Four materials cover almost every UK flat roof: EPDM rubber, GRP fibreglass, single-ply membrane, and felt. There is no single best choice. The right one depends on the roof’s size, its use, and how it is detailed at the edges.
The main flat roof materials
EPDM rubber is one flexible synthetic sheet with almost no seams. GRP fibreglass is a rigid, seamless laminate, laid wet and cured hard. Single-ply membrane uses larger welded sheets, common on bigger roofs. Felt is layered bitumen sheets, and our roofing felt guide covers it in full.
EPDM rubber — pros and cons
EPDM goes down as one continuous sheet, so it is quick to fit and copes well with UK weather cycling. It expands and contracts through temperature swings without splitting, which makes it excellent on garages, extensions and dormers.
The material itself is durable when properly cured. Its real weak point is installation, since a poorly bonded seam or edge detail is where most EPDM failures start. Sharp objects or heavy foot traffic in one spot can also puncture it.
GRP fibreglass — pros and cons
GRP cures into a rigid, fully bonded surface with no seams at all, which suits balconies and walk-on roofs well. Because it is rigid rather than flexible, GRP can crack if the timber deck beneath it moves.
Deck stability matters more here than with EPDM. It also costs a little more, and the resin mix and weather during installation both affect how long it lasts.
Single-ply — pros and cons
Single-ply membrane sits between EPDM and traditional felt in typical use. Its sheets are larger than EPDM’s and welded, rather than glued, at the joints, which suits bigger flat roof areas well.
Single-ply offers strong durability at a good cost, although fitters specify it less often than EPDM on a single domestic garage.
Felt — pros and cons
Modern high-performance torch-on felt is a legitimate, budget option for small, low-traffic roofs like sheds. See our roofing felt guide for how it is laid and what to expect.
Felt is the cheapest option and the shortest-lived. The old three-layer nailed felt that gave flat roofs a poor reputation is largely obsolete now, since modern torch-on and self-adhesive felts perform far better.
Getting the falls right (why installation quality matters most)
Every flat roof material shares one requirement: correct falls, so water actually reaches an outlet instead of pooling. British Standard BS 6229 sets out the fall a flat roof needs once built. Most flat roof failures trace back to poor falls or edge detailing, not the sheet material itself. That is exactly why a proper roof survey matters before any flat roof job starts, and why a flat roofing specialist rather than a general roofer is worth seeking out. Our what to check with a roof installer guide is worth reading before you sign anything.
Which lasts longest, which costs least
As a rough ranking, felt is cheapest and shortest-lived, at 10 to 20 years depending on grade. Single-ply sits in the middle on both cost and lifespan, at 20 to 25-plus years. EPDM and GRP cost more upfront but last longest, at 25 to 30-plus years, when properly installed. See our roof repair cost guide for realistic UK price ranges by roof size.
For anything bigger than a shed, EPDM or GRP usually pays for itself over the roof’s life, compared with repeated felt replacements. Our flat vs pitched roof guide is worth a read too, if you are still deciding on the roof shape itself. If you are replacing an older corrugated garage roof, rather than choosing a new material, check our asbestos roof removal guide first. Many older flat garage roofs are asbestos cement, not felt.
Roof types compared
See our types of roof guide for how flat roofing compares with pitched coverings across a whole property, not just a garage or extension.
Find Trusted Roofers connects UK homeowners with flat roofing specialists who install EPDM, GRP and single-ply properly. Not every installer treats every material the same way. That includes flat roofers in Northampton and roofers in Swindon and Oxford, plus roofers covering Liverpool. See our flat roofing guide for the full service, tell us about your roof, and we will match you with a roofer covering your postcode.
EPDM vs GRP vs Felt: Best Flat Roof? — FAQs
What is the best material for a flat roof?
There's no single best material for every roof. EPDM suits most garage and extension roofs well, GRP suits walk-on areas like balconies, and felt remains a reasonable budget choice for small, low-stakes structures. The right choice depends on the roof's size, use and detailing, not a universal ranking.
What are the disadvantages of EPDM roofing?
EPDM can be punctured by sharp objects or sustained foot traffic in one spot. Poor-quality adhesive or seam work causes most of its failures, although the material itself is very durable. Installation quality matters enormously.
What are the disadvantages of GRP fibreglass roofing?
GRP is rigid rather than flexible, so it can crack if the deck beneath it moves or flexes. A poor-quality resin mix or application in unsuitable weather can lead to premature cracking. It also costs more than EPDM for a comparable roof.
Is single-ply roofing good?
Single-ply membrane uses welded sheets in a larger format than EPDM. It performs well and is common on bigger flat roofs, extensions and commercial-style buildings, offering a strong balance of durability and cost. Since it's less commonly specified on small domestic jobs than EPDM, ask your roofer whether it suits your project.
How long does each flat roof material last?
As a rough guide, old-style felt lasts 10-15 years and modern high-performance felt lasts up to 20. Single-ply typically runs 20-25+ years. EPDM or GRP can reach 25-30+ years when properly installed on a sound deck with correct falls.
