How a GRP roof is built
GRP is made on the roof itself. The deck, normally new OSB or similar boarding, has to be dry, firm and fixed so it won't move. Edge trims go on first. Resin is then rolled into a chopped-strand glass mat laid over the boards, bubbles are worked out, and the laminate is left to cure. A topcoat goes on afterwards to protect the laminate from sunlight and give the finished colour.
Because the material starts as a liquid, it can be carried up walls, around rooflights and into corners as one continuous layer. That's its biggest strength: there are no lapped seams for water to find.
Where fibreglass suits best
- Balconies and roofs that will be walked on, with a textured topcoat.
- Small roofs with lots of corners, such as dormers and bay tops.
- Roofs where a crisp, smooth finish matters because it's overlooked.
- Porch and canopy roofs where tidy edges are on show at the front door.
It is less forgiving on large roofs over decks that flex, or on buildings likely to move, where a flexible membrane may cope better. We compare the two honestly on our EPDM rubber roofs page.
Weather and timing
Resin needs dry conditions and sensible temperatures to cure properly. Damp boards or a shower at the wrong moment can spoil the bond, so a GRP job is planned around a settled spell. That can mean waiting a few days in a wet Somerset autumn, which is better than a laminate that delaminates later.
GRP roof repair
Fibreglass roofs most often fail at the edges, where the laminate meets a trim and movement opens a fine crack. Other faults include crazing in the topcoat, impact damage and blisters where moisture was trapped during laying. A GRP roof repair grinds out the damage, feathers the edges, lays new mat and resin over the area and finishes with topcoat. If water has already rotted the boards underneath, the repair has to include that section of deck. Our general flat roof repair page covers other systems too.
Asking a GRP roof specialist the right questions
When comparing local fibreglass roofers, ask what deck they'll lay onto, which trims they'll use, how they deal with the wall junction and what happens if rain is forecast. The answers tell you more than any brochure. Costs depend on size, access, deck condition and detailing; our flat roof cost guide explains each factor without guesswork figures.
The deck and the finish are one system
A fibreglass roof is not just a painted finish. The supporting boards, their joints, the laminate and the trims have to work together. If the base moves too much, a hard surface may crack even though the topcoat still looks tidy. Ask whether existing boards can be retained and what preparation is proposed before comparing an overlay with a replacement. A visible crack at a trim needs its cause considered, not simply another coat applied over the line.
Rooflights and wall upstands also affect the specification. Their position determines where reinforcement and finishing details are needed, while the outlet determines how rain leaves the roof. Include a photograph from a window showing those features when enquiring. That provides useful context without requiring you to stand on the surface. For a roof intended as a walkway, make its intended use clear: a hard coating alone does not establish that the underlying structure is designed to carry people.
Book a look
We lay and repair GRP roofs on homes and commercial buildings across Somerset and Devon, within about 50 miles of Taunton. Call 07399 680142 or send your details for a free written quote, or see all our flat roof options.