Ask three roofers for the best flat roof covering and you may hear three answers, each with a good reason. The honest position is that EPDM, GRP and felt all work when they are laid on a sound deck, to a proper fall, by someone who has done it before. They fail for different reasons and cost different amounts, so the choice comes down to the roof in front of you: its size, its shape, how often anyone walks on it and what is attached to it.
This post compares the three coverings people usually choose for a house, a garage or an extension. EPDM is a synthetic rubber sheet. GRP is glass-reinforced plastic, a resin and fibreglass shell sometimes called fibreglass roofing. Felt, or built-up roofing, is bitumen sheet laid in layers, and torch-on felt is the version that is heat-bonded in place. Commercial single-ply membranes (PVC and TPO) get a section of their own. Lifespans and costs come from named guides with the date, and where two sources disagree, we give both. Every price is a typical UK range.
Why there is no single best material
People searching for the best flat roof material usually want a single word. The trouble is that the covering is only part of the roof. A flat roof is a deck, a layer of insulation, a waterproof covering, and the trims and drainage around the edges. A first-rate membrane on a deck that has sagged will still hold water. A modest one on a well-built deck can last for years, and that is why the deck gets as much attention at a survey as the covering.
What decides which material suits your roof?
Five factors do most of the deciding. The first is the shape: a simple rectangle is easy for any material, while a roof with many upstands, rooflights or curves favours a liquid or moulded system. The second is use. A roof that will become a terrace or a balcony needs a surface that tolerates feet and furniture. The third is access, because a sheet material is rolled out and a liquid one is brushed on in the place. The fourth is the condition of the deck, which may need replacing. The fifth is budget, which includes the work to the deck and the edge trims, not just the covering.
Does the fall matter whichever you pick?
Yes. BS 6229:2025 sets a minimum 1:80 finished fall on flat roofs with flexible waterproof coverings, and a roof should be designed to a steeper fall of 1:40, so that it still drains once the deck settles. No material makes up for water that has nowhere to go. Our post on flat roof ponding explains what happens when the fall is wrong.
EPDM rubber: one sheet, few seams
EPDM is a synthetic rubber, and on a domestic roof it is normally supplied as a single large sheet cut to the roof, bonded to the deck with adhesive and finished with trims. Because a small roof can often be covered with one sheet, there are few joints to leak.
How long does EPDM last?
The sources disagree, and it is better to say so. GreenSpec gives an expected service life of 20 to 30 years. Less, in a guide updated on 26 October 2026, says 30 to 50 years. Both are typical ranges and neither is a promise. How the roof is detailed at the edges and around penetrations matters as much as the sheet itself.
What are its strengths and weak points?
It copes with light foot traffic, such as someone stepping out to clear a gutter, though a roof used as a terrace needs protective tiles or decking. It is flexible, which helps on roofs that move with the seasons. Damage is usually repaired with a patch bonded over the spot, and the sheet can be punctured by sharp objects or by a branch dropped on it. Where two sheets meet, the joint relies on tape and adhesive that depend on a clean surface.
What does it cost?
MyJobQuote's rubber roofing guide (October 2026) put rubber at around £60 per square metre, a typical UK number, and an average rubber roof at £1,050 installed. The final cost depends on the roof's area, its edges and the deck beneath. See our page on EPDM rubber roof installation for the way we survey one.
GRP fibreglass: a hard shell
GRP is built in place. The installer lays glass-fibre matting over the deck, saturates it with resin, adds a topcoat, and the result sets into a continuous shell with no joints in the field of the roof. It is a good answer for a roof with awkward shapes and upstands, because the material follows the details.
How long does GRP last?
Less gives 25 to 40 years for GRP (October 2026). As with the other coverings, that range assumes good workmanship, a sound deck and sensible care, and not just the product. The topcoat is the layer you see wear first, and it can be refreshed without stripping the shell below, which is one reason a well-laid GRP roof can outlast its first finish.
Why does GRP crack?
The shell is rigid. If the deck moves, perhaps because boards flex or the building settles, the GRP can craze or split along a joint in the deck. Movement joints at the edges and careful board fixing reduce the risk. Our answer on a GRP roof cracking explains what it looks like and what a repair involves.
Can you walk on it?
The hard surface is among the most foot-friendly of the three, which is why it is often chosen for balconies and roof terraces. Repairs are made by cutting back to sound material and laying new matting and resin. The weather must be dry and not too cold when it is laid, because the resin needs to cure.
What does it cost?
For GRP, what moves the price is the roof area, the number of upstands and rooflights, the state of the deck and how the edges are trimmed.
Torch-on felt: the layered option
Felt, or built-up roofing, is bitumen sheet laid in layers. On a modern roof, torch-on felt is bonded by heating the underside of the roll with a gas torch, and a cap sheet with a mineral surface goes on top. It has been used for a very long time, and a reasonable repair is something most flat roofers can do.
