistering How does GRP handle British rain, snow and storms? A seamless GRP laminate has no joints to fail under standing water or wind uplift, which is a big part of why it lasts 25 to 40 years here. The detail is in GRP Roofing in the UK: How Fibreglass Handles Rain, Snow & Storm Damage. How can I prevent moisture damage to my ceilings and walls? Water comes in because the covering is broken, or it stays trapped inside because there's no barrier for vapour and no way for damp air to leave. Both end up looking the same on your ceiling. Prevention and fixes, including where vapour barriers fit in, are in Moisture Damage to Ceilings and Walls: Prevention and Solutions. Regulations and Performance Are GRP flat roofs fire resistant, and what do UK regulations say? GRP itself will burn, which is why Approved Document B and the BROOF(t4) classification matter when a roof sits near a boundary or another building. Our guide to the regulations is here: Fire Resistance of GRP Flat Roofs: What UK Regulations Say, and our fire retardant kits meet the relevant classifications. Can insulating a fibreglass flat roof cut my heating bill? Yes. A warm roof build-up with rigid insulation under the GRP laminate cuts heat loss through one of the biggest weak points in the building. How it works and what it saves: Insulating Flat Roof: How Fibreglass Can Save You on Your Heating Bill. EPDM Rubber Roofing What's in the Apex EPDM range? Everything from complete ClassicBond flat roof kits to shed, garage and dormer kits, plus adhesives, trims and tools. The full rundown is in The Complete Guide to Our EPDM Roofing Range, or build a bespoke kit with the EPDM Kit Builder. What's the best rubber roof kit for a shed, and how fast is delivery? The SkyGuard shed rubber roof kit is our pick: one-piece EPDM membrane, straightforward DIY fit, delivered in 2 to 5 days. We compare it against felt in Skyguard Shed Rubber Roof Kit: Best EPDM Shed Roof Kit in the UK. Can I walk on an EPDM roof without tearing it? For maintenance, cleaning gutters, the odd trip up there, yes. The membrane handles occasional foot traffic fine. What tears it is grit trapped under your boots, so brush the area first, and if the roof gets regular use, put walkway pads or paving down rather than walking on bare rubber. Can a dropped tool or hammer make a hole in EPDM? A blunt knock usually won't, the rubber flexes and shrugs it off. A sharp edge or corner landing hard can puncture it, especially over a gap between boards where the membrane has nothing behind it. The good news is a puncture patches in minutes with primer and tape. Can I fix an EPDM roof with a GRP patch? No. Polyester resin doesn't bond to rubber, so the patch lifts at the edges and you've got a leak with a lid on it. EPDM gets repaired with EPDM: primer, seam tape or a rubber patch. How that works: Can an EPDM Roof Be Repaired Instead of Replaced? Trims and Finishing Which edge trims does my GRP roof need? Almost every GRP roof uses a drip trim at the gutter edge, raised edge trims (like the B300) on the other perimeters, and wall flashing trims (D260/D300) where the roof meets brickwork. Our two trim guides cover the details: GRP Fibreglass Roof Edge Trims Explained and Choosing the Right Trims & Flashings for Complex Roof Designs. Are EPDM edge trims the same as GRP trims? Can I use one with the other? No, they're separate systems. GRP trims are rigid fibreglass profiles that get laminated into the roof with resin, while EPDM has its own edge trims designed for the membrane to tuck into or bond against. Resin won't bond to rubber and EPDM adhesive won't hold a GRP trim, so mixing them ends the same way as mixing the resins. The trims in our EPDM range are covered in The Complete Guide to Our EPDM Roofing Range. Beyond the Roof How do adjustable pedestals work for decking on a flat roof? Pedestals sit on the finished roof and support decking or paving above it, so you get a level terrace without puncturing the waterproof layer. Installation and spacing are covered in How to Install Adjustable Decking Pedestals. Can I fit a skylight or roof lantern in a flat roof? Yes, and a flat roof is the easiest roof type to fit one on. The opening is built up on a timber kerb, the GRP or EPDM is dressed up and over it, and the rooflight sits on top. We stock SkyPod skylights, Korniche lanterns and flat glass rooflights in a range of sizes. What are Hyperion composite cladding boards? Wood-effect composite cladding for exterior walls that doesn't need painting or sealing and stands up to UK weather. The introduction is here: Upgrade Your Exterior: Introducing Hyperion Composite Cladding Boards. I've put solar panels on my GRP roof, can I just topcoat the anchor points? No. The topcoat seals the surface, but it isn't waterproof on its own, and water will track down a bolt that goes through the laminate. Any fixing that penetrates the roof needs bandaging first, a patch of matting and resin laminated over the base plate, then topcoat over that. More on panels and flat roofs: Are Flat Roofs Better for Solar Systems? Still Got a Question? The chat on this page goes through to Paul and the team, or call 0800 612 7903 or 01803 523 689 and we'll talk you through it. To spec your roof, use the GRP Kit Calculator or EPDM Kit Builder, or contact us through the site.
