Service
Flat Roof Cost: GRP vs EPDM vs Felt
Homeowners ring asking the price of EPDM when the membrane is often the smallest part of the bill. The deck, the falls, the insulation and the trims decide most of it. Once those are settled, the choice between GRP, EPDM and felt is about lifespan and whether you will walk on it.
- Relative cost order of the three systems
- Why the deck usually decides the price
- Building regulations and insulation upgrades
- Which system suits a garage, extension or balcony
- We fit all three, so no bias
- Free quote, guaranteed workmanship
Cost order, cheapest first
Per square metre, torch on felt is the lowest, EPDM sits in the middle and GRP fibreglass is the highest of the three. Lifespan runs the other way, with felt at roughly ten to twenty years and both EPDM and GRP at twenty to thirty. Over the life of the roof, felt is rarely the cheap option it looks on the day.
The deck is the real variable
If the boards under your old covering are wet, soft or springy, they come off. New deck, new firrings to correct the falls and new trims can outweigh the membrane cost entirely. This is exactly why an honest quote is written after someone has been up and probed the deck, not after a phone call.
Insulation and building regulations
Replacing the whole covering over a heated room usually triggers a requirement to bring insulation up to current standards. That means either a warm roof build up above the deck or insulation between and under the joists, and it is a real cost that a suspiciously cheap quote may have quietly ignored. We say so at quote stage rather than after.
Picking by use, not by price
Garage or shed: EPDM, one sheet, no field seams, simple to repair years later. Balcony, terrace or anything you walk on: GRP with a non slip topcoat. Tight budget on a structure with limited life left: felt is a legitimate choice and we will fit it properly rather than talking you up.
FAQs
Can a new membrane go over the old one?+
We do not recommend it. Overlaying traps a wet deck and voids most manufacturer guarantees, so we strip back and inspect.
Which is cheapest to repair later?+
EPDM. A patch is quick and blends into the sheet. GRP repairs need dry weather to cure and felt repairs tend to lead to more felt repairs.
How long does a garage roof take?+
A single garage is normally one day. An extension roof needing a new deck and trims is two to three.
Do you quote the deck separately?+
Yes. Deck, insulation, membrane and trims are itemised so you can see exactly where the money goes.
Related reading
Other pages homeowners usually look at alongside this one.
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