Key points
- EPDM usually lasts longest of the three, GRP gives the neatest walkable finish, and torch-on felt has the lowest upfront cost.
- Rain stops work on every system, but GRP is the most sensitive to cold and damp while it cures.
- Liquid-applied systems suit roofs crowded with details, and single-ply suits large commercial roofs.
- Choose by the roof's shape, use and visibility first, then compare cost and lifespan.
What is the difference between EPDM, GRP and torch-on felt?
EPDM is a synthetic rubber sheet bonded to the deck, GRP is glass-fibre matting set in resin and finished with a coloured topcoat, and torch-on felt is two or more layers of reinforced bitumen membrane melted together with a gas torch.
- EPDM rubber is usually laid as one sheet on a domestic roof, with cold-applied adhesive and no flame. Corners and upstands are formed by folding, or with pre-formed pieces and tapes.
- GRP fibreglass is laminated wet onto a rigid board deck, then cures into a hard, jointless shell. Edges are formed with GRP trims bonded into the laminate.
- Torch-on felt builds up a base layer and a mineral-finished cap sheet, and BS 8217 is the code of practice for these membranes. Modern reinforced bitumen membranes are a long way removed from the single-layer felt that gave flat roofs a poor name.
How do EPDM, GRP and felt compare side by side?
Each system wins on some measures and loses on others, as the table shows.
| Factor | EPDM rubber | GRP fibreglass | Torch-on felt |
|---|---|---|---|
| Guide rate per m² (inc VAT) | £65–£115 per m² | £75–£140 per m² | £60–£105 per m² |
| Single garage, sound deck | £1,600–£2,800 | £1,800–£3,250 | £1,500–£2,600 |
| Indicative service life | 25–50 years | 20–40 years | 15–25 years (high-performance longer) |
| Finish | Matt black rubber | Jointless, coloured topcoat | Mineral chippings, usually grey or green |
| Foot traffic | Light maintenance access | Good, with a suitable topcoat | Moderate |
| Naked flame on site | No | No | Yes, under hot-works controls |
| Weather during laying | Dry deck; adhesives need mild conditions | Dry, within the resin's temperature range | Dry deck; tolerates cooler days |
| Ease of repair | Good, with compatible primer and patches | Good, by grinding back and re-laminating | Very good, widely understood |
Prices are guide figures; the fixed price for your roof follows a free survey. Service lives assume a well-specified roof that is looked after.
Which flat roof system lasts longest?
Of the three, EPDM usually has the longest indicative life at 25–50 years, with one BBA assessment stating at least 35 years for a specific product.
GRP follows at 20–40 years and modern torch-on felt at 15–25, with high-performance felt systems lasting longer. In practice the installation matters as much as the product. A perfect membrane on a roof that holds water, or with a poorly dressed upstand, fails early whatever it is made of. Our guide to flat roof lifespan covers what shortens a roof's life.
Which flat roof system gives the best value over its life?
The cheapest roof to buy is not always the cheapest to own: dividing the installed price by the years of service it is likely to give often narrows the gap between systems.
On a single garage, EPDM typically costs only a little more than torch-on felt, at £1,600–£2,800 against £1,500–£2,600, yet its indicative life is considerably longer. GRP costs more again at £1,800–£3,250, which buys a hard, walkable, seam-free finish rather than extra years. Value also depends on how long you expect to own the property, how visible the roof is and whether it will be walked on. On a roof that needs a new deck and insulation, those items cost the same whatever the membrane, so the difference between systems becomes a smaller share of the total.
Which system looks best on a house?
GRP gives the neatest finish when the roof can be seen, because it has no visible seams and the topcoat comes in a range of colours.
EPDM is a flat, matt black and sits well behind a parapet or out of sight on a garage. Torch-on felt has a textured mineral surface that suits many settings but looks more traditional. If the roof is overlooked from upstairs windows, it is worth seeing finished samples of each before deciding.
Can a flat roof be laid in winter or wet weather?
None of the main systems should be laid on a wet deck, so rain stops work on every one of them; the difference is how well each copes with cold.
GRP is the most weather-sensitive. The resin needs to cure within a set temperature range and dry conditions, so a cold, damp spell can delay a GRP roof for days. EPDM adhesives also need mild, dry conditions, though there are products for cooler weather. Torch-on felt is generally the most tolerant of cold days, because heat is applied as the membrane goes down. Our teams cover the open roof with temporary sheeting overnight and plan the strip-out so that no more is opened than can be made watertight before the end of the day.
Which flat roof system suits garages, extensions, dormers and balconies?
EPDM or felt suit simple garage roofs, EPDM or GRP suit extensions, porches and bays, GRP is a strong choice for dormers, and liquid-applied or GRP systems suit balconies; the shape and use of the roof usually decide before cost does.
- Garages: EPDM or torch-on felt are both sensible on simple, rectangular roofs. EPDM gives the longer life; felt the lower price.
- Extensions and kitchen roofs: EPDM or GRP over a warm-roof build-up, chosen by appearance, rooflights and whether the roof is overlooked.
- Dormers: GRP is often chosen because it forms crisp edges and handles tight cheeks and small areas well. Scaffold is normally needed whatever the system.
- Porches and bays: EPDM or GRP, both of which deal neatly with small, fiddly shapes.
- Balconies and terraces: liquid-applied or GRP where people will walk, often with a protective surface on top. A balcony usually needs planning permission; see our planning guide.
Where do liquid-applied and single-ply roofs fit?
Liquid-applied membranes suit roofs crowded with pipes, plant and awkward junctions, and single-ply suits large, simple commercial roofs.
A cold liquid-applied system is brushed or rolled on with a reinforcing fleece, so it flows around details that would need many cut pieces of sheet. It costs £90–£140 per m², and its life varies widely by product, from about 10 to more than 25 years. It can also be applied over some sound existing roofs, after a survey confirms the substrate.
Single-ply PVC, TPO or FPO sheets are joined with hot-air welded seams and cost £90–£145 per m², with indicative lives of 25–35 years or more. They come into their own on commercial roofs, where large sheets and mechanical fixing keep the cost per square metre down.
Which flat roof system is easiest to repair?
Torch-on felt is the easiest to repair, because it is widely understood and new membrane bonds readily to old.
EPDM repairs well when the right primer and patch are used, but generic bitumen products do not stick to rubber and only cause trouble. GRP can be ground back and re-laminated, though matching the colour of a weathered topcoat is hard. Whatever you choose, keep a record of the system and manufacturer, so whoever repairs it later uses compatible materials. See our flat roof repairs page, or compare whole-job costs in the flat roof cost guide and the guide-price tool.
More questions
Is EPDM better than GRP?
Neither is better in every case. EPDM usually lasts longer and copes well with movement, while GRP gives a harder, walkable, coloured finish and handles tight detailing well.
Is torch-on felt safe to use on a house?
Torch-on felt uses a naked flame, so it is laid under hot-works controls, with cold-applied or self-adhesive products used next to combustible materials such as timber eaves. Where those precautions cannot be met, a flame-free system is the safer choice.
Can you walk on an EPDM roof?
Light foot traffic for maintenance is fine, but EPDM is not a walking surface. Where a roof will be used as a terrace, a protected or walkable system should be specified.
Which flat roof is cheapest?
Torch-on felt usually has the lowest upfront price at £60–£105 per m² on a sound deck, compared with £65–£115 per m² for EPDM and £75–£140 per m² for GRP. All are guide prices including VAT.