Fibreglass (GRP) Flat Roof Cost & Options in 2026
A fibreglass (GRP) flat roof typically costs £75–£120 per m² fitted in 2026, or roughly £1,500–£3,000 for a single garage. GRP (glass-reinforced plastic) is laid as a wet resin and matting system that cures into one seamless, joint-free surface. It handles foot traffic and ponding water well, which makes it popular for garages, dormers and single-storey extensions. Below we break down real 2026 prices, lifespan, and how fibreglass stacks up against felt and EPDM rubber.
Fibreglass flat roof cost breakdown (2026)
| Roof size / job | Typical cost (2026) | Notes |
|---|---|---|
| Single garage (~15 m²) | £1,500–£3,000 | Supply and fit including trims and a coloured topcoat. |
| Porch or small extension (~20 m²) | £2,000–£3,600 | Price depends on access and how many upstands and edges are involved. |
| Larger extension (~30 m²) | £2,800–£4,500 | Scaffold and complex detailing can push the upper figure higher. |
| Supply & fit, per m² | £75–£120 | Varies with deck condition, topcoat finish and edge detailing. |
| Strip & dispose of old roof | £250–£600 | More if a new OSB deck is needed or old felt has to be removed. |
How fibreglass compares with felt and EPDM rubber
Traditional felt is the cheapest option upfront, often £40–£70 per m², but a torch-on felt roof usually lasts 10–20 years and relies on heat-welded joints that can lift over time. EPDM rubber sits in the middle of the range and is fitted as a single stretched sheet, which is fast and forgiving on awkward shapes. Fibreglass costs more than both but cures into a completely seamless, rigid GRP shell with no joints to fail, and it takes foot traffic far better — which is why it is the usual choice for balconies, dormers and roofs you occasionally walk on.
How long does a fibreglass roof last?
A properly installed GRP roof will typically last 20–30 years, and many carry a 20-year materials or workmanship guarantee. Longevity comes down to the quality of the timber deck underneath and the skill of the fitter: the laminate must be applied at the right thickness and cured in dry, warm conditions. Get those right and a fibreglass roof needs almost no maintenance beyond an occasional clean and a check of the trims.
Is a GRP fibreglass roof worth it?
For a small, flat or low-pitch area that you want to fit once and forget, fibreglass is usually worth the extra outlay — the seamless finish, walk-on strength and long lifespan justify the higher price per m². For a large, simple roof on a tight budget, EPDM rubber can deliver similar durability for less. Always get at least three itemised quotes so you can compare the deck preparation, laminate thickness and guarantee, not just the headline figure.
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