The quick comparison
- EPDM rubber: Best all-rounder for most domestic flat roofs. Long-lasting, flexible, single-piece on most installs. £80–£120/m² installed.
- GRP fibreglass: Best when the roof needs to be walked on (terraces, balconies). Tough, seamless. £100–£140/m² installed.
- Modern felt: Best for budget-conscious projects on simple flat roofs. £60–£90/m² installed. Shorter lifespan.
Now let's go properly through each option.
EPDM rubber — the all-rounder
What it is
EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane, usually 1.2–1.5mm thick. For most domestic roofs, the entire roof is covered by a single sheet of rubber, glued to the deck. No joins on a typical garage roof.
Pros
- 30–50 year lifespan — by far the longest of the three
- Very few joins — single-piece installation on most domestic roofs eliminates the most common failure point
- Highly flexible — moves with the building, doesn't crack from temperature changes
- UV-resistant — degrades far slower than felt
- Low maintenance — practically zero once installed
- 20-year manufacturer warranty standard
Cons
- Not designed to be walked on regularly — punctures from sharp objects can occur
- Glue-bonded — quality of installation matters
- Doesn't look as smart as fibreglass for visible roofs
Best for
Garage roofs, single-storey extension roofs, dormer roofs, porch roofs — any flat roof that you don't need to walk on. This is what we recommend most often for Worcestershire properties.
GRP Fibreglass — the tough option
What it is
GRP (Glass Reinforced Polyester) is liquid resin and glass mat laid in-situ. It cures into a single rigid waterproof shell — like a fibreglass boat hull on your roof.
Pros
- 30+ year lifespan
- Walkable — strong enough for terraces, balconies, regular foot traffic
- Seamless — no joins anywhere
- Can be coloured — multiple finish options for visible roofs
- 25-year warranty typical
- Very weather-tough — handles heavy rain, hail, frost
Cons
- More expensive than EPDM
- Less flexible — can crack on substrates that move significantly
- Weather-dependent install — needs dry conditions to cure properly
- Repairs are visible — patching shows more than EPDM
Best for
Roof terraces, balconies, walkways, dormers visible from the ground. Also good for unusual shapes and tight detailing — GRP can be moulded to almost any form.
Modern felt — budget-friendly
What it is
Today's felt is far better than the 1980s stuff. Modern systems use modified bitumen with polymer additives, applied in 2–3 layers, torched into place. Sometimes called "high-performance felt" or "3-layer torch-on".
Pros
- Cheapest of the three
- Quick to install
- Tried and tested — has been used for decades
- 15–25 year lifespan with modern systems
Cons
- Shorter lifespan than EPDM or GRP
- Multiple seams — every join is a potential failure point
- Becomes brittle with age — flexibility decreases over time
- Requires hot torch installation — small fire risk during fitting
- UV degrades it faster than alternatives
Best for
Budget-constrained projects on simple, hidden flat roofs. Garage roofs where the owner doesn't plan to be in the house long-term. We don't recommend felt for new installations on visible or main-property roofs — the long-term cost works out higher because you'll be replacing it twice as often as EPDM.
Cost comparison for typical Worcestershire jobs
Single garage flat roof (about 20 m²)
- Felt: £1,500 – £2,400
- EPDM: £1,800 – £2,800
- GRP: £2,200 – £3,500
Kitchen extension flat roof (about 30 m²)
- Felt: £2,200 – £3,500
- EPDM: £2,500 – £4,500
- GRP: £3,000 – £5,500
Roof terrace / balcony (about 15 m²)
- Felt: Not recommended (not walkable)
- EPDM: Not ideal (not designed for foot traffic)
- GRP: £2,500 – £4,500 — clear winner
Lifetime cost comparison
Over 50 years on a £2,500 garage roof:
- Felt: Replace every 20 years = 2.5 replacements = £6,250 total
- EPDM: Replace every 40 years = 1.25 replacements = £3,500 total (best value)
- GRP: Replace every 35 years = 1.4 replacements = £4,200 total
EPDM wins on lifetime cost for any roof lasting longer than 15 years.
What we recommend in Worcestershire
After a decade of installing all three across the county:
- Domestic garage / single-storey extension → EPDM, every time
- Terrace, balcony, walkable area → GRP
- Dormer, complex shape, visible from the ground → GRP for the looks
- Tight budget on a hidden flat roof you'll see in 20 years → modern felt
- Listed building or conservation area → check material requirements first
Get the right system for your property
We install all three systems and we'll advise honestly on which makes sense for your specific roof. The free survey takes 30 minutes; the written quote arrives within 24 hours.
Call 07930 965629 or email us. ASH Roofing covers all of Worcestershire.