Flat Roof Replacement Cost UK: 2026 Price Guide

How much does a flat roof cost to replace?

Most UK homeowners pay somewhere between £1,500 and £4,500 to replace a flat roof, depending on size, the covering you choose and whether the deck underneath needs work. A small porch or garage roof sits at the bottom of that range; a large flat-roofed extension at the top.

Here is what the different systems actually cost, how long each lasts, and where quotes usually differ.

Flat roof replacement cost by size

Typical UK flat roof replacement costs (2026)

Roof	Area	Typical cost
Porch or bay	5–10 m²	£700 – £1,400
Single garage	15–20 m²	£1,400 – £2,600
Double garage	30–35 m²	£2,200 – £4,000
Rear extension	20–30 m²	£1,900 – £3,800
Large extension / dormer	40–50 m²	£3,200 – £6,000

Includes stripping the old covering, waste removal and the new system. Add £400–£900 if the timber deck needs replacing, which you only find once the old covering is off.

The four systems, and what they cost

High performance felt

£50 – £80 per m² · 20–25 years

Torch-on felt in two or three layers. The modern version is nothing like the bitumen roofs people remember failing — properly laid, it is a long-life system at a sensible price.

EPDM rubber

£70 – £110 per m² · 30–50 years

A single rubber membrane, usually in one piece with no seams across the field of the roof. Very few failure points, and it copes well with movement in the deck.

GRP fibreglass

£80 – £120 per m² · 25–30 years

Laid wet and cured in place, giving a hard seamless finish. Good where the roof is walked on. Needs dry weather to install and a stable deck, as it does not flex.

Single-ply membrane

£80 – £130 per m² · 30+ years

Hot-air welded sheets, more common on commercial work. Worth considering on large or complex flat areas where felt would need a lot of joints.

Our flat roofing and felting page covers what is involved on each.

What the price actually includes

• Stripping the old covering and getting it off site — usually a skip
• Deck inspection and repair — soft or rotten boards have to come out
• Firrings or tapered insulation if the roof does not currently drain properly
• The new covering, plus primer where the system needs it
• Upstands and detailing at every wall, kerb and abutment — this is where most flat roofs actually leak
• Trims and outlets, new drip edges and a working gutter connection
• Access equipment — usually a tower rather than full scaffold

The upstands and outlets are what separate a flat roof that lasts twenty years from one that leaks in three. A quote that only prices the covering is not pricing the job.

Why quotes differ so much

Deck condition. Nobody can see the boards until the old covering comes off. An honest quote will tell you the price assumes a sound deck and give you a rate for replacing it if not.

Insulation. If the roof is over a heated room, Building Regulations require insulation to current standards when you replace the covering. That adds cost, and a quote that ignores it is understating the job.

Falls. A flat roof is never truly flat — it needs a slope to drain. If yours is ponding water, fixing the falls costs more than simply re-covering and leaving the problem in place.

Detailing. A simple rectangle is cheap. A roof with three abutments, a chimney and two rooflights is not.

Repair or replace?

A localised split or a failed upstand can often be repaired for £200–£600. That is worth doing if the rest of the covering is sound and the roof is under ten years old.

Replace when the covering is blistered or cracked across the whole area, when water is ponding and not clearing, when the deck feels soft underfoot, or when you have patched the same roof more than twice. Our roof repairs page covers the smaller jobs.

How long should a flat roof last?

Expected lifespan by system

System	Expected life
Old-style pour-and-roll felt	10 – 15 years
High performance torch-on felt	20 – 25 years
GRP fibreglass	25 – 30 years
EPDM rubber	30 – 50 years
Single-ply membrane	30+ years

Do you need planning permission?

Replacing a flat roof like for like is normally maintenance and needs no planning permission. Building Regulations do apply though: if you are replacing more than 25% of the covering on a roof over a heated space, the insulation has to be brought up to current standards. Changing the shape of the roof, or converting it to a terrace, is a different matter and needs checking with the council.

Getting a price for your roof

We survey flat roofs across Gosforth, Jesmond, Kenton, Heaton and the wider North East, tell you whether it needs repairing or replacing, and put a fixed price in writing. See examples of our recent work — including a garage roof re-felt in Fawdon — or read more about the company.

Flat roof needs replacing?

Survey, honest advice, fixed price in writing. Gosforth, Newcastle and the North East.

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