Why Your Flat Roof Is Probably Failing
If your flat roof is more than 15 years old, it's almost certainly a three-layer bitumen felt system — two layers of sarking felt, nailed down, with a mineral-surfaced cap sheet bonded on top in hot bitumen. That's what got fitted to almost every garage, kitchen extension and bay window roof in Sheffield from the 1960s through the 1990s, and it has a design life of about 15 to 20 years.
The failure mode is always the same. UV light breaks down the bitumen. The cap sheet shrinks and starts pulling away from upstands. Water gets into the laps, freezes in winter, expands, forces the laps apart a bit further next year. Eventually you get a split, then a leak, then ceiling damage, then the phone call to us. The repairs might hold for a winter, but once felt starts to fail in one place, it's usually failing in several.
The good news is that modern flat roof systems are a massive improvement on old bitumen felt. An EPDM rubber roof fitted today should be watertight for 25 to 50 years with no maintenance beyond keeping leaves out of the gutters.
EPDM Rubber — Our Default Recommendation
For most domestic flat roofs — garages, single-storey extensions, dormer tops, porch roofs — EPDM is what we recommend. It's a single sheet of synthetic rubber, factory-made, rolled out in one piece over the whole roof. No seams across the field of the roof, no heat, no open flame. Adhesive-bonded to the deck and dressed up the upstands and around the edges.
The brands we use are Firestone RubberGard and Classicbond — both established American/UK manufacturers with 20-year warranties. A correctly fitted EPDM roof lasts 40 to 50 years in practice, even here in South Yorkshire where the weather is pretty unforgiving. It doesn't crack, doesn't split, doesn't need re-coating. It handles ponding water without degrading. It's the best domestic flat roofing material on the market right now for the money.
A typical garage-sized EPDM replacement (about 20m²) takes two days: day one to strip the old felt and check/replace the deck, day two to bond down the membrane, trim the edges and fit drip-tray flashings. We include gutter alterations and lead flashings up to abutments in the price. No mess, no flames, no fumes — neighbours barely notice we're there.
GRP Fibreglass — When It Makes Sense
GRP fibreglass is the other big contender for domestic flat roofs, and for certain applications it's genuinely better than EPDM. Balcony floors that are regularly walked on. Flat roofs that abut patio doors where you want a seamless, trafficable finish. Roofs with a lot of complex upstands, pipe penetrations or weird geometry — GRP can be moulded around awkward details in a way that sheet materials struggle with.
The downsides are that it's slower to install (three or four days for the same garage, because each layer has to cure), weather-sensitive during fitting (needs a dry spell), and the lifespan is a bit shorter (20 to 25 years vs 40+ for EPDM). It's also significantly more expensive. For a normal garage or kitchen extension, we'd steer you towards EPDM; for a roof terrace or a complicated architectural detail, GRP is often the right answer.
Torch-on Felt — Modern SBS Systems
Torch-on felt gets a bad name because of the old three-layer pour-and-roll bitumen systems, but modern SBS (styrene butadiene styrene) modified bitumen is a genuinely good product. IKO Armourplan and similar two-layer SBS systems give a 15 to 20 year warranty, handle foot traffic better than EPDM, and work well on complex roofs with lots of detailing. It's also significantly cheaper than fibreglass for larger areas.
Where we'd fit torch-on: commercial flat roofs, large complex domestic flats with lots of upstands and penetrations, and conservation areas where the existing roof must be replaced like-for-like.
Repair Versus Replacement
If your existing flat roof is more than 15 years old and leaking, we'd almost always recommend full replacement rather than patching. Patches on old felt are short-term fixes at best — the surrounding material is usually within a year or two of failing in the next spot along. You end up chasing leaks round the roof, spending £400 a go each time, and the ceiling damage compounds.
However, if the roof is reasonably young (less than 10 years) and the damage is localised — a mechanical tear from a fallen branch, a single split at an upstand — we can do a proper permanent repair. EPDM patches bond back to EPDM with the right primer, GRP can be laid over GRP, SBS can be welded in new. We'll tell you honestly which your roof is suitable for.