How long does felt last?
Less puts felt at 10 to 20 years, and says a felt roof laid properly can reach 20 years whereas a poorly laid one may fail in under 10. That gap between good and poor is wider than for the other coverings, because so much depends on laying: the laps, the edge details and how the layers are bonded.
What goes wrong with felt?
Felt can blister where moisture has been trapped, split at laps or crack at the edges as it ages. Heating bitumen near timber and roof edges needs care, so the installer's method counts. Blistering is the sign to watch for in the first few years.
What does it cost?
MyJobQuote's felt roof guide (October 2026) gave an average of around £1,500, and £1,200 to £1,800 for a 15 square metre garage roof in SBS felt, a rubberised bitumen type. Felt is often the lowest-cost of the three for a small roof, but a shorter life can change the sums over time. A felt roof replaced twice in the time an EPDM roof lasts once is not the cheaper choice, so work out the cost across the life as well as on day one. A cap sheet in a lighter colour or with a mineral finish also lasts better in sun than a plain black surface, and the installer can tell you what is in the system.
Where single-ply membranes fit
PVC and TPO are single-ply membranes, meaning a factory-made sheet of plastic, or a plastic and rubber blend, joined at its seams by hot-air welding. TPO stands for thermoplastic olefin, and PVC is polyvinyl chloride. They are made for large roof areas, and they appear more often on commercial buildings than on houses.
Why are they less usual on a house?
Welded single-ply suits big, simple roofs, where long runs of sheet can be rolled out and the welding done quickly. A small domestic roof with a dormer and a chimney has so many details that the work becomes mostly hand-finishing, and an installer may reach for EPDM, GRP or felt instead. That is a matter of what suits the job, not a verdict on the materials. On a small roof the welding machine and the crew's set-up time can outweigh the saving from a quick install, and a roof with many corners turns each weld into a hand job.
What about shops and farm buildings?
For a shop, a unit or a farm building with a large flat or low-pitched area, a single-ply membrane may well be the right answer. Our commercial roofing page covers that work, and the survey decides the system. For single-ply, the area, the insulation and the fixing method set the price.
Is any of this regulated?
BS 6229:2025 applies to flat roofs finished with continuously supported flexible waterproof coverings, which includes membranes of this kind, but not lead. If you are changing the build-up, ask your building control body whether the work needs approval. In Taunton that is Somerset Building Control, on 0300 303 7790.
The three compared side by side
The table puts the domestic options next to each other. The lifespans are typical ranges from named guides and are not promises. The costs are typical UK figures from those guides and are not our prices. Where a cell says Set after survey, that means the roof's own details settle the price.
| Covering | Typical life | Foot traffic | Repairs | Cost guide |
|---|---|---|---|---|
| EPDM | 20 to 30 years (GreenSpec); 30 to 50 years (Less) | Light, with protection for more | Bonded patches | Around £60 per m2; average £1,050 (MyJobQuote, Oct 2026) |
| GRP | 25 to 40 years (Less) | Hard-wearing; suits walkways | Cut back and relay | Set after survey |
| Torch-on felt | 10 to 20 years (Less) | Light; edges need care | Patches and cap sheet | Average around £1,500 (MyJobQuote, Oct 2026) |
What does a whole replacement cost?
MyJobQuote's flat roof guide (October 2026) gave £1,500 to £6,000 for a replacement, with an average of £2,400. For a 15 square metre garage, Less gave £1,200 to £2,500. Check any quote for VAT, deck repairs and the edge trims.
So which should you choose?
Bring the roof's use and shape to the survey, and be ready to say whether you ever expect to put a roof light, solar panels or a terrace on it. If it is a simple shape and rarely walked on, EPDM is a strong candidate. A terrace or complicated shape favours GRP. A small, low-cost job where you accept a shorter life might suit felt. Our flat roofing page explains how we survey and quote.
Flat roof material questions
Which flat roof covering lasts longest?
The published ranges overlap, so no covering wins outright. EPDM is given as 20 to 30 years by GreenSpec and 30 to 50 by Less, GRP as 25 to 40 years and felt as 10 to 20 years by Less. Workmanship, the deck and the fall change the real figure for any of them.
Is EPDM or GRP better for a roof terrace?
GRP's hard surface is often picked where people will walk regularly, although it can crack if the deck moves. EPDM can take a terrace too, but it needs protective tiles or decking over it. The roof's shape, the deck and how you will use it decide, so ask for both options to be considered at the survey.
Can I put a new covering over the old flat roof?
Sometimes, but not always. A new covering can only be laid over old material that is dry, sound and flat, and the new build-up may have to meet Building Regulations. A survey checks for trapped moisture and a failed deck, and the answer is often to strip back to the deck and look at what lies underneath.
More on this subject: Flat roofing in Taunton
