Felt, EPDM or GRP: which flat roof should you choose?

Torch-on felt

Three layers of bitumen felt, heat-bonded. £60–£100/m², 15–20 years with a good spec. The cheapest option and fine for a garage or a shed; on a living-space extension, spend a little more.

EPDM rubber

A single sheet of synthetic rubber glued to the deck. £80–£120/m², 25–50 years, no seams on most domestic roofs so nothing to fail. Our usual recommendation for extensions and garages. Not the prettiest surface, and it needs a proper edge trim.

GRP fibreglass

A resin-and-glass laminate applied wet and topcoated. £100–£160/m², 25–30 years, tough enough for balconies and roof terraces, and it can be coloured. Needs a dry day and a dry deck to apply; it can crack on a deck that moves.

The bit that matters more than the covering

Whatever goes on top, the deck must be sound, the falls must take water to the outlet, the upstands must be tall enough, and the roof should be insulated as a warm roof. A cheap covering on a good deck beats an expensive one on a wet, flat, uninsulated deck every time.

Flat roofing covers what we fit and why.