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.
Flat roof costs at a glance — 2026
Typical fitted prices for a 20m² roof (single garage or rear extension).
Source: BestBuilders 2026 regional cost model · 519 UK towns
Full 2026 rate card
| Item | Typical cost (2026) | Notes |
|---|---|---|
| EPDM rubber, supplied and fitted | £75–£120 per m² | Seamless membrane, 20–30+ year life |
| GRP fibreglass, supplied and fitted | £80–£130 per m² | Hard walk-on finish; must be laid dry |
| Torch-on felt, supplied and fitted | £40–£80 per m² | Cheapest; 10–15 year life |
| Edge trims and drip edges | £12–£20 per metre | Included in good quotes — check |
| Rooflight kerb and upstand | +£250–£600 | Per opening, plus the rooflight itself |
| Replacing rotten deck boards | +£30–£55 per m² | Only known once stripped — agree the rate up front |
| Firring pieces to correct falls | +£150–£400 | Cures ponding permanently |
| Guttering renewed at the same time | +£150–£450 | Cheapest while access is up — see gutter costs |
London and the South East run 15–25% above these figures; the North East, Yorkshire and South Wales typically 5–15% below. Full breakdown in our roof replacement cost guide.
EPDM vs GRP vs felt — which to choose
EPDM is the default recommendation for most garages and extensions: one seamless sheet, flexible in cold weather, quick to lay and very tolerant of damp British installation days. GRP suits roofs that get foot traffic — balconies, terraces, roofs with plant on them — because it cures to a hard shell; the trade-off is it must be laid on a dry day onto a good deck, or it blisters. Felt still has a place on tight budgets and short-horizon buildings, but at £40–£80 per m² against a 10–15 year life it is usually false economy on a house.
How a re-cover runs (1–3 days)
- Strip the old covering and inspect the deck — the honest quote moment.
- Deck repairs at the agreed per-m² rate; firrings added if water has been ponding.
- Insulation — on a habitable room below, a warm-roof build-up (insulation above the deck) meets Building Regulations and stops condensation.
- Membrane laid, bonded and dressed into outlets; trims and flashings fitted.
- Handover — photos of the finished falls and a written guarantee.
Choosing an installer: checklist
- Manufacturer-approved for the system quoted (Firestone/Elevate for EPDM etc.) — approval unlocks the long material warranties.
- A 15–20 year insurance-backed guarantee, not just a verbal promise.
- Falls of at least 1:80 stated on the quote; ponding excluded in writing.
- Photos of five recent flat roofs — edges and outlets tell you more than the field of the roof.
- Three itemised quotes on the same spec: covering, insulation, deck rate, trims, waste.
Red flags
- Overlaying new felt on old without inspecting the deck.
- No mention of falls or outlets on the quote.
- “Liquid rubber over everything” pitched as a permanent fix at a suspiciously low price.
- Cash-only, no written guarantee, or a company with no traceable address.
FAQs
Get 3 Free Flat Roof Quotes — Vetted Installers
BestBuilders matches you with up to 3 vetted flat roof installers experienced in EPDM and GRP. Compare quotes — no cost, no obligation.