When replacing a flat roof on an extension, garage, or outbuilding, two systems dominate the UK residential market: GRP (Glass Reinforced Polyester, commonly known as fibreglass) and EPDM (Ethylene Propylene Diene Monomer, a synthetic rubber). Both are high-quality modern flat roofing systems, but they suit different applications.
What is GRP Flat Roofing?
GRP involves applying layers of fibreglass and resin to form a hard, seamless, watertight surface. It is rigid once cured and is known for its exceptional durability and low maintenance. Typical lifespan: 25–30 years. Comes with a 20-year manufacturer guarantee from quality installers.
What is EPDM Flat Roofing?
EPDM is a synthetic rubber membrane that is bonded to the roof deck. It is highly flexible, making it ideal for roofs with complex shapes or significant thermal movement. Lifespan: 30–50 years when properly installed.
GRP Advantages
GRP is incredibly hard-wearing and resistant to foot traffic. It's ideal for roofs that will be walked on regularly. It's seamless, so there are no joints that can fail. It can also be moulded around complex shapes and upstands.
EPDM Advantages
EPDM is more forgiving of structural movement and temperature fluctuation. It is lighter than GRP, making it suitable for older structures. Repairs are also generally straightforward — a small puncture can be patched without replacing the whole membrane.
Which Should You Choose?
For most domestic flat roofs — extensions, bay roofs, and garages — GRP is our most commonly recommended system due to its durability and clean finish. For large commercial roofs, older structures, or heavily complex shapes, EPDM may be preferable. Our surveyors will advise on the most appropriate system for your specific project.