EPDM vs GRP vs felt: which flat roof is best?
Rubber, fibreglass and felt compared on price, lifespan and where each one works best.
- Free to use
- No obligation
- Local Merthyr roofers
- Reply within 24 hrs
Last updated 27 October 2026
Flat roofs on extensions, garages and dormers are one of the most common jobs in Merthyr Tydfil. There are three main systems, and each has a place.
Side by side
| EPDM rubber | GRP fibreglass | Torch-on felt | |
|---|---|---|---|
| Lifespan | 20–30+ years | 25–30+ years | 15–25 years |
| Joints | None or few | Seamless | Overlapping layers |
| Fitting in winter | Yes, if dry | Needs dry, mild days | Yes, if dry |
| Walking on it | Occasional, with care | Good | Occasional |
| Naked flame needed | No | No | Yes |
| Best for | Garages, extensions, dormers | Complex shapes, balconies | Tight budgets |
For typical prices per m² and by job size, see the flat roof price guide.
EPDM rubber
EPDM is a sheet of synthetic rubber, usually laid in one piece and glued to the deck. It stretches with the building as it heats and cools, copes with frost, and is quick to fit. The weak points are the edges, trims and upstands, so a neat finish there matters more than the brand of rubber.
GRP fibreglass
GRP is a resin and glass-fibre mat laid on boards, then finished with a coloured topcoat. It sets into one hard, seamless sheet that you can walk on and that looks tidy around rooflights and corners. It needs dry, mild weather to cure, so winter jobs may wait for the right day.
Felt
Modern felt is far better than the single-layer felt on old sheds. A three-layer torch-on system with a mineral cap sheet is cheap and reliable for 15–25 years. It needs a naked flame to lay, so the roofer must have hot-works insurance and take care near timber and gutters.
Which should you choose?
For a simple garage or extension roof, EPDM is usually the best value. For a roof with lots of corners or one you need to walk on, GRP. For the lowest upfront price, felt. Whichever you choose, ask what is happening to the deck and insulation underneath, because that decides how long the roof lasts. See our flat roof cost guide for prices and the flat roofing page to get a quote.
More guides
Questions people ask
Which is better for a roof, EPDM or GRP?
Both last 25 years or more when fitted well. EPDM is quicker to fit, copes with movement and cold, and suits simple shapes like garages and extensions. GRP has a hard, seamless finish that copes better with foot traffic and suits roofs with lots of corners, rooflights or a balcony. Price is similar.
Is felt roofing still worth it?
Modern torch-on felt, in three layers with a mineral cap sheet, lasts 15–25 years and is the cheapest to fit. It still suits some roofs, but most homeowners now choose EPDM or GRP for the longer life.
Can you put EPDM over an old felt roof?
It isn’t recommended. EPDM should be bonded to a clean, dry deck such as new OSB3 boards. Laying over old felt can trap moisture and the bond may fail.
Get a free quote from a local roofer
Tell us what needs doing and we’ll pass it to a trusted local roofer, who will contact you within 24 hours to arrange a quote.
- Free to use, with no obligation to go ahead
- Your details go to one local roofer, not a list of firms
- Add photos to get a better first answer
If water is coming in now, choose “Emergency” so your request is marked urgent.