REF · MATERIAL GUIDE · FLAT ROOFS
EPDM vs felt flat roof — the honest comparison
Two materials, very different economics. Sean Brown explains what we fit, what we don’t, and why the £-per-year-of-life metric matters more than the upfront cost.
The 30-second answer
What is felt? (and why we don’t fit it any more)
Felt — properly “built-up roofing felt” — is a bituminous mineral-coated sheet, laid in 2 or 3 layers with hot bitumen or self-adhesive layers between. It’s been the default UK flat-roof material since the 1960s.
The problem: felt is sacrificial. UV degrades it. Frost cracks it. Thermal movement opens the seams. A felt flat roof needs replacing every 8–12 years on average — sometimes sooner if it’s south-facing or sees standing water.
When we’d still use felt
One scenario only: a tenant won’t be there long enough to benefit from EPDM and the landlord wants the cheapest patch. We’ll do it, we’ll quote it, but we’ll always tell you what the EPDM upgrade costs first.
What is EPDM?
EPDM is ethylene propylene diene monomer — a synthetic rubber single-ply membrane. Fitted as a single sheet (or welded multi-panel) to a primed deck. We use Firestone Elevate™ EPDM — branded, warranted, manufacturer-named on every quote.
Why EPDM wins
- One sheet, no seams on most domestic jobs — no joints to fail
- 20-year material warranty from Firestone (pass-through, in your name)
- UV-stable — doesn’t degrade in sunlight
- Stays flexible at −40 °C — no cold cracking
- Walkable for maintenance access without damage
- Recyclable at end-of-life (felt goes to landfill)
The £-per-year-of-life numbers
| Property | Felt fitted | EPDM fitted | Lifespan diff |
|---|---|---|---|
| Garage (12 m²) | £600–£1,200 | £720–£1,560 | ~9× longer |
| Single-storey extension (20 m²) | £900–£2,000 | £1,200–£2,600 | ~9× longer |
| Large extension (30 m²) | £1,400–£3,000 | £1,800–£3,900 | ~9× longer |
The headline price gap is 20–30%. The lifetime cost gap is the other way round: EPDM is roughly half the per-year-of-life cost.
What about GRP, single-ply PVC, asphalt?
Three quick mentions:
- GRP (fibreglass) — wet-look black, 25-year life, £45–£80/m² fitted. We fit on dormers and small flat roofs but not large spans (it’s brittle in extreme cold). See our GRP dormer service.
- Single-ply PVC — commercial-grade. Excellent material but overkill for domestic.
- Mastic asphalt — traditional, 50-year life, but requires hot working and £80+/m². We don’t generally fit on domestic; it’s overspec.
If your current flat roof is felt
The honest assessment:
- Under 8 years old, no leaks, no bubbles — leave it. We’ll come back in 4–6 years for a re-survey.
- Bubbles, lifting, ponded water — it’s near end of life. EPDM replacement now beats waiting for a leak.
- Active leak — emergency tarp, then EPDM replacement on the next dry day.
Common questions
Can EPDM be fitted in winter?
Yes — EPDM stays flexible to −40 °C. We’ve fitted in January. The only blocker is rain (we don’t lay membrane on a wet deck).
Is EPDM the same as ‘rubber roofing’?
EPDM is the most common type of rubber roofing in UK domestic. Other rubber-family membranes exist (TPO, butyl) but EPDM is the proven default.
What’s the warranty?
Firestone EPDM: 20-year material warranty in your name. Our labour: 10-year guarantee in writing.
Can I walk on an EPDM roof?
Yes — for occasional maintenance access (cleaning a Velux, checking the chimney). Not for daily foot traffic — that needs a walkway pad or paving slabs.
