Flat roof options compared: EPDM rubber vs GRP fibreglass vs felt

If you've got a flat roof on an extension, garage, porch or dormer that's reaching the end of its life, you've basically got three modern choices. Here's the plain-English version of each, with no jargon.

EPDM rubber

A single sheet of synthetic rubber, often laid in one piece with no joins on smaller roofs. It flexes with the building, copes well with our temperature swings, and typically lasts 30–50 years. It's our usual recommendation for most domestic flat roofs.

GRP fibreglass

A glass-reinforced plastic laid wet and cured into a hard, seamless finish. Tough, looks neat with a crisp edge trim, and lasts 25–30+ years. It needs dry weather and a skilled hand to lay properly, but the result is excellent on the right roof.

Felt (the old way)

Traditional torch-on felt is cheaper up front and still has its place, but modern multi-layer felt typically lasts 10–20 years — less than rubber or fibreglass. If a roof's been done in felt and keeps failing, it's usually worth moving to EPDM or GRP next time.

Which should you choose?

• Most house extensions and dormers: EPDM rubber — long life, great value, flexes with the building
• A flat roof you'll see or walk near, wanting a hard neat finish: GRP fibreglass
• Tight budget or a quick patch on a short-term building: felt

Whatever it is, the detailing at the edges, upstands and around any pipes is where flat roofs live or die — that's the bit to get a proper roofer to do.