The short answer
A GRP (glass-reinforced polyester) fibreglass flat roof typically costs around £90–£130 per m² installed in the UK, which usually makes it the highest-priced of the common flat-roof coverings. It costs more because it is laid wet on site as a seamless laminate — layers of resin and glass matting built up over a board deck and finished with a coloured topcoat — which is more labour-intensive than rolling out a membrane. In return you get a hard, joint-free surface that can take light foot traffic and typically lasts around 20–25 years when correctly installed. It suits balconies, dormers and roofs where a tough, walkable finish matters.
GRP is the fibreglass option — a resin-and-matting laminate laid in place rather than a pre-made sheet. Here is what it costs, why, and where it earns its higher price.
GRP at a glance
- Installed cost£90–£130 / m²
- Typical lifespan~20–25 years
- Finishseamless, hard, walkable
- Laidwet, on site, in layers
- Best forbalconies, dormers, foot traffic
Why GRP costs what it does
GRP is built up by hand: a fibreglass matting is bonded to the board deck with resin, then a pigmented topcoat is rolled over the top, curing into one seamless skin with no joints to fail. That hand-laid, weather-sensitive process is more labour than unrolling a rubber membrane, which is why GRP usually sits at the top of the per-m² range at roughly £90–£130 per m² installed. The pay-off is a hard surface with no seams and a clean, tiled-look finish — useful where the roof is seen or walked on.
| Item | Typical figure | Notes |
|---|---|---|
| GRP installed | £90–£130 / m² | highest of the common coverings |
| Typical lifespan | ~20–25 years | correctly installed & maintained |
| Small roof example | ~£1,800–£4,200 | garage / extension, size dependent |
Indicative UK figures for guidance. Sources: Checkatrade and BookaBuilderUK flat-roof cost guides.
When GRP is worth the extra
Because it cures to a hard, joint-free surface, GRP handles light foot traffic and a smart, seamless look better than a membrane, so it is a common choice for balconies, walk-on terraces and visible dormer roofs. It is laid wet, so it needs dry, warmer conditions to cure properly and skilled application — a poorly cured GRP roof can craze or delaminate. If your roof is simply a hidden garage top, a membrane may give similar protection for less; if it is seen or used, the seamless finish can justify the price.
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Frequently asked questions
How much does a GRP fibreglass roof cost per m²?
Typically around £90–£130 per m² installed in the UK, which usually makes it the highest-priced of the common flat-roof coverings because it is laid wet as a seamless laminate rather than rolled out as a membrane.
How long does a GRP fibreglass roof last?
A correctly installed and maintained GRP roof typically lasts around 20–25 years. The quality of the lay and curing is the main factor in reaching the upper end.
Is GRP better than EPDM?
Neither is simply better — GRP gives a hard, seamless, walkable finish suited to balconies and visible roofs, while EPDM is a flexible membrane that is quicker and lower-priced to fit. The right one depends on the roof and budget.
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.