There is no single best flat roof. EPDM rubber suits simple, square roofs and is quick to lay in one sheet. GRP fibreglass gives a hard, seamless finish that copes well with awkward shapes and light foot traffic. Modern felt (reinforced bitumen) is a proven, layered system that is easy to repair. All three work well if the deck underneath is sound and the roof drains properly. The right choice depends on your roof's shape, how it is used and what is underneath.
How the three systems work
EPDM rubber
EPDM is a synthetic rubber membrane. On most domestic roofs it is laid as a single sheet, bonded to the deck with adhesive, and finished with trims at the edges. Because there are few or no joins on a small roof, there are fewer places for water to get in.
- Flexible, so it copes well as the roof warms and cools
- Fitted cold, with no naked flame on the roof
- Matt black finish that suits garages, extensions and dormers
- Best on simple shapes; lots of pipes, rooflights or corners mean more detailing work
GRP fibreglass
GRP stands for glass-reinforced plastic. Resin and glass matting are laid onto a timber board deck, then a coloured top coat is added. It sets into one hard, seamless layer.
- Very good on awkward shapes, because it is formed on the roof
- Hard-wearing surface that handles occasional foot traffic
- Neat, clean look, with a choice of top coat colours
- Needs dry weather to lay, and a stable deck; if the deck moves, GRP can crack
Felt (reinforced bitumen)
Today's felt is very different from the thin felt many homes still have on their garages. Modern systems use two or three layers of reinforced bitumen membrane, finished with a mineral cap sheet. They are fitted either with a torch or as cold-applied, self-adhesive layers.
- A long-standing system that most roofers know well
- Layered build-up gives a good back-up if the top layer is damaged
- Simple to patch and repair
- Often the most budget-friendly option, though quality varies a lot between systems
What matters more than the material
Most flat roofs fail early for reasons that have nothing to do with the membrane. Before choosing a system, think about:
- The deck. Rotten or soft boards must be replaced. A new membrane laid over a wet, failing deck will not last.
- Falls. A flat roof should never be truly flat. It needs a gentle slope so water runs off. Ponding water is a sign the falls are wrong.
- Edges and upstands. Most leaks start where the roof meets a wall, a gutter or a rooflight, not in the middle of the roof.
- Insulation and condensation. Replacing a flat roof is a good time to add insulation. In many cases the building regulations expect it (see our guide to building regulations when you re-roof). Getting the build-up and ventilation right also helps prevent condensation inside the roof.
- Fire performance. Building control guidance says a new covering should not perform worse in a fire than the one it replaces, so the system has to suit the roof's position, such as close to a boundary.
Which one should you choose?
As a rough guide:
- Single garage or simple rear extension: EPDM is often the neatest, quickest choice.
- Dormer, bay or a roof with lots of corners and pipes: GRP usually gives the cleanest result.
- A roof you want to keep repairable and in keeping with nearby felt roofs: a modern multi-layer felt system works well.
- Roof used as a walkway for access or maintenance: GRP or felt with a hard-wearing finish is usually better than bare EPDM.
What affects the cost and lifespan of any flat roof is the same for all three: the size and shape of the roof, the condition of the deck, how much insulation is needed, access, and the quality of the installation. A well-fitted roof in any of these materials will outlast a poorly fitted one in the "best" material.
If you are planning a new extension or replacing a garage roof, our guide to flat roofs on extensions and garages covers drainage, planning and more.
In Essex, Hertfordshire and Cambridgeshire
Flat roofs are a big part of roofing work across all three counties, largely because of when many homes were built.
- In Basildon, Harlow and Stevenage, a lot of 1950s to 1980s housing has flat-roofed garages, porches, dormers and blocks. Much of the original felt and asphalt now cracks, blisters and ponds water, so flat roof replacement is one of the most common jobs in these towns.
- In Peterborough, the new town townships such as Bretton, Werrington and the Ortons have many 1970s and 1980s homes with their original felt flat roofs and timber fascias.
- On Canvey Island, many bungalows have had dormers and flat-roofed extensions added. The joins between dormers and the main roof, and old cracked felt, are common sources of leaks, and the wind off the estuary adds to the wear.
- In Chelmsford, areas such as Melbourne, Patching Hall, Tile Kiln and Chelmer Village still have many original felt garage roofs that have reached the end of their life.
In all of these places, the right answer usually comes down to the shape of the roof and the state of the deck, which is why we always check the timber underneath first.
How First4Roofcare can help
We fit all three systems, so we can recommend the one that suits your roof rather than the one we happen to sell. See our EPDM rubber flat roofs, GRP fibreglass flat roofs and felt flat roofs pages for more detail. When you are ready, book a free roof survey and we will check the deck, the falls and the edges, explain your options and give you a free written quote.