EPDM Rubber vs GRP Fibreglass vs Felt: Flat Roof Materials Compared

When we quote a flat roof, one of the first questions is which material to use. There are really three realistic options in 2026: EPDM rubber, GRP fibreglass, and traditional felt. However, each one has a genuinely different cost and lifespan. Here’s how they compare, without the sales pitch.

EPDM rubber

EPDM is a single sheet of synthetic rubber membrane. Installers bond it down with very few joins, often none at all on a domestic roof. Trade cost guides put fitted pricing at roughly £70–£100 per m², including materials and labour. Lifespan is commonly rated at 30–50 years, when fitted well and left undamaged. Smaller roofs under about 15m² tend to carry a minimum-job premium. That’s because setup and access costs don’t scale down with the roof size. Our full EPDM guide covers this in more depth.

GRP fibreglass

Installers apply GRP as a liquid resin over a fibreglass mat, then finish it with a topcoat. The result is one seamless surface you can walk on. Since it’s seamless and walkable, it’s a common choice for balconies, roof terraces and flat-roofed extensions alike. UK cost guides disagree on installed pricing — from around £70–£110 per m² to £150–£240 per m², depending on what’s included. A typical domestic job commonly lands around £100–£160 per m². Lifespan is typically 20–30 years as a standard installation. Well-maintained or higher-spec, BBA-certified systems can reach 30–40 years or more. The one thing to watch is the conditions on site. GRP needs dry weather and the right temperature to cure properly. A rushed job in cold or damp weather can crack or peel later. See our GRP pros, cons and cost guide for the details.

Felt

Traditional built-up felt is the cheapest option to install, at roughly £40–£60 per m². However, it’s also by far the shortest-lived. Older, basic single-layer felt typically lasts only 10–15 years in UK conditions. A modern three-layer torch-on system, fitted to BS 8217, commonly reaches 20–30 years with a regular check. Felt’s main weaknesses are its seams — every join is a potential failure point. UV exposure is the other, since it makes the material brittle over time. It still has a place on lower-budget or short-term projects. Still, it’s rarely the most economical choice over a 20-plus-year period, once earlier replacement is factored in.

Side-by-side summary

• EPDM: ~£70–£100/m², 30–50 year lifespan, minimal seams, best all-round value for most extensions and garages.
• GRP: ~£100–£160/m² typical (guides range £70–£240/m²), 20–30 year lifespan as standard (30–40+ years for higher-spec systems), walkable and seamless, ideal for balconies and terraces, but installation-condition sensitive.
• Felt: ~£40–£60/m², 10–30 year lifespan depending on system, cheapest upfront, shortest-lived and most seam-prone.

Which one should you choose?

For most domestic flat roofing jobs across our Doncaster coverage area and South Yorkshire, EPDM offers the best balance of cost and longevity. That includes the extensions and garages we quote regularly around Worksop and near Retford. Consequently, it’s become our default recommendation for extensions and garages. GRP earns its place where the roof needs to be walked on, or where a seamless, high-end finish matters. Felt still suits a genuinely tight budget, or a building that doesn’t need its roof to last much longer. Still, we’ll never recommend it as a long-term solution without saying so.

Further reading

If you’re weighing up a flat roof against a traditional pitched design in the first place, our flat vs pitched roof comparison lays out the trade-offs. Similarly, if the rest of the house is tiled, our slate vs concrete roof tiles guide covers the pitched-roof equivalent of this same cost-and-lifespan comparison.

Whichever system suits your roof, we’ll explain why during the survey. We won’t default to whatever’s easiest for us to install.