EPDM vs GRP Fibreglass: Which Flat Roof System is Right for You?

If you're having a new flat roof installed, you'll likely be choosing between EPDM rubber and GRP fibreglass. Both are excellent modern systems that far outperform traditional felt, but they have different strengths depending on your project.

What is EPDM?

EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber membrane. It's flexible, lightweight, and comes in large sheets that can cover a whole roof with minimal joins — which means fewer potential leak points. EPDM is particularly good for complex roofs with unusual shapes, and it performs excellently in the UK climate.

What is GRP Fibreglass?

GRP (Glass Reinforced Plastic) fibreglass roofing is a rigid, seamless system applied in liquid form and then cured. It bonds directly to the roof deck and creates an incredibly durable, waterproof surface. GRP is common on domestic extensions and is popular for its clean, professional appearance.

Key Differences

• Flexibility: EPDM is more flexible and better for complex shapes; GRP is rigid
• Joins: EPDM has very few joins; GRP is seamless
• Appearance: GRP can be finished in any colour and looks very neat
• Cost: Both are similarly priced for most domestic projects
• Lifespan: Both offer 30+ years with proper installation and maintenance
• Repairability: EPDM is easier to patch repair; GRP repairs can be more visible

Which Should You Choose?

For a simple flat roof on an extension, GRP fibreglass is often the preferred choice — it's extremely durable and gives a high-quality finish. For larger or more complex commercial roofs, EPDM is frequently the better option due to its flexibility and large sheet sizes.

Our team can advise which system best suits your specific project. Contact us for a free survey and quote.