Last reviewed: 2026
There is no single best flat roof system for every situation. Felt, GRP and EPDM can each perform well when properly specified. The deck's condition and tolerance of movement, the roof's shape and penetrations, drainage falls, expected foot traffic and the installer's experience with the chosen system should decide between them, more than any one material's general reputation.
Why the question has no single answer
Flat roof coverings are frequently compared as if one material is simply superior to the others, but the systems suit different circumstances. A small domestic extension roof, a large commercial deck and a heavily trafficked balcony all place different demands on a covering, and the right choice reflects those demands rather than a general preference.
What the roof sits on matters as much as what sits on top of it. A timber deck that flexes with temperature and moisture calls for a covering that can accommodate movement; a stable, well-braced deck opens up more options. Where the existing deck is uncertain, that uncertainty should be resolved before a system is chosen rather than covered over and hoped for the best.
Torch-on felt
Multi-layer torch-applied systems are the traditional choice and remain a good one. They are economical, straightforward to repair locally, and tolerant of imperfect decks. Expect a shorter design life than GRP or EPDM, and expect the detailing at upstands and outlets to be what determines how it performs.
GRP fibreglass
GRP is laid wet and cures into one seamless rigid layer with no joints to fail. It suits roofs with rooflights, upstands, kerbs and awkward junctions, and it takes foot traffic well. It needs a sound, dry, correctly boarded deck and dry weather to install, so it is more weather-dependent than the alternatives.
EPDM rubber
EPDM is a single sheet of synthetic rubber, usually installed in one piece on domestic-sized roofs. It stays flexible in cold weather, accommodates deck movement and installs without heat. Its performance depends on the bond and on well-formed corners and trims, and on the adhesive or ballast method chosen for the substrate it is being fixed to.
What we would check
Falls, drainage capacity, the number and type of penetrations, whether the roof will be walked on, and how the edges and abutments are detailed all shape which system is appropriate. A system chosen without reference to these factors can underperform however good the material's general reputation.
- Deck material, condition and any signs of deflection or decay
- Existing falls and where water currently drains to
- Number, type and condition of penetrations and upstands
- Whether the roof is or will be subject to foot traffic
- Any history of leaks or previous repairs on the existing covering
Repair, replace or monitor
Where the deck and falls are sound, a failing covering can often be re-covered without wider work. Where the deck has deteriorated or falls are inadequate, addressing those issues alongside a new covering is usually more durable than covering over them. A covering nearing the end of its service life but still watertight can be reviewed periodically rather than replaced immediately, with the review focused on the same details that decided the original specification: falls, penetrations and edge trims. Whichever system is chosen, insulation, falls to the outlet and upstand heights matter more than the brand on the datasheet, and an installer unfamiliar with the specific system is a greater risk than the material itself.