The short answer
Replacing a small flat roof such as a garage or single-storey extension typically costs around £1,000–£3,000 in the UK, with larger or multi-storey work running higher. The biggest driver is the covering: installed prices are roughly £40–£70 per m² for felt, £80–£120 per m² for EPDM rubber, and £90–£130 per m² for GRP fibreglass. On top of the area and material, the figure moves with access, the state of the existing deck, and whether warm-deck insulation is added to meet building regulations. The figures here are typical installed prices for guidance, not quotations.
Price depends mainly on the roof area, the covering you choose, how accessible the roof is, and whether the timber deck and insulation need work. The figures below are typical installed prices for guidance, not quotes.
Typical UK costs
- Small flat roof / garage~£1,000–£3,000
- Felt installed£40–£70 / m²
- EPDM rubber installed£80–£120 / m²
- GRP fibreglass installed£90–£130 / m²
- Main extrasdeck repair, insulation, access
What drives the price
- Roof area: you pay largely per m², so a larger roof costs more — a single garage is a fraction of a wrap-around extension.
- Covering choice: felt is the lowest-priced per m², EPDM rubber sits in the middle, and GRP fibreglass is usually the highest (see the material pages).
- Deck & insulation: if the timber deck has rotted or you upgrade to a warm deck with insulation above, that adds materials and labour.
- Access: a ground-floor garage is simple; a first-floor or dormer roof may need scaffolding or a tower, which adds to the figure.
| Item | Typical figure | Notes |
|---|---|---|
| Small flat roof / garage | ~£1,000–£3,000 | size & covering dependent |
| Felt installed | £40–£70 / m² | shortest-lived covering |
| EPDM rubber installed | £80–£120 / m² | single-ply membrane |
| GRP fibreglass installed | £90–£130 / m² | seamless laminate |
Indicative UK figures for guidance. Sources: Checkatrade and BookaBuilderUK flat-roof cost guides.
Why the covering changes the cost so much
Two flat roofs of the same size can be hundreds of pounds apart purely on the covering. Felt is the lowest-priced to lay but the shortest-lived, so it can cost more over time. EPDM rubber is a single-ply membrane that is quick to fit and mid-priced. GRP fibreglass is laid wet as a seamless laminate and is the most labour-intensive, which is why it usually carries the highest per-m² price. Weighing the upfront figure against how long each lasts is the sensible way to compare — the lifespan page sets that out.
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Frequently asked questions
How much does it cost to replace a flat roof?
A small flat roof such as a garage or single-storey extension typically costs around £1,000–£3,000 in the UK. The covering is the biggest driver — roughly £40–£70 per m² for felt, £80–£120 for EPDM rubber and £90–£130 for GRP fibreglass installed.
Why is the flat-roof price range so wide?
Because roofs differ. The area, the covering you choose, the state of the timber deck and insulation, and how accessible the roof is all move the figure. A measured quote gives the accurate number for your property.
Does adding insulation cost more?
Upgrading to a warm deck with insulation above the structure adds materials and labour, but it is how most replacements meet current building regulations and it improves the energy performance of the room below.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific roof. They are guidance, not a quotation.