EPDM vs GRP vs Single Ply: Which Flat Roof Is Best?
If you’re replacing a flat roof in Doncaster, three systems come up again and again: EPDM rubber, GRP fibreglass and single ply membrane. They’ll all keep the rain out on day one, but they don’t age the same way, and over twenty years the differences are stark. We fit flat roofs across South Yorkshire every week, and single ply is the system we recommend almost every time. Here’s an honest explanation of why.
The problem with GRP fibreglass
GRP (glass reinforced plastic, or fibreglass) is laid wet, as layers of resin and matting that cure into one hard, solid surface. It looks smart when it’s new, which is why it gets specified on balconies and walk-on areas.
The trouble is what happens afterwards. GRP is rigid, and a flat roof is not a static thing: the deck below expands, contracts and flexes with temperature and load. A brittle surface bonded to a moving deck is a recipe for stress cracks and gel-coat crazing, and once GRP cracks, water gets straight into the structure.
It’s also one of the most weather-dependent and installer-dependent systems there is. GRP needs dry, reasonably warm conditions to cure correctly. Rush it, catch a shower mid-cure or get the resin ratios wrong and you’re left with a roof that never reaches full strength. The finish is only ever as good as the day it was laid.
The problem with EPDM rubber
EPDM is a synthetic rubber sheet, usually glued down and joined at the seams and details with adhesives and tapes. On a small, simple square roof a good EPDM job can last a while, and that’s the strongest thing we’ll say for it.
The weakness is built into how it goes together. Every lap, corner, upstand and outlet relies on an adhesive bond, and adhesive is the part that ages: UV, heat cycling and time all work against it. When a rubber roof leaks, it’s almost always at a glued joint or a bonded detail, not in the middle of the sheet. The bigger or more complicated the roof, the more glued joints there are, and the more there is to fail.
Why single ply membrane is the better product
Single ply is a high-performance PVC or TPO membrane laid over insulation, and here’s the part that changes everything: the seams are hot-air welded, fusing the sheets into one continuous, homogeneous skin. A properly welded seam is actually stronger than the membrane around it.
That single difference removes the weak point that undoes both GRP and EPDM:
- No glued laps to perish like EPDM, and no rigid shell to crack like GRP.
- It stays flexible, so it moves with the building instead of fighting it.
- It welds in cool, variable weather, so installation isn’t hostage to a dry forecast.
- It carries a genuine manufacturer guarantee of 20 to 25 years and upwards, backed by approved installation.
It’s the system used on the vast majority of modern commercial buildings, for exactly these reasons, and it works just as well on a house, an extension or a garage.
Head to head
- Seams: Welded single ply (strongest) beats glued EPDM and beats rigid, crack-prone GRP.
- Movement: Single ply flexes; GRP cracks; EPDM copes but leans on adhesive.
- Weather to install: Single ply and EPDM are forgiving; GRP needs dry, warm curing.
- Lifespan: A quality single ply membrane carries a 20 to 25 year guarantee and often outlasts it.
- Where each suits: Single ply for almost everything; GRP only where a hard walk-on finish is essential; EPDM only on the smallest, simplest roofs.
Single ply flat roofing in Doncaster and South Yorkshire
We’re based in Armthorpe and install single ply flat roofing on homes and businesses right across the region, from Doncaster town centre to Rotherham, Barnsley, Mexborough and the villages in between. Whether it’s a leaking garage in Bessacarr, an extension in Bawtry or a commercial unit near the M18, we specify the membrane that fits the roof and weld it into a roof that lasts. You can see every area we cover on our areas page.
If you’re weighing up a full re-roof, our guide to single ply vs felt is worth a read too.
Want a straight recommendation for your roof? Get a free quote or call us on 07973 436 305.
Frequently asked questions
Is single ply better than EPDM rubber?
In most cases, yes. EPDM relies on adhesives and tapes at its seams and detailing, and that bond is where rubber roofs tend to fail first as they age. Single ply seams are hot-air welded into one continuous skin, with no glue to perish or peel, so there is far less to go wrong over the life of the roof.
Is single ply better than GRP fibreglass?
For most roofs, yes. GRP is rigid, so it can craze and crack where the deck moves or with normal thermal expansion, and it needs dry, settled weather to cure properly. Single ply stays flexible, absorbs that movement and can be welded in cooler, more variable conditions, which is why we fit it across South Yorkshire all year round.
Does single ply cost more than EPDM or GRP?
The up-front difference is usually small, and it depends far more on the size, detailing and access of your roof than on the membrane. Spread over a 20 to 25 year manufacturer guarantee, single ply normally works out better value than re-doing a shorter-life covering.
Do you install single ply flat roofing in Doncaster?
Yes. We are based in Armthorpe and fit single ply flat roofs across Doncaster, Rotherham, Barnsley, Mexborough and the surrounding South Yorkshire towns. You can see the full list on our areas we cover page.
How long does a single ply flat roof last?
A correctly installed single ply roof typically lasts 25 to 35 years, and many membranes carry a manufacturer guarantee of 20 years or more. Felt, by comparison, often needs replacing in 10 to 15 years.