The short answer
EPDM rubber (£80–£120/m², 20–30 years) and GRP fibreglass (£90–£130/m², 20–30 years) are the two long-life modern flat-roof systems; built-up felt is cheaper up front but typically lasts 10–20 years. EPDM is flexible and laid in large sheets, ideal for simple shapes; GRP gives a hard, seamless finish that suits roofs with foot traffic or rooflights; felt is the budget option. There is no single “best” — the right choice depends on the roof. For costs in detail see our flat roof cost guide.
Most UK flat roofs are covered with one of three systems, and each has a genuine place. This guide compares EPDM rubber, GRP fibreglass and built-up felt on the things that matter — cost, lifespan, finish, and which roofs they suit — so you can read a quote with an informed eye. All figures are typical illustrations, not quotes.
The three systems at a glance
- EPDM rubber £80–£120/m² · 20–30 yrs
- GRP fibreglass £90–£130/m² · 20–30 yrs
- Built-up felt cheaper · 10–20 yrs
- Best for simple shapes EPDM
- Best for foot traffic / hard finish GRP
- Best for tight budget Felt
EPDM rubber
EPDM is a synthetic rubber membrane, usually laid as a single large sheet bonded to the deck, with very few or no joints on a small roof. That single-piece nature is its great strength — fewer seams mean fewer places to fail — and it stays flexible across temperature swings, so it copes well with movement. It is well suited to garages, extensions and simple rectangular roofs. The finish is matt black and slightly soft underfoot, so it is less suited to roofs with regular foot traffic or where a hard, walkable surface is wanted. Typical life is 20–30 years; see our lifespan guide.
GRP fibreglass
GRP (glass-reinforced plastic) is built up in place from resin and glass matting, then top-coated, producing a seamless, hard, durable surface. It bonds tightly to the deck and handles complex shapes, upstands and rooflights well, and the hard finish takes foot traffic, making it a good choice for balcony-style roofs or where rooflights are involved. Its main demands are on installation: it must be laid in dry, suitable weather by a skilled installer, and a poor lay can craze or delaminate. Typical life is 20–30 years.
| Factor | EPDM rubber | GRP fibreglass | Built-up felt |
|---|---|---|---|
| Typical cost | £80–£120/m² | £90–£130/m² | cheaper |
| Lifespan | 20–30 yrs | 20–30 yrs | 10–20 yrs |
| Joints | Few / none | Seamless | Layered/lapped |
| Foot traffic | Limited | Good | Limited |
| Best for | Simple shapes | Complex / walkable | Tight budgets |
Built-up felt
Built-up felt (often called “torch-on” for modern systems) layers bitumen sheets to form the waterproof covering. It is the most economical option and modern high-performance felts are far better than the short-lived felt of the past, but it still typically lasts less than rubber or fibreglass — 10–20 years — and the lapped joints are the usual point of eventual failure. It remains a reasonable choice on a tight budget or for a roof not expected to be permanent.
Which should you choose?
For a simple garage or extension roof on a long-term home, EPDM or GRP are the sensible choices — EPDM where the shape is simple and budget matters slightly more, GRP where the roof is complex, walkable or has rooflights. Felt suits tight budgets or short-horizon roofs. Whatever the material, the deck must be sound and, on a renewal, Building Regulations may call for a warm-roof insulation upgrade — see our insulation and ventilation guide. To decide whether your current roof needs renewing at all, see repair or replace.
Compare flat roof quotes
The right material depends on your roof. Compare itemised quotes from vetted roofing contractors who can advise on the best system for your situation.
Frequently asked questions
Which is better, EPDM or fibreglass?
Neither is universally better. EPDM rubber is flexible, laid in large sheets with few joints, and ideal for simple shapes; GRP fibreglass gives a hard, seamless, walkable finish that suits complex roofs and rooflights. Both typically last 20–30 years. The right choice depends on the roof shape, use and budget.
How long does each flat roof material last?
EPDM rubber and GRP fibreglass both typically last 20–30 years. Built-up felt typically lasts 10–20 years. Lifespan in practice depends heavily on installation quality, drainage and the condition of the deck beneath.
Is felt still worth using on a flat roof?
Modern high-performance felt is far better than older felt and remains a reasonable budget choice, but it still typically lasts less than rubber or fibreglass, and its lapped joints are the usual eventual failure point. For a long-term roof, EPDM or GRP are usually the better value over time.
Can I walk on a flat roof?
It depends on the system. GRP fibreglass gives a hard surface that takes foot traffic well; EPDM and felt are softer and better suited to occasional access only. If the roof is meant to be a usable terrace, tell the roofer so the right walkable build-up is specified.
Sources & further reading
- NFRC (National Federation of Roofing Contractors) — flat roofing systems and standards
- CompetentRoofer — flat-roof self-certification under Building Regulations
- Manufacturer technical guidance — EPDM, GRP and built-up felt system specifications
This is general information, not advice for your specific property or roof. The right system varies with your roof shape, use, budget and chosen contractor. Flat roof work should be carried out by a vetted roofing contractor.