Felt vs EPDM vs GRP: choosing a flat roof system
There is no single best flat roof system — there is a best system for a particular deck, shape and use. Here is how the three common options actually differ.
Torch-on felt
Cheapest to install, widely understood, and repairable by anyone. Its weakness is seams: every lap is a future failure point, and typical life is shorter than the alternatives.
EPDM rubber
One continuous sheet on most domestic roofs, so no field seams. Very good lifespan for the money, quick to install, and forgiving of deck movement. Weakest on heavily trafficked roofs.
GRP fibreglass
A rigid, seamless, walked-on finish that suits balconies and terraces. More weather-dependent to install, more expensive, and it can crack where the deck flexes or where thermal movement is significant.
Choosing by use
Garage or extension nobody walks on: EPDM. Balcony or roof terrace: GRP or an equivalent hard system. Tight budget on a short-term property: felt, understood as a shorter-life choice.
The detail matters more than the material
Most flat roofs we're called to didn't fail in the middle of the field. They failed at an upstand, a trim, an outlet or an abutment. Whichever system you choose, the detailing is what buys the years.
FAQs
For a typical domestic extension or garage that isn't walked on, EPDM usually gives the best cost per year of service.
Occasional maintenance access is fine. Regular foot traffic needs walkway protection or a different system.
No. On decks that move, rigidity is a disadvantage — that's exactly where hairline cracking appears.
Related reading
More on comparisons and the jobs that usually come with it.
- Slate vs tile: which suits your propertyComparisons
- Flat roof systems compared and how long each lastsComparisons
- Roofer or general builder: who should do the workComparisons
- Scaffolding for roof work: when you need it and what it costsCosts & budgeting
Looking for something specific? See our roofing services, cost guides, common roof problems or the areas we cover.
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