GRP (glass reinforced plastic) fibreglass roofing is a flat roofing system made from layers of resin and glass fibre matting, built up and cured to form a single, rigid, seamless surface. Once cured, it’s strong enough to take light foot traffic, making it a popular choice for roof terraces, balconies and dormer roofs.
What does GRP stand for?
GRP stands for glass reinforced plastic, sometimes just called fibreglass roofing. It’s the same family of material used in boat hulls and car body panels, chosen for roofing because once it cures it forms an extremely tough, rigid, waterproof surface.
How is a GRP roof different from EPDM or felt?
The key difference is how the waterproof layer forms. EPDM and felt are both applied as sheets or rolls laid across the roof. GRP is different: it’s built up wet, in layers, directly on the roof, and cures in place to become one solid, seamless surface rather than a laid material. There are no joints or seams at all once it’s fully cured, since the whole roof becomes a single continuous shell.
This rigidity is what makes GRP well suited to roofs that need to take some weight, such as terraces or balconies, in a way that softer membrane materials aren’t designed for.
Can you walk on a fibreglass roof?
Yes, GRP roofing is designed to cope with light foot traffic, which is one of its main advantages over EPDM and felt. It’s a good option for occasional access such as a roof terrace, balcony or maintenance walkway. It isn’t intended for heavy or constant foot traffic, such as regular furniture or continuous use as a living space, so it’s worth discussing exactly how the roof will be used before choosing GRP.
How is a GRP roof installed?
A GRP roof is built up in layers directly on the roof deck rather than laid as a pre-made sheet:
- The roof deck is prepared, cleared of any old roofing material, and checked to make sure it’s completely dry.
- Timber boards are laid and secured, with fixing trims fitted around the edges.
- A layer of resin is applied, followed by the fibreglass matting, which is worked through with more resin to remove air bubbles and bond it fully to the deck.
- Once cured, a protective topcoat is applied to seal and finish the roof.
The roof is usually firm to the touch within an hour or so, though full curing can take a few days depending on the weather. It’s not installed in rain, and needs a moderate temperature to cure properly, too hot or too cold and the resin won’t set as intended, which is why timing installation around the weather matters.
Is GRP roofing durable?
Yes. A professionally installed GRP roof carries a 25+ year lifespan, and with regular maintenance can last considerably longer. Its seamless construction removes the joints that are usually the weak point on other flat roof types, and its rigidity means it resists impact and weathering well. It’s also a strong option for roofs with more complex shapes, upstands or detailing, since the resin can be worked around awkward features in a way that rigid sheet materials can’t. If damage does occur, repairs are usually straightforward rather than requiring the whole roof to be replaced.
Is GRP right for your roof?
GRP tends to suit roofs that need to take some foot traffic, such as terraces, balconies and dormer roofs, or roofs with a lot of detailing where a moulded, seamless finish works better than a laid sheet material.