Flat Roof Materials Compared — EPDM vs GRP vs Felt

Traditional Felt Flat Roofing

Traditional built-up felt has been used on flat roofs in the UK for over a century. It consists of multiple layers of bitumen-impregnated felt bonded together, typically finished with a mineral-surface cap sheet.

Lifespan

10–15 years for quality torch-on systems. Traditional cold-applied felt can fail in under 10 years. Not suitable where longevity is the priority.

Cost

The lowest upfront cost of the three options — typically £40–£60 per m² supplied and fitted. However the shorter lifespan means higher whole-life cost on properties where the roof will be in place for decades.

Performance in Surrey

Felt performs adequately in Surrey conditions but is vulnerable to UV degradation in summer heat and frost cracking in cold winters. The seams and laps are potential weak points that can fail over time.

BS 6229:2018, the British Standard for flat roofs of continuously supported flexible waterproof coverings, requires a minimum finished fall of 1:80 to ensure positive drainage and prevent ponding.Source: BS 6229:2018

EPDM Rubber Flat Roofing

EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane that has been widely used in commercial roofing for decades and is now the material of choice for many residential flat roofs.

Lifespan

20–25 years in practice, with some installations performing for 30+ years. The rubber remains flexible across a wide temperature range, making it resistant to the freeze-thaw cycles that damage felt.

Cost

£50–£80 per m² supplied and fitted. Mid-range initial cost with significantly lower whole-life cost than felt given the longer service interval.

Performance in Surrey

Excellent — EPDM handles both summer UV exposure and winter frost well. The single-ply membrane eliminates the seam vulnerabilities of felt. Best suited to larger flat roof areas where the sheet size advantage is most pronounced.

GRP Fibreglass Flat Roofing

GRP (glass reinforced polyester) is a cold-applied fibreglass system that creates a fully seamless waterproof surface. It's become the dominant premium flat roof material for residential use in the UK over the last 15 years.

Lifespan

25–30 years for a quality installation. The fully seamless surface eliminates the primary failure mechanism of other flat roof systems. GRP roofs installed correctly have very few maintenance requirements.

Cost

£60–£100 per m² supplied and fitted. Highest initial cost of the three but the lowest whole-life cost on most applications given the lifespan and near-zero maintenance.

Performance in Surrey

Outstanding. GRP is UV stable, frost resistant and unaffected by standing water. The seamless application means there are no joints or laps that can fail over time. We recommend GRP as the standard specification for Farnham flat roofs where budget allows.

Which Should You Choose?

For most Farnham homeowners, GRP is the right answer if budget allows — you're paying more upfront to avoid having the same conversation again in 12 years. EPDM is an excellent alternative for larger areas or unusual shapes. Felt makes sense only where the property is being sold, the budget is genuinely constrained, or where the roof area is very small.

The most important factor after material choice is correct installation — particularly adequate drainage falls. A flat roof without proper falls will pond water regardless of the membrane quality, and standing water is the primary cause of premature failure on all flat roof types.

Last reviewed: 19 July 2026