GRP vs EPDM Flat Roofs: Pros and Cons

Published 1 April 2026 • By High and Dry Roofing

If you are replacing a flat roof, you will likely be choosing between two modern systems: GRP (glass reinforced polyester, commonly known as fibreglass) and EPDM (ethylene propylene diene monomer, a type of synthetic rubber). Both are significant improvements over traditional felt, but they have different strengths and suit different situations. Here is how they compare.

GRP Fibreglass Flat Roofs

GRP is applied as a liquid resin with a fibreglass mat, which cures to form a single, seamless, rigid surface. It has become one of the most popular flat roofing systems in the UK.

Pros

• Completely seamless: No joints or seams means no weak points where water can get in.
• Very durable: The rigid surface resists impact, foot traffic and UV damage well.
• Long lifespan: Typically 25-30 years with minimal maintenance.
• Walkable surface: GRP creates a firm, non-slip finish that can be walked on safely, making it ideal for balconies and roof terraces.
• Wide range of finishes: Available in different colours and can include a non-slip aggregate finish.

Cons

• Higher cost: GRP is generally more expensive than EPDM to supply and install.
• Weather-dependent installation: GRP resin should not be applied in very cold, wet or humid conditions, which can sometimes cause delays.
• Not ideal for very large areas: On larger roofs, the rigid nature of GRP can be a disadvantage as it does not flex with building movement.
• Specialist installation: Must be installed by an experienced fibreglass roofer to avoid problems.

EPDM Rubber Flat Roofs

EPDM is a single-ply rubber membrane that is rolled out and bonded to the roof deck. It has been used in commercial roofing for decades and is increasingly popular for domestic flat roofs.

Pros

• Excellent flexibility: EPDM stretches and flexes with building movement, making it less prone to cracking.
• Very long lifespan: High-quality EPDM can last 25-50 years.
• Lower cost: Generally cheaper to supply and install than GRP.
• Suitable for large areas: Available in large sheets, reducing the number of seams needed on bigger roofs.
• All-weather installation: Can be installed in a wider range of weather conditions than GRP.
• Lightweight: Places less structural load on the building than GRP.

Cons

• Seams on larger roofs: If the roof is larger than the membrane sheet, seams are needed which are potential weak points.
• Less resistant to foot traffic: EPDM can be punctured by sharp objects and is less suitable for areas that are regularly walked on.
• Limited colour options: Typically only available in black or dark grey.

Which Should You Choose?

For smaller flat roofs such as porches, bay windows, garages and single-storey extensions, GRP is often the better choice due to its seamless finish and durability. For larger flat roofs, or where budget is a primary concern, EPDM can be the smarter option. Both systems are vastly superior to traditional felt and will provide decades of reliable, leak-free performance when installed correctly.

At High and Dry Roofing, we install both GRP and EPDM flat roofing systems and can advise on the best option for your specific project. We are happy to visit your property, assess the roof and provide a detailed quote for both options so you can make an informed decision.