The short answer
There is no single best flat roof material for every home. EPDM rubber is a single flexible sheet that suits most domestic roofs and has few seams. GRP fibreglass is laid wet and cures into a hard, seamless surface that suits roofs with foot traffic or lots of detailing. Built-up felt is a traditional layered system that remains a practical choice on many roofs. The right answer depends on the roof’s size, shape, use and budget.
EPDM rubber roofing
EPDM is a synthetic rubber membrane, usually laid as one large sheet bonded to the deck. On a typical extension or garage it can often cover the whole area without joins, which removes the seams where many flat roof leaks begin.
The rubber stays flexible through hot and cold weather, allowing it to cope with the small movements every roof makes. Edges are finished with trims and the membrane is dressed up walls to form upstands. It is laid cold, so no naked flame is needed on the roof.
Its appearance is a plain dark grey or black surface. Complicated roofs with many penetrations need careful detailing, and the membrane can be damaged by sharp objects, so it is best where there is little foot traffic.
GRP fibreglass roofing
GRP is glass-reinforced polyester. Resin and a glass fibre mat are laid over a board deck on site, then a coloured topcoat is applied. Once cured, it forms a rigid, seamless shell.
The hard finish suits roofs that will be walked on for maintenance and roofs with lots of shapes, because the material can be formed around details. It depends on dry weather and correct temperatures while it cures, and rigid surfaces need proper movement allowances on larger roofs.
Felt roofing
Modern felt roofs are built from several layers of reinforced bitumen membrane, usually torched or bonded together, often with a mineral cap sheet on top. They are a long-established system that many roofers know well.
Felt has more joins than a single EPDM sheet, and older felt roofs are the ones most often seen with blisters, cracking and splits. A modern, well-installed built-up system is a different product from the single-layer felt found on many old garages.
Side-by-side comparison
The key differences are usually these:
- Seams: EPDM can often be one sheet; GRP is seamless once cured; felt has overlapping layers.
- Installation: EPDM is bonded cold; GRP is laid and cured on site; felt is commonly torched on.
- Weather sensitivity: GRP and bonded systems need dry conditions; all systems need a dry deck.
- Foot traffic: GRP copes best; felt with a mineral cap is reasonable; EPDM prefers little traffic.
- Detailing: GRP forms around complex shapes easily; EPDM and felt rely on trims and accessories.
- Appearance: EPDM is plain dark grey; GRP can be coloured; felt often has a mineral finish.
Which one suits your roof?
For a straightforward garage or single-storey extension with little foot traffic, EPDM is often a sensible, tidy choice. Where the roof has many corners, rooflights or is used for access, GRP may be worth considering. Felt can still make sense where a layered bitumen system matches the building or budget.
Condition matters more than material. Any of these coverings will fail early on a rotten deck, poor falls or badly finished edges, so the preparation should be discussed as carefully as the covering.
Our flat roofing work
Rayner’s Roofing installs and replaces flat roofs for homeowners, and our recent projects include rubber EPDM roofs on extensions. We can look at your roof and explain which option suits it before providing a quotation.
Frequently asked questions
Is EPDM the same as a rubber roof?
Yes. EPDM is the synthetic rubber membrane most people mean when they talk about a rubber flat roof.
Can you walk on a rubber roof?
Occasional careful access for maintenance is normal, but regular foot traffic is better suited to GRP or a protected surface.
Can a new flat roof go over the old one?
Overlaying is sometimes possible, but stripping back lets the deck be checked. Hidden rot under an old covering is a common cause of new roofs failing early.
Which flat roof is quietest in rain?
Noise depends more on the deck and insulation beneath than on the membrane. An insulated warm roof is usually quieter than an uninsulated one.