Newly finished EPDM rubber flat roof on a UK extension

How much does a flat roof cost in the UK?

Real 2026 prices per square metre for felt, EPDM rubber and GRP fibreglass, plus typical garage and extension totals. Prices updated July 2026.

Quick answer: flat roof replacement costs £80 to £150 per m² in 2026 depending on material. A typical single garage runs £1,400 to £3,000 and a 25m² extension roof £2,300 to £4,000. Felt is cheapest upfront, EPDM rubber usually cheapest per year of life.

Flat roofs are priced per square metre, so the two questions that set your bill are how big the roof is and what you put on it. This guide covers the three materials that dominate UK domestic flat roofing, what whole jobs actually cost, and the extras that catch people out. For work descriptions and what a good installation looks like, see the flat roofing service page, or get a tailored figure from the roof cost calculator.

Flat roof cost per m² by material (2026)

Material	Supplied & fitted per m²	Lifespan
Felt (torch-on)	£80 – £110	10 – 20 years
EPDM rubber	£90 – £130	30 – 50 years
GRP fibreglass	£110 – £150	25 – 40 years

Judge on cost per year of life, not the day-one price. Felt is the cheapest to lay but the first to fail; EPDM costs a little more and can last two to three times as long, which is why it usually wins the value calculation. Our flat roof material comparison puts all three side by side on cost, lifespan, looks and repairability.

What whole jobs cost

Job	Felt	EPDM	GRP
Single garage (approx 18m²)	£1,400 – £2,000	£1,600 – £2,600	£1,900 – £3,000
Extension roof (approx 25m²)	–	£2,300 – £3,500	£2,800 – £4,000
Small dormer	£600 – £1,200

Garages are the classic entry-level flat roof job; if yours is the one that needs doing, the garage roof cost guide goes deeper on that job specifically, including asbestos removal and pitched conversions.

Roofer applying GRP fibreglass resin with a roller

Extras that change the bill

Warm-roof insulation upgrade: adds £40 to £60 per m², and is often required by building regulations when you replace the covering wholesale. It also fixes the condensation problems cold roofs suffer; see warm vs cold roofs for how the build-ups differ.
Replacing rotten decking: adds £20 to £35 per m². You rarely know how much is needed until the old covering comes off, so agree the per-m² rate in the quote before work starts.
New rooflight kerb: £300 to £600, best done while the roof is open rather than retrofitted later.

Red flag: a quote that undercuts everyone else on an extension roof usually means the insulation upgrade has been quietly left out. If the covering is being replaced wholesale, building regulations thermal rules often apply, and a roofer pricing without insulation is pricing a job that may not pass sign-off. Ask every quote to state the insulation spec in writing.

Felt, EPDM or GRP: which should you pick?

If the roof is a plain rectangle you will rarely step on, and budget is tight, felt still does a job. If you want the best value over the roof's life, EPDM's long lifespan usually makes it the cheapest per year despite the higher day rate. If the roof has upstands, complex details or regular foot traffic, GRP's hard seamless shell is worth the premium. The deep dives on EPDM rubber and GRP fibreglass cover installation, guarantees and failure modes for each.

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Flat roof FAQs

Flat roof cost questions, answered

Torch-on felt is the cheapest flat roof material upfront at £80 to £110 per square metre fitted in 2026, against £90 to £130 for EPDM rubber and £110 to £150 for GRP fibreglass. Felt is also the shortest-lived of the three, so it is only the cheapest option if you judge on the day-one price rather than cost per year of life.

It depends on the material. Torch-on felt typically lasts 10 to 20 years, GRP fibreglass 25 to 40 years, and EPDM rubber 30 to 50 years. Installation quality matters as much as the material: a poorly detailed GRP roof can fail years before a well-laid felt one.

Neither is better outright; they suit different roofs. EPDM rubber flexes with the building and comes in large single sheets, so it suits bigger, simpler roofs with few penetrations. GRP fibreglass sets as a hard, seamless shell, so it is harder wearing under foot traffic and handles complex shapes, upstands and details better. On a plain garage roof EPDM is usually the value pick; on a walked-on or awkward roof GRP earns its premium.

Usually yes when you replace the covering wholesale rather than patching it. Replacing more than a limited area of the roof counts as renovation of a thermal element, so thermal upgrade rules often apply and the insulation may need to be brought up to current standards at the same time. A reputable roofer will handle the notification through a competent person scheme.

GRP fibreglass yes: it cures into a rigid laminate and is designed to take foot traffic, which is why it is the usual choice for balconies and roofs with regular access. EPDM rubber tolerates occasional careful access but is not designed for regular walking, so fit paving slabs or walkway pads over any route you will use often. Felt sits closer to EPDM: occasional access only.