Flat roofing specialists — Merseyside & North West

Flat roofs have a bad reputation, mostly because a generation of cheap mineral felt installations from the 1970s and 1980s all failed at once. Modern flat roofing is a completely different animal: properly specified, properly installed, and properly guaranteed, a flat roof should last 25 to 50 years with no maintenance beyond occasional gutter clearing. Liverpool Roofs fits the three most common domestic flat roof systems — EPDM rubber, GRP fibreglass, and torch-on felt — plus commercial single-ply (Sika, IKO Armourplan) for larger jobs.

EPDM rubber (Firestone RubberCover & Classicbond)

Our most popular domestic flat roof. EPDM is a single-piece rubber membrane — one sheet covers the whole roof with no seams on typical domestic extensions. It handles UK temperature swings brilliantly (tested from −40°C to +120°C), doesn't go brittle like felt, and carries a 20-year manufacturer warranty as standard. Installation is fully bonded with water-based adhesive, no torches, no open flames, so it's safe to fit adjacent to timber and on converted outbuildings.

Typical price for a single-piece Firestone EPDM on a 25m² kitchen extension: £2,800–£3,800 including strip, 18mm OSB deck, rubber, trims, and gutter outlet. Expected life: 25–50 years.

GRP fibreglass

GRP (glass-reinforced polyester) gives you a hard-wearing, seamless finish that's ideal for balconies, roof terraces, and dormer roofs where someone might walk on it. It's cold-applied as a liquid and cures to a solid glassy finish — no joints, no seams, and it can be formed around awkward shapes, drains and pipe penetrations that would be fiddly in sheet materials. We use IKO Topseal and Cromar ProGRP systems. 25-year warranty, 30-year expected life.

Downside: GRP can crack if the deck flexes (so it's only suitable over a rigid, properly-spec'd plywood or OSB base), and it's more expensive than EPDM. Typical 25m² install: £3,200–£4,400.

Torch-on felt (SBS modified bitumen)

The modern replacement for old 1970s mineral felt. A three-layer SBS-modified torch-on system (vent layer, underlayer, mineral cap sheet) from IKO, Chesterfelt, or Langley. Fitted with a gas torch — which means it shouldn't be the first choice for extensions next to timber sheds or fences, but where access is good it's a robust, cost-effective option with a 20–25 year life. Typical 25m² install: £2,400–£3,200.

Commercial single-ply (Sika Sarnafil, IKO Armourplan)

For industrial and commercial flat roofs above 100m² we move up to mechanically-fixed PVC or TPO single-ply. We're accredited installers for Sika Sarnafil and IKO Armourplan, which means their warranty paperwork carries full manufacturer backing (typically 15–25 years depending on spec). Used on warehouse roofs, retail units, schools, and care homes across the North West.

Signs your flat roof needs replacing

• Ponding water — water that sits on the roof for more than 24 hours after rain has stopped. Usually caused by deck sag or insufficient falls.
• Blistering, cracking or crazing — old felt develops blisters as trapped moisture expands in heat. The felt cap sheet crazes, then the waterproofing fails.
• Moss and organic growth — a sign the surface is staying wet for long periods.
• Sagging between joists — often means the deck underneath has rotted. Stand under the roof in the room below and check the ceiling for dips.
• Damp patches on the ceiling below — the obvious one. But worth knowing that a flat roof leak can migrate along the deck for several metres before showing, so the drip inside rarely matches the hole outside.
• Age over 25 years for felt, 20 for GRP without maintenance — most materials have done their time by then.

Full strip vs overlay

The short answer: we almost always strip. Overlaying a new membrane over an old one hides problems (rotten deck, trapped moisture, failed insulation) and voids most manufacturer warranties. The only time we'd recommend an overlay is on a very recently installed system with a known failure point — which is rare.

A proper flat roof replacement means: strip to the deck, inspect the joists, replace rotten deck in 18mm OSB3 or WBP ply, fit 100mm PIR insulation if it's a warm roof, fit new membrane with proper falls (minimum 1:80), new trims, new outlets. Job done right, warranty registered, paperwork sent across.