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Flat Roof Systems Compared: EPDM, GRP, Felt and Single Ply
For a straightforward garage or extension roof, EPDM is usually the best value. For a balcony or anything you walk on, GRP. Felt is the cheapest up front and the shortest lived. Single ply suits larger commercial decks. The deck underneath matters more than the material on top.
- Four systems, honest side by side
- Typical lifespan and cost order
- Which ones you can walk on
- Where each one actually fails
- We fit EPDM, GRP and felt, so no bias
- Free quotes, guaranteed workmanship
The four systems at a glance
Take these as working expectations for a domestic roof correctly installed on a sound deck.
- ▸EPDM rubber: 20 to 30 years, single sheet with no field seams on most domestic roofs, flexible in cold, cheap to repair
- ▸GRP fibreglass: 20 to 30 years, rigid seamless shell including trims, takes a non slip walk on finish, needs dry weather to cure
- ▸Torch on felt: 10 to 20 years, lowest up front cost, multiple laps that eventually blister or split
- ▸Single ply (PVC or TPO): 25 years plus, hot air welded seams, best suited to larger commercial roofs
Which one can you walk on
GRP with a non slip topcoat is the proper choice for a terrace or balcony. EPDM takes occasional maintenance access but is not a walking surface unless a walkway layer is added. Felt scuffs and single ply is fine for maintenance traffic but not as a finished floor.
Where flat roofs really fail
Almost never in the middle. They fail at the perimeter, at upstands, around soil pipes and rooflights, and wherever water sits because the falls are wrong. A wet or springy deck under a new covering will bring any of these systems down early, which is why we strip back, check the boards and correct the falls with firrings before anything is bonded down.
Cost order and what changes it
Cheapest to dearest per square metre is generally felt, then EPDM, then GRP, then single ply, but the covering is only part of the bill. Deck replacement, insulation upgrades to meet current building regulations, new trims and access or scaffold can move a quote more than the choice of membrane does. We price the deck and the detailing openly rather than hiding them in a rate.
FAQs
Can a new covering go over the old one?+
We do not recommend it. Overlaying traps a wet deck and voids most manufacturer guarantees. We strip back and inspect.
Which is best for a garage roof?+
EPDM in most cases: one sheet, no seams, quick to fit and simple to repair years later.
Do I need insulation upgrading?+
If you are replacing the whole covering on a heated space, building regulations usually require the insulation to be brought up to standard. We will tell you at quote stage.
How long does the work take?+
A typical single garage roof is one day. An extension roof with deck replacement and new trims is usually two to three.
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