A leaking garage, a kitchen extension or a tired dormer roof usually leads to the same comparison: EPDM rubber, GRP fibreglass, or felt. Each has a place. The mistake is to choose a name first and look at the deck afterwards.
Summit Roofing specifies flat roofs in EPDM, GRP and felt from the building outwards: the deck, the falls, the outlets, the upstands and how the roof is used. This article is a plain guide to those choices, not a ranking of brands.
Start with the deck and the water
A “flat” roof still needs a fall to an outlet or a drip. If the deck has sagged, or an internal outlet is poorly placed, water will stand. Standing water is one of the most common reasons a covering ages early. No membrane — rubber, fibreglass or felt — enjoys sitting in a permanent puddle.
So the first questions are practical. Is the deck sound? Is there insulation that has to be kept or improved? Where does the water go? How does the roof meet the house wall, a rooflight kerb or a parapet? Those junctions leak more often than the middle of a tidy bay.
EPDM rubber
EPDM is a flexible rubber membrane, usually laid in large sheets with bonded laps and dressed upstands. It suits many domestic extension and garage decks, and it copes well with a little movement if the substrate is properly prepared. Details still matter: trims, outlets, corners and the way the membrane turns up a wall are where most problems start.
Typical UK guide rates for EPDM often sit around £70 to £130 per square metre, depending on insulation, deck repairs and the complexity of the edges. That is a guide, not a quote; see the costs page.
GRP fibreglass
GRP is a built-up, hard, joint-light finish, usually with a coloured top coat and a trim system around the edge. It can be an excellent covering on a regular, well-prepared shape. It is less forgiving if the weather turns during install, or if the roof is a complicated collection of steps and pipes. As with EPDM, the kerbs around roof windows and the abutment to a pitched roof above have to be designed, not improvised.
Guide rates in the UK are often quoted around £80 to £150 per square metre. Again, the edges and the deck will move that more than the brochure will.
Felt
Modern built-up or single-ply felt systems still have a place, especially on simpler outbuilding roofs. Older mineral felt that is already cracked, blistered or overlaid more than once is a different story. Patching a split bay can be a sensible holding repair; another overlay on a tired, wet deck is often just hiding the next leak. Typical UK guide rates for felt are often a little lower per square metre, commonly £50 to £90, which is one reason people ask for it — and one reason the specification has to stay honest about what you are buying.
Repair or replace
A local puncture or a failed trim on an otherwise recent, sound covering can often be repaired. A felt roof that is cracked across the bays, or a covering that has already been layered up, is usually a replacement job. We would rather say which it is than sell a short overlay that traps problems underneath.
If you are deciding, send photographs of the deck, the edges and any rooflights, plus your postcode, via the quote form. A survey will talk about drainage as much as about the membrane. The process from there is a written scope, not a product name on its own.
