Most flat roofs in the South East are one of three systems: torch-on felt, EPDM rubber, or GRP fibreglass. Each has a place. Choosing the wrong one for a particular roof is the commonest flat-roof mistake we see.
At a glance
| Felt (torch-on) | EPDM rubber | GRP fibreglass | |
|---|---|---|---|
| Typical cost per m² | £60 – £90 | £80 – £120 | £90 – £140 |
| Expected life | 15 – 25 years | 30 – 50 years | 25 – 40 years |
| Guarantee (typical) | 10 – 15 years | 20 years | 20 – 25 years |
| Seams | Many, torched | Few or none (single sheet) | None (laid wet) |
| Foot traffic | Light | Light to moderate | Good; ideal for balconies |
| Appearance | Mineral finish | Matt black | Any colour, smooth |
| Best for | Sheds, garages, budget work | Large simple roofs, extensions | Balconies, complex shapes, dormers |
Torch-on felt
Modern three-layer systems are far better than the felt of thirty years ago, and for a garage or outbuilding it remains the cheapest sound option. It is applied with a gas torch, which rules it out near timber cladding, thatch or some insulation. Its weakness is the seams and the edges, which is where it fails first.
EPDM rubber
A single sheet of synthetic rubber, glued down, with no seams on most domestic roofs. It handles UV and movement well and is forgiving on large, simple rectangles like extension roofs. It is less suited to roofs with lots of upstands, pipes and corners, where the detailing gets fiddly.
GRP fibreglass
Laid as resin and glass mat over a plywood deck, then top-coated, so it sets as one seamless skin that follows every shape. It is hard-wearing enough to walk on, which makes it the right choice for balconies and roof terraces. It must be laid in dry weather on a sound, dry deck; rushed GRP on a damp deck is where most GRP failures come from.
Our advice
- Garage or shed, budget matters: felt.
- Extension or large simple roof: EPDM.
- Balcony, terrace, dormer, or a roof with many details: GRP.
- Any flat roof: get the falls right. Standing water shortens the life of all three.