Felt, black EPDM rubber and grey GRP fibreglass samples side by side on a workbench

EPDM vs GRP vs felt: the honest comparison

Three systems, one decision. Compared on cost, lifespan, cost per year and how each behaves in real life, with a straight verdict for every scenario. Updated July 2026.

Quick answer: for a garage or any large simple roof, EPDM rubber is the value pick (£90 – £130/m², 30 to 50 years). For a terrace or any roof you walk on, GRP fibreglass earns its premium (£110 – £150/m², 25 to 40 years). Felt (£80 – £110/m², 10 to 20 years) only wins when the immediate budget rules everything.

Every flat roof quote in Britain comes down to these three systems, and most roofers have a favourite they will steer you towards. This page is the referee. The single most useful number in the whole decision is not the price per square metre, it is the price per year of watertight roof, so that table gets centre stage.

The full comparison

	Felt (torch-on)	EPDM rubber	GRP fibreglass
Cost, fitted	£80 – £110/m²	£90 – £130/m²	£110 – £150/m²
Lifespan	10 – 20 years	30 – 50 years	25 – 40 years
Walkability	Occasional only	Light traffic only	Fully walkable
Seams	Many laps	Usually none	None (one moulding)
Install conditions	Dry weather, open flame	Cold-applied, most weather	Dry, mild day essential
Repairs	Easy but short-lived	Quick patch, permanent	Resin work, re-coatable

Cost per year of life: the table that decides it

System	Fitted per m²	Lifespan	Cost per m² per year
Felt	£80 – £110	10 – 20 years	roughly £4.75 – £8.00
EPDM rubber	£90 – £130	30 – 50 years	roughly £2.20 – £3.00
GRP fibreglass	£110 – £150	25 – 40 years	roughly £3.25 – £4.40

Read that middle column twice. Felt, the "cheap" option, costs up to two and a half times more per year of service than EPDM. The £10 to £20 per square metre you save on install day is borrowed, not saved: felt hands you the whole bill again 15 years sooner. Whole-job pricing including decks, insulation and edge details is in the flat roof cost guide.

Verdicts by scenario

Garage roof: EPDM. Big, simple, rarely visited, exactly what a one-piece membrane is for, at the best cost per year on the market.
Extension or kitchen roof: EPDM for most; GRP if you overlook it from a bedroom and care how it looks, or if window cleaners and gutter access mean regular boots on it.
Balcony or roof terrace: GRP, no contest. It is the only one of the three designed to be walked on, and the non-slip topcoat options seal it.
Dormer tops and bay windows: GRP's preformed trims give the neatest small-area finish; EPDM also does these well.
Tight budget, short horizon: felt. Selling within a decade, or roofing a shed or temporary building? Felt's low entry price is the rational pick, eyes open.
Winter deadline: EPDM. It is the least weather-dependent install of the three; GRP is the most.

Whichever system wins, insist on the same three things: a new or verified-sound deck, manufacturer-spec details at every edge and outlet, and a written insurance-backed guarantee. The material is rarely what fails on a flat roof; the installation is. Our guide to choosing a roofer covers the vetting questions.

Get it priced both ways

The smart move on any flat roof job is to have it quoted in two systems, usually EPDM and GRP, and compare against the rates above. Vetted local flat roofers through our free quote service will price both without pushing a favourite.

Price your flat roof in both systems

Up to three itemised quotes from vetted flat roof specialists, in EPDM and GRP, checked against the fair rates on this page. Free, no obligation.

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Flat roof FAQs

Flat roof comparison questions, answered

There is no single winner; it depends on the roof. EPDM rubber is the best value for large simple roofs like garages (£90 to £130 per square metre, 30 to 50 years). GRP fibreglass is best for roofs that get walked on, like balconies and terraces (£110 to £150, 25 to 40 years). Felt is only the right answer when the immediate budget rules (£80 to £110, 10 to 20 years).

EPDM rubber, at roughly £2.20 to £3.00 per square metre per year of life. GRP works out around £3.25 to £4.40, and felt around £4.75 to £8.00 despite having the lowest upfront price. Felt's short 10 to 20 year lifespan makes it the most expensive system over time.

EPDM and felt, yes, with sensible precautions: EPDM adhesives have minimum temperatures and felt needs dry conditions between layers. GRP is the fussy one: its resin will not cure properly on a damp or cold deck, so GRP installs are genuinely weather-dependent and often rescheduled. If your job must happen in January, EPDM is the safest choice.

EPDM: punctures take a bonded rubber patch in under an hour and the repair is as watertight as the original membrane. Felt patches are easy but rarely last because the surrounding felt keeps ageing. GRP repairs need matched resin work and dry conditions, though a worn GRP topcoat can be renewed wholesale to extend the roof's life.

Only if the upfront budget is the deciding factor or the building is short-term. EPDM costs a little more (£90 to £130 per square metre against £80 to £110) but lasts two to three times as long, so it is the better spend on any garage you plan to keep. Felt at 10 to 20 years simply comes around for replacement again sooner.