Flat Roofs
Flat Roof Replacement Cost: What You’re Really Paying For
We quote flat roof replacement in GRP fibreglass (our recommended system, £2,500–£4,500 for a standard garage or extension) or EPDM rubber (£2,800–£5,000). We don't install new felt roofs — if your existing roof is felt, replacing it with GRP or EPDM is a genuine upgrade, not just a like-for-like swap.
Flat roofs are one of the most common jobs we quote — garages, extensions, dormers, and whole-property flat roofs all fall into this category, and the price range is wide enough that a single “average cost” figure isn’t much use on its own. Here’s what actually makes up the price, and where your money goes.
Typical flat roof replacement costs
| Covering type | Typical cost (garage/extension) | Cost per m² |
|---|---|---|
| GRP fibreglass (our recommended system) | £2,500–£4,500 | £65–£95 |
| EPDM rubber | £2,800–£5,000 | £70–£100 |
We don’t install new felt roofs. If you’re seeing felt quoted elsewhere at a lower £1,800–£3,500 range, that’s a genuinely different, shorter-lived product — see our full guide comparing GRP, EPDM and felt for why we made this call.
These figures are for a straightforward, accessible roof of typical garage or single-storey extension size. Larger flat roofs, complex shapes, or difficult access will move these numbers upward.
What’s actually included in that price
Strip-out and disposal. Removing the old covering — and, on some older properties, dealing with what’s underneath it — plus skip hire and waste disposal.
Deck inspection and repair. The timber decking beneath the covering sometimes has rot or water damage that only becomes visible once the old covering is off.
Insulation. Current Building Regulations generally require insulation to be brought up to modern standards when a flat roof is replaced. See our guide to warm roof vs cold roof for what this means in practice.
The covering itself. GRP or EPDM, plus the labour to install it correctly — laps, upstands, and edge trims done properly are what determine whether a flat roof lasts 20 years or 40.
Building Control sign-off. Included as standard in our pricing — not an optional extra. See our full guide on Building Control sign-off.
Why some quotes look suspiciously cheap
If one quote is significantly lower than the others, it’s worth checking specifically:
- Is it actually GRP or EPDM being quoted, or is it felt priced to look competitive against a longer-lasting system?
- Is insulation upgrade included, or is it a like-for-like recover that may not meet current regulations?
- Is Building Control sign-off included?
- What’s the guarantee, and who’s backing it?
See our full guide on why roofing quotes vary for how to compare properly.
Garage and extension roofs specifically
These are some of our most common flat roof jobs, and costs are usually at the lower end of the ranges above simply due to size — access is the other big variable, since scaffolding needed for a hard-to-reach garage roof adds to the total in a way a simple ladder or tower setup doesn’t.
The ranges above are a genuine starting point, but the only way to know what your specific flat roof will cost is a site visit — we’ll check the deck condition, measure accurately, and give you a written, itemised quote with nothing hidden.
Not sure what your roof needs?
We offer free surveys across Merseyside. We go up, take photos, show you what we find and give you an honest recommendation. No pressure, no obligation.