Choosing between an EPDM, felt or fibreglass flat roof comes down to three things: how long it lasts, what it costs, and how well it copes with a British winter. Whether you are re-covering a garage, a rear extension or a dormer, this guide compares EPDM rubber, built-up felt and GRP fibreglass flat roof systems side by side, with 2026 UK costs per square metre, realistic lifespans, and the situations each one actually suits.
There is no single best flat roof. The right choice depends on the size of the roof, whether anyone will walk on it, your budget, and how long you plan to stay in the house.
The three flat roof systems at a glance
Felt is the traditional option: layers of bitumen-based sheet built up and bonded with heat. EPDM is a synthetic rubber membrane, usually laid as a single large sheet with very few joins. GRP, or glass reinforced plastic, is fibreglass matting laid wet and sealed with resin to form one seamless, rigid surface. All three keep water out; they differ in lifespan, cost and how they behave over the years.
Felt flat roofs (built-up and torch-on)
Modern felt is a world away from the cheap material that gave flat roofs a bad name. Good built-up or torch-on felt uses two or three bonded layers with a mineral top sheet. It is the cheapest option to install, widely understood by every roofer in Kent and beyond, and forgiving on awkward shapes.
The trade-off is lifespan. Felt typically lasts 10 to 20 years, and the seams and edges are where problems usually start. It copes less well with standing water and can blister in strong sun. For a modest budget or a roof you expect to replace within a decade or two, it still makes sense.
EPDM rubber flat roofs
EPDM is a single-ply synthetic rubber membrane, often fitted in one continuous sheet on a domestic roof so there are few or no joins to fail. Established systems such as Firestone RubberCover and IKO membranes are cold-applied, meaning no naked flame near your home during installation.
Durability is the headline. A properly installed EPDM roof commonly lasts 20 to 50 years, resists UV and thermal movement well, and needs very little maintenance. It is an excellent match for garages, sheds, extensions and dormers. The main limitations are appearance, since the finish is a matte rubber rather than a hard surface, and the fact that a good result depends heavily on careful preparation of the deck below.
GRP fibreglass flat roofs
GRP fibreglass gives a hard, seamless, rigid finish that looks smart and can take foot traffic, which makes it popular for balconies, dormers and roofs that double as a walkway. Because it cures into one solid layer, there are no seams to lift.
Fibreglass typically lasts 25 to 40 years when laid by a trained installer in dry conditions. That last point matters: GRP has to be applied to a dry deck in settled, mild weather, so it is harder to fit in a wet British spell. On roofs that flex a lot it can be prone to hairline cracking over time, so a stable, well-built deck is essential.
Flat roof cost compared
As a 2026 UK guide, supplied and fitted, expect roughly:
- Felt: around 40 to 70 pounds per square metre
- EPDM rubber: around 60 to 95 pounds per square metre
- GRP fibreglass: around 70 to 110 pounds per square metre
On a small single garage of around 15 square metres, that translates to a felt roof at the lower end and a fibreglass one at the top. Access, the state of the existing deck, insulation upgrades and any new trims or gutters all move the final figure, so always get itemised quotes rather than a single lump sum.
It is also worth asking whether you are being quoted for a warm roof or a cold roof. A warm roof places the insulation above the deck, keeps the structure warmer and reduces condensation risk, and is increasingly the expected build-up on habitable rooms. It costs a little more but is often the better long-term choice, especially if building regulations require an insulation upgrade anyway.
Lifespan and durability compared
If longevity is your priority, EPDM and GRP are well ahead of felt. EPDM offers the longest potential life with the least upkeep, GRP gives a longer life than felt plus a hard walkable surface, and felt is the shortest lived but the cheapest to renew. GRP may benefit from a fresh top coat after 15 to 20 years to restore its UV protection, while EPDM generally just needs its gutters and outlets kept clear.
Which flat roof should you choose?
For a garage, shed or extension where you want fit-and-forget durability, EPDM is usually the best value over its lifetime. For a balcony, dormer or any roof that will be walked on or seen up close, GRP fibreglass is the stronger choice. If the budget is tight or the building is temporary, quality felt still does the job. And if the deck underneath is soft or damp, fix that first, because no membrane will outlast a rotten deck.
Building regulations and when you need approval
Re-covering a flat roof can fall under building regulations even when it does not need planning permission. As a rule of thumb, if you replace more than a quarter of the roof area you may need to bring the thermal insulation up to current standards, which often means adding insulation as part of the job. A reputable roofer will factor this in and can arrange the notification. You can check the current rules on the Planning Portal, and manufacturer guidance such as IKO sets out the correct build-up for each system. For more home improvement guides, visit the Contemporary Structures homepage.
Frequently asked questions
Which flat roof lasts the longest?
EPDM rubber has the longest potential lifespan, commonly 20 to 50 years when installed well, with very little maintenance. GRP fibreglass typically lasts 25 to 40 years, and felt 10 to 20 years.
Is EPDM or fibreglass better?
It depends on the roof. EPDM is the better value for garages, sheds and extensions you simply want to last. Fibreglass is better where you need a hard, walkable or highly visible surface such as a balcony or dormer, and it can be fitted only in dry, settled weather.
How much does it cost to replace a flat roof?
As a 2026 guide, felt runs about 40 to 70 pounds per square metre supplied and fitted, EPDM about 60 to 95 pounds, and GRP fibreglass about 70 to 110 pounds. The condition of the existing deck, access and insulation work all affect the total.
Can you put a new flat roof over an old one?
Sometimes, but it is rarely wise. Overlaying traps any moisture in the old layers and hides problems in the deck. Stripping back to a sound deck lets the installer check for rot and gives the new membrane the best chance of reaching its full lifespan.
Do you need planning permission for a flat roof?
Replacing a flat roof usually does not need planning permission, but it can trigger building regulations, particularly around insulation if you renew more than a quarter of the area. Check the Planning Portal or ask your roofer to confirm before work starts.
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