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Waterproofing Explained: What is GRP Roofing?

What does GRP mean?

What does GRP mean?


Glass(fiber) Reinforced Plastic (GRP) is a composite material that consists of a polymer matrix and glass fibers. The polymer matrix is usually an epoxy, vinylester, or polyester thermosetting resin.

Fiberglass sheets are a common type of fiber-reinforced plastic using glass fiber. The fibers may be randomly arranged, flattened into a sheet, or woven into a fabric before being used with a resin/epoxy which hardens. Which results in a strong lightweight product.

It's for this reason GRP is widely used and most commonly used in the marine industry as well as the roofing industry.
What is GRP Roofing?

What is GRP Roofing?


GRP Roofing systems combine a few different materials. This includes the OSB3 decking, the Fiberglass material, resin/epoxy, and the durable topcoat. This mixture of materials when laid correctly creates a strong and robust roofing material. Usually fibreglass preformed trims are added to create a roof directs rainwater to the designed drip edge/gutter.

Fibreglass roofing consists of wetting out layers of fiberglass mat on the roof of the building. When cured, your roof should have strength and provide a continuous waterproof barrier across the whole surface of the roof.

So lets start from the beginning. You have your roof structure with bare ceiling joists, which you would usually attach a quality OSB3 decking (Usually min. 18mm thick) with insulation to help reduce heat loss and create a warm roof. You can install without insulation making a cold roof but do take into account the Part L of Regulations.

GRP edge trims are then fitted to finish the sides, making sure water can then run to the drip edge. GRP Laminate which is made up of the fibreglass material and your resin which you will need to mix yourself can then be laid. Usually a 450 csm (chop strand mat) is the usual for flat roofs that won't have people walking on it, if it's going ot be a terrace then you will need a thicker mat, something like a 600 csm. Once this is all laid, the roof can then be finished with a topcoat. Most suppliers will offer a few different colour choices, usually a dark grey is the standard and most popular topcoat colour but this is persoanl choice as you may want to match it to your windows, doors or skylight. The topcoat then finishes your roof perfectly and your will now have a roof that is extremely strong as well as watertight. Most GRP systems come with a warranty if installed to the correct guidelines or by a specially qualified installer.

So, benefits of GRP Roofing:

  • Easy installation

  • Superior durability/long life

  • No joins or seams like felt

  • Flame-free and safe installation

  • Easy repairs if needed

  • Great finish and aesthetics - Range of colour finishes

  • Can be used with virtually all Flat Roof Windows


  • GRP Roof Edge TrimsAluminium Roof TrimsFlat Roof Edge Trims

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