Last Updated on July 9, 2026
A flat roof is where most people meet a roofer for the first time. A garage, an extension, a dormer. It is also where the cheapest quote costs the most, because the price gap between materials is small and the gap in how long they last is huge.
The mistake: buying the material, not the lifespan
Flat roofs come in three main materials, and people choose on price alone. That is the wrong lens, because the cheap one is cheap for a reason. It does not last as long.
Here is what they cost per square metre in 2026, and how long each is expected to last:
Felt, the traditional layers. Around £60 to £100 per square metre. Lasts roughly 10 to 20 years.
EPDM, the rubber membrane. Around £80 to £120 per square metre. Lasts roughly 20 to 30 years.
GRP, fibreglass. Around £100 to £160 per square metre. Lasts roughly 25 to 40 years.
What common flat roofs actually cost
A single garage, about 15 to 20 square metres. Felt around £1,200 to £2,000. EPDM around £1,500 to £2,400. GRP around £1,800 to £3,000.
An extension, about 20 to 40 square metres. Felt around £1,800 to £3,500. EPDM around £2,200 to £4,500. GRP around £2,800 to £5,500.
Spend a moment on the maths. On a garage, the gap between the cheapest felt and a mid EPDM might be a few hundred pounds. The gap in lifespan is a decade or more. Paying a little more once is usually cheaper than paying for the whole job twice.
How to read the quote
Check what is under the surface, not just the surface. A good flat roof job includes stripping the old roof, checking and replacing the timber deck where it has rotted, proper falls so water runs off, and new trims and drainage. A quote that only prices the top layer is pricing half the job.
Ask which material, ask the expected lifespan, and ask what happens to the deck underneath if it is wet.
The sharp takeaway
Do not buy the cheapest flat roof. Buy the one whose lifespan fits how long you will own the building. Felt for a short hold, EPDM or GRP when you want to do it once and forget it.
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Typical 2026 UK ranges from public cost data, confirm locally. Sources: Checkatrade, BookaBuilderUK. See also our full roof cost guide.
