Flat Roofing Materials Compared: Felt, EPDM, GRP and Liquid
You have already decided on a flat roof — now you need to pick the material. This is the decision that determines whether your roof lasts 10 years or 40. Traditional felt is still the cheapest option but it is increasingly hard to justify when EPDM rubber and GRP fibreglass offer double or triple the lifespan for 30 to 50 percent more money. Liquid-applied systems fill a niche for complex shapes. This guide is a deep-dive comparison of all four systems: costs per square metre, real-world lifespan, installation requirements and where each one makes sense. If you are still deciding between flat and pitched, start with our flat vs pitched roof comparison first.
Torch-On Felt
Modified bitumen felt applied with a gas torch in two or three layers. This is the traditional flat roofing method and still accounts for a large share of installations.
- Cost - £40 to £60 per square metre installed.
- Lifespan - 10 to 20 years for a three-layer system. Single-layer budget jobs may fail in under 10 years.
- Pros - Lowest upfront cost, widely available, most roofers can install it, proven technology.
- Cons - Shortest lifespan of any option, joints are the weak point, fire risk during installation (open flame), prone to cracking in extreme cold, multiple layers add weight.
Felt is still a reasonable choice for sheds, garages and budget repairs where longevity is not the priority. For anything else, EPDM or GRP are better long-term investments.
EPDM Rubber Membrane
EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane laid in a single sheet. Firestone RubberCover and ClassicBond are the most common brands in the UK.
- Cost - £60 to £90 per square metre installed.
- Lifespan - 30 to 50 years. Many manufacturers offer 20-year guarantees as standard.
- Pros - Excellent lifespan, very flexible (accommodates building movement), UV resistant, can be laid in large single sheets (reducing joints), environmentally friendly.
- Cons - Black appearance is not to everyone's taste, detailing at edges and upstands requires skill, not as rigid as GRP (can look slightly wrinkled on larger roofs).
EPDM is arguably the best all-round flat roofing material available today. The combination of longevity, flexibility and relatively straightforward installation makes it hard to beat for most domestic applications.
GRP Fibreglass
GRP (glass reinforced polyester) creates a seamless, rigid shell over the roof surface. It is applied as layers of resin and chopped strand mat, then finished with a topcoat.
- Cost - £80 to £110 per square metre installed.
- Lifespan - 25 to 30 years, sometimes longer with good maintenance.
- Pros - Completely seamless finish (no joints to fail), very strong, can be walked on, available in various colours, easy to repair if damaged.
- Cons - More expensive than EPDM, rigid (can crack if the building moves significantly), temperature sensitive during installation (cannot be laid in very cold or very hot conditions), strong smell during application.
GRP is excellent for balconies, walkways and roofs where you need to walk regularly. The seamless finish looks very clean and professional. However, it is less forgiving of structural movement than EPDM.
Liquid Applied Waterproofing
Liquid systems use a cold-applied resin or polyurethane that cures to form a flexible, seamless membrane. Brands like Kemper, Sika Liquid Plastics and Triflex are used across the UK.
- Cost - £70 to £120 per square metre installed.
- Lifespan - 20 to 25 years depending on the product and number of coats.
- Pros - Seamless, can coat complex shapes and details easily, cold applied (no naked flames), can often be applied over existing coverings, good for repairs and overlays.
- Cons - Sensitive to moisture during application (surface must be completely dry), costs add up on larger areas, quality depends heavily on applicator skill, some products have strong odour.
Liquid systems really come into their own for complex roofs with lots of details, upstands, pipes and awkward shapes. They are also popular for refurbishment work where stripping the old covering is impractical. For simple rectangular roofs, EPDM or GRP usually offer better value. Whichever system you choose, regular maintenance and drainage checks are essential to reach the material's full lifespan. For total project costs including labour, see our roof replacement cost guide.
Frequently asked questions
Which flat roofing material lasts the longest?
EPDM rubber has the longest expected lifespan at 30 to 50 years. GRP fibreglass comes second at 25 to 30 years. Both significantly outlast traditional felt, which typically manages 10 to 20 years.
Can I install EPDM or GRP myself?
EPDM is more DIY-friendly than GRP, and some suppliers sell kits for smaller roofs. However, the detailing at edges, upstands and outlets is where problems occur, and this is where professional experience makes the difference. Most manufacturer guarantees are only valid when the product is installed by an approved contractor.
What causes flat roofs to fail?
The most common causes are poor installation (especially at joints and edges), ponding water due to inadequate falls, foot traffic damage and thermal movement cracking the membrane. Regular inspection and keeping drainage outlets clear prevents most problems.