Flat Roof Installers: Cost & Options 2026 (UK)
A new flat roof costs £75–£120 per m² fitted in 2026, so a typical 20m² garage or extension roof comes in at £1,500–£2,400. The covering you choose is the biggest decision: EPDM rubber and GRP fibreglass both last 20–30+ years and dominate quality work in 2026, while cheaper felt is fading out. Here is what each system costs, how they compare, and what to look for when choosing a flat roof installer.
2026 flat roof costs by system
| System | Cost per m² (fitted) | Lifespan |
|---|---|---|
| Felt (built-up / torch-on) | £40–£80 | 10–15 years |
| EPDM rubber membrane | £75–£110 | 20–30+ years |
| GRP fibreglass | £90–£120 | 20–30 years |
| Typical 20m² garage/extension roof | £1,500–£2,400 | — |
| New deck / firrings (if needed) | +£300–£800 | — |
EPDM vs GRP vs felt
EPDM rubber is a single seamless sheet, quick to fit, flexible in cold weather and very durable — the popular choice for garages, extensions and dormers. GRP fibreglass is a hard, seamless resin-and-matting system with a neat finish and integral trims; it is excellent on balconies and roofs that get foot traffic but must be laid in dry conditions. Felt is the cheapest but the shortest-lived and is increasingly replaced by the other two on quality jobs.
What good flat roof installers include
- Correct falls: firring pieces to give a slope so water drains rather than ponding.
- Sound deck: new OSB or ply where the old deck is soft or rotten.
- Proper upstands, trims and drips at edges and abutments.
- An insurance-backed or manufacturer guarantee — typically 10–20 years.
How to choose a flat roof installer
Get three written quotes for the same system and specification, and check each installer is experienced in that covering — EPDM and GRP need different skills. Ask for recent local examples, confirm public liability insurance, and make sure the quote states the covering, deck works, falls and guarantee. The cheapest felt quote often costs more over 20 years than a slightly dearer EPDM or GRP roof that lasts.
FAQs
Related guides
Get 3 Free Flat Roof Quotes — Vetted Installers
BestBuilders matches you with up to 3 vetted, insured flat roof installers experienced in EPDM and GRP. Compare quotes — no cost, no obligation.