Flat Roof Replacement Cost: Felt vs EPDM vs Fibreglass

Extensions, garages and older outbuildings in Grangemouth and across central Scotland are usually flat or low-pitch. When one starts to fail, the first decision is which covering to replace it with. There are three realistic options, and they differ a lot on both price and how long they last.

Felt is the cheapest, at roughly £40–£95 per square metre depending on the grade and number of layers (Checkatrade, 2026). It’s also the shortest-lived, typically lasting 15–20 years before it needs doing again. EPDM rubber membrane sits in the middle at around £80–£120 per square metre and is usually the best value overall. It’s a single sheet with far fewer joints than felt, with a working life of 40–50 years when properly installed. GRP fibreglass costs more again, roughly £95–£140 per square metre. It forms a fully bonded, seamless surface that copes well with foot traffic or planters, and typically lasts 30–40 years.

Put in real terms, a typical 25–30 square metre garage roof works out at approximately £1,200–£3,500 for felt. EPDM runs £1,800–£3,200, and GRP fibreglass £2,400–£4,200 (BookaBuilderUK, 2026). EPDM’s combination of mid-range price and long lifespan is why we fit it as standard on most domestic flat roofs now. We reserve felt for tight budgets and GRP for roofs that need a hard-wearing, walkable finish.

Price is only half the story, though. A flat roof that is badly detailed at the upstands, outlets and roof edge will fail early, whatever material sits on top. Most of the flat roof leaks we get called out to trace back to a poorly finished edge or a blocked outlet. It’s rarely the membrane itself failing. If your existing flat roof holds standing water for more than 48 hours after rain, that’s usually a falls (drainage gradient) problem. A new covering alone won’t fix it. Worth reading alongside this, if it sounds familiar: our guide on chimney flashing, since flashing details fail much the same way flat roof edges do.

We cover flat roof repair and full replacement across Grangemouth, Falkirk and the rest of our flat roofing service area. Get a free survey and an honest recommendation through our contact page. We also cover Kilsyth and the surrounding area.