Flat Roof Replacement Cost: Felt vs EPDM vs GRP
A tired felt flat roof that splits, blisters and pools water is usually more cost-effective to replace than to keep patching. The price depends on the size, the access, whether the deck needs replacing and which covering you choose. Here are realistic UK figures. For typical prices, see our roof repair cost guide.
Rough figures
A single garage or small extension flat roof: felt £900–£1,800, EPDM rubber £1,200–£2,500, GRP fibreglass £1,500–£3,000. Larger roofs are priced per square metre. Replacing a rotten timber deck adds £25–£45 per m2. All need a free survey for a firm price.
Felt (built-up bitumen)
Modern torch-on felt in two or three layers is the budget option and, fitted well, lasts 15 to 20 years. It is proven and easy to repair, but it has seams, and seams are where flat roofs eventually fail. Best suited to larger commercial-style roofs and where budget is the priority.
EPDM rubber
A single sheet of EPDM rubber membrane with no joins across most domestic roofs — nothing for water to work into. It flexes with temperature, shrugs off UV and lasts 30 to 40 years or more. It is the covering we fit most on garages, extensions and dormers. Slightly more than felt, and worth it for the seamless finish and the guarantee.
GRP fibreglass
Glass-reinforced polyester laid wet and cured into one solid, seamless shell. Very hard-wearing, takes foot traffic, and can be finished in different colours and with a non-slip surface for balconies. The most expensive of the three and weather-dependent to install (it needs dry conditions to cure), but the toughest result.
What moves the price
Size and access are the big ones — a roof you can reach from a stepladder is far cheaper than one needing a scaffold tower. The condition of the deck: soft or rotten boarding has to come off and be replaced. Insulation: a warm-roof build to current building regs adds a rigid insulation layer. New edge trims, drip details and any parapet flashings. And whether the old covering has to be stripped and taken away.
Flat roof replacement – typical cost
| Covering | Garage / small extension | Per m2 (larger roofs) | Life |
|---|---|---|---|
| Felt (torch-on) | £900 – £1,800 | £60 – £90 | 15–20 yrs |
| EPDM rubber | £1,200 – £2,500 | £80 – £120 | 30–40 yrs |
| GRP fibreglass | £1,500 – £3,000 | £90 – £140 | 25–40 yrs |
| New timber deck (if needed) | — | + £25 – £45 | — |
Frequently Asked Questions
Is it worth repairing a flat roof or replacing it?
A single split or a lifted lap on an otherwise sound roof is a repair. Once the covering is blistered and cracked across the whole surface, or it has been patched several times, replacement in EPDM or GRP is better value and comes with a long guarantee.
Which flat roof covering lasts longest?
EPDM rubber and GRP fibreglass both last far longer than felt — typically 30 years or more — because they are seamless. EPDM is more forgiving of movement; GRP is harder-wearing underfoot.
Can a flat roof be replaced in a day?
A garage or small extension roof in felt or EPDM often can be, weather permitting. GRP needs dry conditions and curing time. Larger roofs or a deck replacement take longer.
Do I need building regulations for a flat roof replacement?
If you replace more than about a quarter of the roof area you generally need to bring the insulation up to current standards, which means a warm-roof build. We handle that as part of the job.
Related Reading
EPDM vs fibreglass vs felt flat roofing
Read moreComparing the three flat roof coverings.
Warm roof vs cold roof explained
Read moreWhere the insulation sits and why it matters.
How much does roof repair cost in the UK?
Read moreRealistic UK costs by job type.
Roof repair vs roof replacement
Read moreDeciding between a repair and a full re-roof.
Flat Roof Ready for Replacement?
We replace garage, extension and dormer flat roofs in EPDM rubber, GRP fibreglass and felt across the South Wales valleys — fixed written quote after a free survey.