Flat Roofing: GRP, EPDM & Felt

Flat roofs get a bad name because so many were built badly: no falls, poor detailing at the edges, and felt that was never meant to last twenty years. A modern flat roof, properly designed and installed in GRP, EPDM or a good three-layer felt, is a reliable, long-lived roof with a manufacturer-backed guarantee.

We install all three systems and will tell you which suits your roof rather than pushing the one we prefer. The answer depends on the size and shape of the roof, whether anyone will walk on it, the budget, and what is underneath.

Before and after: felt flat roof with new rooflight

A tired, patched felt roof over a rear extension, replaced with a new torch-on felt system and a fixed flat glass rooflight in place of the old polycarbonate dome. Edge trims, upstands and the flue were all re-detailed.

Old patched felt flat roof with a domed rooflight before replacement — Before

New torch-on felt flat roof with a flat glass rooflight after replacement — After

Worn felt flat roof surface before replacement, looking along the extension — Before

Finished felt flat roof looking along the extension after replacement — After

Warning signs

Standing water after rainPonding means inadequate falls; it shortens the life of any system.

Blisters or bubblesTrapped moisture in felt. Patchable short-term, a replacement signal long-term.

Cracks at laps or upstandsThe edges fail first on felt roofs.

Sagging deckRotten boards beneath the covering; the deck needs replacing, not just the membrane.

Moss and vegetationHolding water and blocking outlets.

Damp on the ceiling belowOften shows some distance from the actual leak as water tracks along the deck.

What we do

GRP fibreglass flat roofs, seamless and walkable
EPDM rubber single-sheet roofs
Three-layer torch-on felt systems
Replacement decking in 18 mm WBP or OSB3 with built-in falls
Warm-roof insulation build-ups to current regulations
Outlets, drips, upstands and trims detailed properly
Patch repairs where the roof has life left in it
Flat-to-pitched conversions where a flat roof keeps failing

Materials and methods

GRP: Cure It or Cromar resin systems with 450 g mat and a 20 or 25-year guarantee. EPDM: Firestone RubberCover or ClassicBond with a 20-year guarantee. Felt: SBS-modified three-layer systems with a 15-year guarantee. Insulation: PIR boards to Part L. Full comparison in our flat roof guide.

Why choose us for flat roofing

Honest advice on which system suits your roof
Falls designed in, so water drains rather than ponds
Long manufacturer guarantees registered in your name
Workmanship guarantee on top
Most domestic flat roofs completed in one to three days

What to expect

We inspect the surface and, where possible, check the deck from below. If the deck is sound we quote for a new covering; if not, we quote for deck replacement too. GRP is laid only in dry weather on a dry deck; we schedule for the forecast rather than rush it.

Related projects

Flat roof

Felt flat roof and rooflight replacement

Old felt stripped, new torch-on system laid and a flat glass rooflight fitted.

All projects →

Frequently asked questions

Which flat roof system lasts longest?

EPDM and GRP both outlast felt by a wide margin. EPDM has a slight edge on large simple roofs; GRP wins where there are details or foot traffic.

Can you fit a flat roof over the existing one?

Sometimes, if the deck is sound and dry. Often it is better to strip, check the deck and start clean, particularly if there has been a leak.

Can I turn my flat roof into a terrace?

With a GRP system on a suitably strong deck, yes, including non-slip finishes and upstands.

Why does my flat roof leak when the hole is not where the damp is?

Water travels along the deck and insulation before it finds a way through. We trace the actual entry point rather than patching the wet spot.