A flat roof replacement in Exeter costs from £900 for a small garage to £4,500+ for a large rear extension depending on area, system choice and deck condition. GRP fibreglass is the most popular system in Devon and the one we install most frequently — this guide explains why and what the alternatives cost.
| Job Type | Typical Cost | Notes |
|---|---|---|
| GRP fibreglass — garage (up to 20m²) | £900–£1,400 | Single day installation. 25-year design life. |
| GRP fibreglass — rear extension (20–40m²) | £1,400–£2,500 | Standard Devon extension. 1–2 days. |
| GRP fibreglass — large (40–60m²) | £2,500–£3,800 | Larger extensions, garage roofs, complex areas. |
| EPDM rubber — similar area | £800–£3,200 | 10–15% less than GRP. Similar lifespan. |
| Felt (torch-on) — re-cover | £500–£2,000 | Shorter lifespan (10–15 years). Not our recommendation. |
| Deck replacement (per m²) | £30–£60/m² | Additional cost if deck is compromised. Surveyed scope. |
All figures are indicative for Devon. Exact costs depend on site survey. Call 01392 759 295 for a free, no-obligation quote.
GRP fibreglass and EPDM rubber both provide 25-year performance in Devon’s climate. GRP is slightly more expensive but provides a harder, more impact-resistant surface and is easier to inspect for damage. Felt is cheaper but has a 10–15 year lifespan in Exeter’s rainfall environment — we do not recommend it as a long-term solution.
Flat roof cost is primarily driven by area. Irregular shapes, penetrations (pipes, rooflights, AC units) and complex perimeter details add labour time.
A GRP or EPDM installation over a compromised deck produces a surface that fails prematurely as the deck flexes beneath it. We survey deck condition before quoting and include deck repair or replacement where required. On older Wonford, Whipton and Pinhoe extensions this is more frequently needed than on newer properties.
A correctly designed flat roof has adequate fall toward the outlet and an outlet sized for the actual catchment area and rainfall intensity. Exeter’s above-average rainfall means sizing to minimum standard is not adequate on larger roofs. Correct drainage design at installation eliminates ponding — a roof designed for ponding fails faster at the waterline.
For Exmouth and Dawlish properties, perimeter trims and fixings should be marine-grade. GRP’s seamless surface performs particularly well in the coastal environment as there are no joints for salt aerosol to penetrate.
A properly scoped flat roof quote should state: the system to be installed (GRP, EPDM or felt); the material specification and thickness; the deck condition assessment finding and what deck work is or is not included; drainage design (outlet size, fall direction); perimeter and trim detail; waste disposal; and the guarantee period for both materials and workmanship. A quote that describes the system as ‘GRP flat roofing’ without specifying laminate thickness, topcoat system and trim type is not a complete specification.
Any flat roof quote should include a statement on deck condition. A quote that does not mention the deck is either not surveying it or planning to install over whatever is there.
Felt is a legitimate roofing material but has a shorter lifespan in Devon’s climate. A roofer recommending felt over GRP for a Devon property without explaining the lifespan difference is not giving you complete information.
Fall direction, outlet size and drainage detail should be stated in the quote. A flat roof installed without correct drainage design will pond water regardless of the system quality.
GRP and EPDM flat roofing comes with manufacturer warranties of 20–25 years. A roofer offering a 5-year or shorter guarantee on these systems is either using inferior materials or not confident in the installation quality.
“GRP on our rear extension. Deck condition was assessed, one board replaced. Full drainage spec included. 25-year guarantee. Correct job done properly.”
“Chose GRP over re-felting on our Wonford extension. Third felt cover would have been money wasted. GRP will outlast the rest of the house.”
“Coastal property in Exmouth. GRP with stainless trims. They specified the coastal detail correctly without being asked. Confident choice.”
GRP from £900 for a small garage to £3,800+ for a large extension. EPDM is 10–15% less. Free survey and quote. Call 01392 759 295.
Yes, for Devon’s wet climate. GRP’s seamless surface eliminates the laps and joints where felt fails. GRP lasts 25+ years vs 10–15 for felt. The cost difference is recovered within a single felt re-cover cycle.
GRP and EPDM: 25–30 years correctly installed. Felt: 10–15 years in Devon’s above-average rainfall.
Like-for-like replacement does not. Changing the roof structure, adding a roof terrace, or work on a listed building may require consent. We advise at survey stage.
A standard rear extension or garage is typically completed in a single day. Larger or more complex areas take 1–2 days.
Yes — GRP patch repair on localised GRP failure, and emergency felt patching while replacement is arranged. We advise honestly on repair vs replacement at the survey. Call 01392 759 295.
If your flat roof has been re-covered once already, GRP is the correct choice. Another felt layer provides 10–15 years. GRP provides 25+. The cost difference over 20 years consistently favours GRP.
Free survey, no call-out fee, no obligation. An honest price from a Devon roofer who turns up when they say they will.
01392 759 295