Fibreglass Roof Cost: What Decides the Price

The square metre rate covers the laminate, topcoat and labour on an open, simple area. Small roofs often cost more per square metre than large ones, because setting up, mixing and finishing the edges take a similar amount of time whatever the size. A plain rectangle is the quickest shape to lay; a roof with corners, steps or several levels takes longer.

GRP is well suited to complex shapes because it is laid wet and every trim becomes part of one seamless skin. That is a strength, but each extra detail still adds time, so the shape of your roof matters as much as its size.

Fibreglass needs a firm, dry, sound deck. When the old covering is stripped, the boards are checked. Sound boards stay; soft or rotten ones are replaced, and that adds materials and labour. This is the biggest unknown on many flat roof jobs, which is why a quote should say how deck repairs will be handled if they are found.

GRP should not be laid over old felt. Stripping back to the deck is part of a proper job and should be included in the quotation, along with taking the old covering away.

Drip trims along the edges, upstands where the roof meets a wall, and the outlet or gutter detail are where flat roofs most often fail. GRP trims are bonded into the laminate, and every metre of edge or wall abutment adds work. Rooflights, vent pipes and other penetrations each need detailing too.

If a wall abutment needs new flashing above the upstand, that may be leadwork priced as a separate item. Ask for it to be listed so you can see the difference between the roof covering and the details around it.

Replacing a roof is the natural time to consider a warm roof build-up, with insulation laid above the deck. It adds cost, but it moves the deck to the warm side and reduces condensation risk. Insulation thickness can also change the height of the roof edge, which affects trims and any adjoining windows or doors. Our warm roof versus cold roof guide explains the difference.

Not every cracked or leaking fibreglass roof needs replacing. If the laminate is sound and the fault is local, a compatible repair may be practical, and our fibreglass roof repair page explains when that works. Widespread cracking, a wet deck or repeated failures make replacement the better value.

When comparing quotes, check that each one includes stripping, deck inspection and repair terms, trims, upstands, outlets, insulation if wanted, access and waste. A lower total that leaves out the deck or the trims is not the cheaper roof.