The short answer
On published lifespans neither system wins clearly. One cost guide puts GRP at 25 to 40 years, and EPDM is quoted anywhere from 20 to 30 years or more, to 30 to 50 years in another source. EPDM tends to cost slightly less per m² and flexes with movement, while GRP gives a hard, walkable surface. A well laid roof of either kind, with sound falls and neat detailing, can reach the top of its range.
How long EPDM and GRP are quoted to last
The two systems are built differently. EPDM (ethylene propylene diene monomer) is a rubber sheet rolled out and fixed to the roof. GRP means glass-reinforced plastic, often called fibreglass: liquid resin and glass matting are worked on in place and harden into a skin. Their quoted lives overlap.
| System | Typical life quoted | Source |
|---|---|---|
| EPDM | 20 to 30 years | GreenSpec |
| EPDM | In excess of 25 years | Building Centre, 2017 |
| EPDM | 30 to 50 years | Less, 2026 |
| GRP | 25 to 40 years | Less, 2026 |
The sources differ in age and method, which explains much of the spread: one is a trade body, another a materials database and others are cost guides, each with its own way of measuring a roof that is still in service. Treat the figures as typical ranges, not a promise. Manufacturer warranties on EPDM are commonly 20 to 25 years, but a warranty describes the product's conditions, not how long the roof will last.
Cost per m² for EPDM against GRP
MyBuilder's 2026 flat roof guide gives EPDM at £90 to £130 per m² and GRP at £95 to £150 per m². The ranges overlap heavily, and the real difference on a quote is usually smaller than the difference between two roofers or two roof shapes. Complex outlines, many upstands, rooflights and awkward access all add labour to either system.
Repairs follow a similar pattern. Checkatrade's 2026 repair guide puts EPDM repairs at £120 to £170 per m² and GRP at £130 to £180, with VAT and access left out. These are national guide figures and not a price for your roof. After a survey, we write the quote so that it covers the labour and the material.
Laying, movement and repairs
EPDM arrives as a large rubber sheet, and on a simple roof it can sometimes be laid in one piece, which means few seams. It stays flexible, so it moves with the deck as timber expands and contracts. Joints and corners are made with tape and adhesive, and these are the parts that need care. A neat fold at an internal corner or an outlet is a good sign, and baggy or creased corners are worth pointing out to the installer before the job is signed off.
GRP is built up on site, so it forms a continuous, rigid surface fixed to the deck, with no joints across the main area of the roof. That makes it hard-wearing, and it can be walked on. The trade-off is that it is less forgiving of a deck that moves. A rigid skin laid over a flexing or poorly fixed deck can crack, so the deck needs to be sound and well fixed before laying. GRP is also sensitive to weather during laying; see our page on replacing a flat roof in winter.
Repairing each system
A damaged EPDM sheet is repaired with a patch stuck over the damage, or a new section jointed in. GRP is repaired by cutting back to sound material and laying new resin and matting, though matching the old finish and colour exactly can be harder as the surface ages.
Looks, foot traffic and where each suits
EPDM is black as standard, a plain, quiet finish that suits many modern extensions and some period ones. GRP is finished with a coloured topcoat, so it comes in more shades, and the surface can be glossy or textured. Either can be edged with trims in a matching colour. GRP can also be finished to suit stone or render around it, whereas EPDM keeps its dark colour unless it is covered with a walkway or paving tiles. Think about what you will see from upstairs windows, since a flat roof is often the main view for the rooms above an extension.
If the roof will be used as a terrace or walked on regularly, GRP is the more natural choice because of its hard surface. EPDM can take occasional foot traffic for maintenance, but a regularly used roof usually needs a walkway layer or boards over the top.
On a listed or older building, the choice may also be shaped by what the council will accept; our page on flat roofs in Stroud conservation areas covers that.
Choosing between them for your roof
Start with the deck, the falls and the shape of the roof, then weigh the surface you want. A simple rectangle with few penetrations suits EPDM well. A roof with many corners and openings may suit GRP's continuous finish. Sagging or damaged decking comes before either choice and should be put right first. Think too about who will use the roof: a tidy EPDM sheet suits a roof nobody walks on, and a GRP deck suits a roof people step out onto.
If you want a wider comparison that includes felt and single-ply, see our guide to choosing a flat roof material. If you are weighing a new covering against a coating on the existing one, do liquid flat roof coatings work explains where those fit, and putting a new flat roof over the old one covers overlaying.
We will survey your roof with photographs, quote for the whole job and give a 10-year workmanship guarantee in writing. More on both systems is on our flat roofing page.