EPDM vs GRP vs Torch-On Felt: The Flat-Roof Comparison

Three systems cover almost every domestic flat roof: single-ply EPDM rubber, GRP fibreglass, and torch-on felt. The right pick depends on the deck, the detailing and how long the roof is expected to last.

EPDM rubber is a large sheet vulcanised on site with heat-welded or taped seams. Well-installed EPDM commonly performs for 25+ years, handles building movement, and detail work is straightforward.

GRP (glass-reinforced plastic) is laid up wet as a seamless membrane. Excellent walk-on strength and rooflight kerb detailing, but sensitive to deck movement and cold-day installation — GRP that cracks tends to crack repeatedly.

Torch-on felt is the traditional multi-layer bituminous system. Cost-effective and reliable when correctly installed; expect 15–20 years depending on grade. Watch for weld failure at laps as it ages.

For a new extension roof we usually recommend EPDM or GRP — the small extra cost buys another 5–10 years and better detail work. For a straight replacement over a sound deck, budget can steer the choice.

Whichever system, the failure point is almost always the detail: upstands, drips, penetrations and rooflight kerbs. Ask any quoting roofer to explain those details before you sign.