How Long Does a GRP Roof Last?

GRP, or glass-reinforced plastic, is a one-piece shell made from resin and glass matting, with a coloured topcoat on the outside. Because there are no laps and no seams to peel, it has a good reputation among flat roofs. The figure published by Less, in a page last updated in March 2026, is 25 to 40 years for GRP, against 10 to 20 for felt.

That is a typical range for roofs laid and looked after properly, not a guarantee. A warranty from an installer is a separate matter and says nothing about how long the material will last. Some roofs reach the top of the range with only the odd topcoat; others show faults inside ten years because the build was poor.

It helps to think of the roof as three parts. The deck gives it a stable base, the laminate keeps the water out, and the trims and upstands manage the edges. A fault in any one of them can end the roof's life well before the laminate itself has worn out. When people ask how long a GRP roof lasts, they are often really asking how well theirs was built.

Thin laminate is the commonest cause. A roof with one light layer of matting has little strength in reserve, so it crazes and cracks under sun, frost and foot traffic. A thicker build, with matting laid in more than one layer and given enough resin, flexes without splitting.

Poor trims come next. The edge trim, which carries water into the gutter, and the upstand that turns up beside a house wall are the points that take the most movement. If they are screwed to weak timber or are not sealed along the underside, wind and thermal movement open them up. Our page on a flat roof edge trim leaking explains how that begins.

A wet deck is another. If the plywood is not fully dry when the laminate goes down, moisture is sealed inside and causes blistering and rot. Standing water does harm as well, because the roof carries a constant load and the topcoat degrades faster beneath it. A roof laid without a proper fall will gather puddles. Last, rough use shortens life: sharp furniture feet, dragged planters and heavy foot traffic all scratch and thin the surface.

GRP ages slowly, so the early signs are easy to miss. The topcoat fades and turns chalky as ultraviolet light breaks down the resin. A web of fine lines across the surface, called crazing, shows the gel coat is losing flexibility. White patches where glass fibre shows through suggest the topcoat has worn away in places and the matting is exposed.

Further along, cracks start to follow the deck joints, corners and trims. A crack that goes right through to the matting can let water reach the deck, and a soft, spongy feel underfoot means the board beneath has taken in moisture. Dark stains on the ceiling below, or damp that returns after a repair, tell you water is already inside.

A fresh topcoat can extend a sound roof that has only faded or crazed on the surface, so catch it early. If cracks are wide and spread across the roof, our answer on why a GRP roof cracks covers the causes and the repairs that hold. Look from a window or ladder first, and step out only if the surface feels firm.

Simple upkeep adds years. Keep the surface clear of leaves, moss and debris, and make sure the outlet or gutter runs freely. Wash off dirt with a soft brush and clean water rather than a pressure jet, which can lift edges. Look over the trims and joints after storms, and have small cracks sealed early, since a small repair costs far less than a failed deck.

Once a roof is nearing the end, there are two choices: a new topcoat over sound laminate, or replacement. Checkatrade's September 2026 fibreglass guide gives a national guide of £36 per m² for the covering alone, and around £210 per m² fully insulated. Your own figure depends on area, access and the deck, and the single written price follows the survey.

If you are weighing a new GRP surface over old felt, our page on can you put GRP over felt sets out the limits. For the wider picture of coverings, see flat roofing, and for weighing a repair against a new roof see repair or replace a flat roof.