Most people pick a flat roof on price. Fair enough, but the price you pay today isn't the number that matters. The one that matters is what you've spent by 2050, once you've factored in the repairs, the re-lays, and the leak you caused in 2034 trying to fit a skylight into the wrong system. So this is an honest look at the flat roof systems available in the UK right now. Real prices, real lifespans, and where each one actually makes sense. Including the ones we don't sell. The Main Flat Roof Options GRP Fibreglass Liquid resin and matting laid over the deck, cured into one hard, seamless surface. Handles complex shapes and takes foot traffic. Needs dry weather and someone who knows what they're doing. EPDM Rubber A single rubber sheet bonded to the deck. Few seams, so few places to fail. The most common domestic flat roof material in the UK, and on a plain rectangular garage it's hard to argue with. Torch-on Felt Bitumen sheets torched on in layers. Cheap, familiar, and any general roofer can lay it. It also dies earlier and asks the most of you along the way. Lead Outlasts most buildings and needs almost nothing. It's also heavy, expensive, and wants a skilled leadworker, which is why you see it on bay windows and listed buildings rather than garages. Shingles Not a flat roof material. They shed water by gravity and need a pitch to do it. If someone suggests shingles for a genuinely flat deck, get a second opinion. How the Main Systems Compare System Lifespan Installed cost Maintenance Adaptable later? EPDM rubber 40-50 years £60-£95 per m² Lowest Best GRP fibreglass 30-40 years £80-£130 per m² Low Good Torch-on felt 15-20 years £40-£70 per m² Highest Poor Lead 50+ years £150-£200 per m² Very low Good Supply and fit, sound deck. Scaffolding, insulation, deck repairs on top. Add ~20% for London and the South East. No winner here, just trade-offs. The table tells you what each system costs. It doesn't tell you which one is right for your roof, and that comes down to one question: will anyone walk on it? More detail on kit-level pricing in our GRP & EPDM Roofing Kits: Price Comparison by m². What a DIY Kit Actually Costs Buying materials and doing it yourself is a different set of numbers. Ours cover roughly 10m²: Kit type Best for Prices Starting From / m2 450g GRP kit Roofs with no foot traffic £138.60 / 5m² 600g heavy-duty GRP kit Garages, balconies, anywhere that gets walked on £199.44 / 5m² Cure It ONE single-coat Faster application, 20-year guarantee £524.40 / 10m² Classic Bond EPDM flat roof kit Standard extensions and garages £411.19 / 10.5m² EPDM garage roof kit Garages specifically £495.33 / 15m² Materials only. Decking, insulation and tools are separate. Two things people get wrong when ordering. First, 450g and 600g is not a quality tier, it's a foot-traffic decision. 450g on a balcony will fail. Second, people underestimate trims. Every edge needs one, and which trim depends on what that edge butts up against. Both problems disappear if you use the GRP Kit Calculator. Put in your roof dimensions, tell it what's at each edge, and it packages the right kit and trims. For EPDM, the Classic Bond Kit Builder does the same job. There Is No Best Flat Roof Anyone who tells you a single system wins every job is selling that system. Two things worth saying plainly, because they cut against the usual sales pitch. Felt Isn't Always a False Economy In a detached garage or a shed, where you're not heating the space and a leak means a damp lawnmower, the cheapest system that works is often the right system. It's cheap, easy to repair, and any roofer can lay it. Spending EPDM money to protect a bike is not a good trade. GRP Is Not Automatically The Upgrade It's the right call when the roof gets walked on. Terraces, balconies, accessible roofs. The hard, seamless surface handles foot traffic in a way a membrane won't. But it needs dry weather and a skilled installer, and a cold or damp application is how you end up with cracking and delamination. For a roof nobody will ever stand on, you're paying more for a shorter life than EPDM. We sell GRP. We're still telling you that. Planning for What Comes Later This is the bit most people skip, and it's the bit that costs money. Solar If there's any chance of panels, decide now. On EPDM, a ballasted mount avoids cutting the membrane at all. Nothing gets drilled, nothing gets sealed, and the array comes off again without a permanent mark. Penetrations and unapproved mounting methods are what void warranties, not the panels themselves. GRP takes fixings well because the surface is rigid, but every fixing is a permanent hole in a laminate. Skylights and Roof Lanterns Cutting one in later is routine on GRP or EPDM. The skylight itself is the main cost, but reckon on another £75 to £200 to seal it in properly, more for a lantern. On aged torch-on felt, a new penetration is a leak waiting for the right week of rain. If a skylight is even a maybe, our skylights and roof lanterns range is worth a look before you commit to a system. Green roofs Plan these properly. The system runs £90 to £150 per m², and the structure has to carry the weight, so a structural check comes before anything else. Even with no plans today, plans change. Retrofitting into the wrong system is where the money goes. Cheapest to Maintain Every flat roof needs looking after. The gap is in how much. EPDM asks the least. UV-resistant, handles UK temperature swings, and a puncture is a sub-£30 DIY patch. Keep the outlets clear and check it after storms. GRP is also low maintenance, but the wear point is the topcoat. It weathers, and every ten to fifteen years you're looking at a refresh rather than a repair. Not expensive, but not nothing. A topcoat refurb kit handles it. Felt demands the most and dies the youngest. Regular inspection, re-coating every few years, and a full re-lay long before either alternative is tired. Lead needs almost nothing. It just costs three times as much upfront. The honest measure isn't the invoice. It's what you pay per year of service. So Which System Should You Choose? Nobody walks on it, EPDM. Cheaper than GRP, lasts longer, repairs are a DIY job. This covers most garages and most extension roofs. People will walk on it, GRP, 600g. Terraces, balconies, anywhere with regular foot traffic. The rigid surface is what you're paying for. For balconies specifically, a double layer kit. It's a shed and you don't much care, Felt. It'll want replacing in fifteen years, and on a shed that might be fine. Heritage, conservation, or a visible traditional roof, Lead, and budget accordingly. Solar or a green roof in the plan, EPDM, and specify the mounting method before anyone touches the deck. Doing the work yourself? Our video tutorials cover GRP installation, and there's a separate EPDM training centre. Final Thoughts A flat roof is a 20 to 40 year decision made in an afternoon. The two questions that settle it are whether anyone will walk on the roof and whether anything will ever be fixed to it. Answer those honestly, and the material picks itself. Call us on 0800 612 7903 or 01803 523 689, or get in touch. Industry Standards and Best Practice NFRC Flat Roofing Guidance - Technical standards, design notes, and best practice from the National Federation of Roofing Contractors, including updates to BS 6229 for flat roofs. LABC Building Regulations Guidance on Roofs - Clear advice on when building control approval is needed, thermal performance requirements under Part L, and compliance for both new and replacement flat roofs. Planning Portal - Work to an Existing Roof - Official government guidance on Building Regulations for roof repairs and replacements. Apex Resources GRP Kit Calculator - tailored materials list for your exact roof. Classic Bond EPDM Kit Builder - same, for EPDM. Video Tutorials and EPDM Training Centre.
