Built-up felt
- Layers of modern reinforced bitumen membrane, bonded together. Often called torch-on felt when heat-applied.
- A long-established system that many roofers install.
- Ask whether the roofer uses heat (a torch) and how they manage fire risk; cold-applied and self-adhesive systems also exist.
EPDM (rubber)
- A single sheet of synthetic rubber membrane, bonded to the deck.
- Often laid in one piece on smaller roofs, so there are few or no joins.
- Usually installed cold, with adhesive, so no flame is needed.
GRP (fibreglass)
- Glass-reinforced plastic laid as a liquid resin with glass matting, which cures to a hard, seamless surface.
- Can be shaped around details and finished in different colours.
- Needs dry conditions and suitable temperatures to cure properly, so timing matters.
Whatever the covering
- The deck matters: a covering is only as good as the boards beneath it. Ask whether the deck will be replaced.
- Falls: a flat roof still needs a slight slope so water drains off rather than pooling.
- Insulation and condensation: warm-roof construction, with insulation above the deck, is common in new and replacement flat roofs. Ask your roofer how they will avoid condensation.
- Guarantee: ask what the manufacturer and the installer each guarantee, and for how long.
Next steps
Replacing a large flat roof may need Building Regulations approval. Get itemised quotes from local roofers for the same specification so you can compare like for like.
Last updated: 14 October 2026
