Fibreglass GRP roofing

GRP is a strong choice for small and medium flat roofs here, over extensions, dormers, garages and porches, because it forms a single seamless skin with no joints for water to find. It is also unforgiving of bad preparation. The deck underneath has to be sound, dry and rigid, which on most jobs means stripping the old felt and laying a new board deck rather than going over whatever is there, because any movement in the deck will crack the laminate. Falls matter just as much. A flat roof is never truly flat: it needs a fall to an outlet or gutter, and water that ponds on a GRP roof shortens its life, so where the existing roof holds water we set new firrings to correct it before decking. The laminate itself is laid as resin and glass mat, rolled out to drive out the air, with the edge trims, drip trims and upstands bonded into the same skin so the edges are part of the roof rather than stuck onto it. Then a topcoat that protects it from sunlight. The one thing nobody controls is weather: resin will not cure in rain or on a damp deck, so GRP is laid on dry days and covered at the end of each one. We would rather move a day than laminate onto a wet board.

Where the roof meets the wall

Most flat roof leaks are not in the middle of the roof but at the upstand where it meets the house wall. We take the GRP up the wall, then cut a chase and fit a lead or GRP flashing over it, so rain running down the wall cannot get behind the upstand.