Flat Roof Replacement Cost UK 2026: EPDM, GRP and Felt Compared

Flat roofs sit over garages and kitchen extensions across the UK, as well as porches and dormers. When one starts to leak, the flat roof replacement cost depends on two things you can see and one you cannot. You can see the size of the roof and the covering you choose. You cannot see the deck under the old felt until it comes off.

This guide sets out typical UK prices for 2026. Each price and lifespan was checked against at least two published UK cost guides. It covers the three coverings most roofers offer, typical totals for a garage and an extension, and the extras that decide the final bill.

Flat Roof Replacement Cost per Square Metre

These are typical prices to strip the old covering and fit a new one, with labour and materials included. They are researched 2026 estimates from published UK cost guides, cross-checked, and meant to help you read a quote rather than replace one.

The ranges overlap because the guides measure slightly different jobs. Some include a basic strip-off and new trims. Others price the covering alone. A quote that gives a rate per square metre and states what it covers is easier to compare than a single total.

A small roof costs more per square metre than a big one. The roofer still has to load the van, set up and finish the edges, however small the job. That is why a porch can cost nearly as much as a garage.

Flat Roof Cost for a Garage or Small Extension

Most flat roofs on houses fall into two sizes. A single garage is usually around 15 to 20 square metres. A single-storey kitchen or rear extension is often 25 to 30.

These totals assume the deck underneath is sound. If the old roof has leaked for a long time, some of the deck may need to go, or even the whole of it. That cost is covered below.

Access is rarely a big line on a flat roof. Most garages and single-storey extensions can be reached from a ladder or a small tower. A flat roof on a two-storey back addition or a dormer is different, and scaffold may then appear on the quote.

EPDM Roof Cost and What You Get

EPDM is a synthetic rubber membrane. On a house roof it usually goes down as a single sheet, glued to the deck, with trims round the edges. Because there are few or no joins across the middle, there are few places for water to find a way in.

At £60–£100 per square metre, it sits between felt and GRP on price. Several 2026 guides now treat it as the standard choice for a domestic flat roof. It copes well with cold weather and with the small movements a timber deck makes through the year.

The weak points are the edges and anything that passes through the roof. A poorly fixed trim, or a badly sealed pipe or roof light, is where most EPDM leaks start. It is also softer underfoot than GRP. It will take foot traffic for maintenance, but it is not meant as a terrace.

GRP Roof Cost and What You Get

GRP stands for glass reinforced plastic. The roofer lays glass fibre matting on the deck, soaks it in resin, and finishes it with a coloured top coat. It sets hard as one solid skin.

At £80–£130 per square metre, it is usually the dearest of the three. You pay for a hard, walk-on finish that suits small balconies and roofs people step onto. It also looks neat, with moulded trims at the edges.

GRP has two conditions. It has to be laid on a dry day, because damp spoils the resin as it cures. And it needs a firm, sound deck. If the boards flex, the hard skin can crack along the joints. A good GRP quote will say what deck the roofer plans to lay under it.

Felt: Cheapest to Fit, Soonest to Replace

Felt is the old standard on garages and extensions. Modern felt roofs use layers of bitumen sheet, often torched on with a gas flame. At £40–£75 per square metre, it is the cheapest covering to fit.

The catch is life span. A felt roof typically lasts 10 to 15 years. In that time an EPDM or GRP roof is often less than halfway through its life. Over 30 years, felt may need replacing twice, and each time you pay for the strip-off and the waste again.

Felt still makes sense in a few cases. It suits an outbuilding you do not plan to keep for long, or a budget that cannot stretch further this year. For a garage or extension you plan to keep, most guides now point to EPDM or GRP as better value over time.

Liquid Coatings: a Stopgap over a Sound Roof

Some firms offer a liquid coating instead of a new roof. It is painted or rolled over the existing covering in one or more coats, with no strip-off. Guides put it at about £60–£80 per square metre, with a typical life of 20 to 25 years.

The appeal is speed and less waste. The risk is what lies underneath. A coating seals the surface, but it does nothing for a wet or rotten deck. Laid over a roof that is already soft, it can trap the damp and hide the problem until it is worse.

A coating is worth thinking about when the deck is firm and dry and the old covering is only worn on the surface. If there is any doubt about the deck, a full strip-off lets the roofer see it and fix it.

How Long a Flat Roof Replacement Takes

Most garage and small extension roofs take two to four days once the materials are on site. The first day is usually strip-off and deck repairs. The covering and trims follow.

Weather sets the pace more than size. GRP needs dry conditions to cure, and nobody lays glue or torch-on felt in heavy rain. A roofer who books a flat roof in a wet spell may leave a temporary cover on for a day or two. That is normal, and a good roofer will tell you in advance.

Worked Example: a Single Garage Roof, Re-Decked and Re-Covered

Take a single garage of about 16 square metres, with an old felt roof that has blistered and a deck that feels soft underfoot. That is a common picture on 1970s and 80s estates, including Peterborough's New Town townships, where rows of flat-roofed garages were often built alongside the houses. The figures below come only from the tables on this page.

• New deck, all 16 square metres at £18–£30: about £290–£480.
• EPDM at £60–£100 per square metre: £960–£1,600, so with the new deck about £1,250–£2,080.
• GRP at £80–£130 per square metre: £1,280–£2,080, so with the new deck about £1,570–£2,560.
• Felt at £40–£75 per square metre: £640–£1,200, so with the new deck about £930–£1,680.

On a roof this small, real quotes often land at or above the top of those sums, because a small job still carries a full day's set-up and edge detailing. That is why the typical single-garage total in the table is £1,500–£2,400 for EPDM or GRP. Over 30 years the felt option may need doing twice, which wipes out its lower price. Our notes on garage roofs cover when a blistered felt roof is past patching.

When the Deck Has to Be Replaced

The deck is the layer of boards the covering sits on. It is usually chipboard, plywood or OSB board. When water gets through the covering, the deck soaks it up and starts to rot.

There are a few signs the deck has gone:

• The roof feels soft or springy when someone walks on it.
• Water sits on the roof for more than 48 hours after rain.
• Damp keeps coming back inside after the covering has been patched.
• Blisters or splits cover more than 20 to 30 percent of the surface.

Replacing rotten deck boards adds roughly £18–£30 per square metre. On a single garage that can mean a few hundred pounds. Nobody can know how much deck needs to go until the old covering is off, so a fair quote gives a rate per square metre for new boards and says who decides.

Standing water has its own fix. If the roof has too little fall, the roofer can lay tapered timbers called firrings under the new deck, so rain runs to the gutter. One guide prices this at £150–£400.

Patch It or Replace It

Not every leaking flat roof needs replacing. A small split or one failed joint on an otherwise sound roof can be patched, usually for £200–£600. That is worth doing when the rest of the covering is in good shape and the deck is firm.

Replacement becomes the better buy when the faults are spread out. A felt roof near the end of its 10 to 15 years, with blisters across much of it, will keep leaking in new places. Each patch costs a call-out, and none of them fixes the deck.

A useful test is to ask the roofer how long they will guarantee the patch. If they will not stand behind it for more than a season, they are telling you the roof is close to the end. Ask for the patch price and the replacement price on the same visit, so the choice is made on real figures rather than guesswork.

Insulation, Building Regulations and Your Flat Roof Replacement Cost

A flat roof over a heated room, such as a kitchen extension, is part of the home's heat loss. When most of it is replaced, the Building Regulations usually expect the insulation to be brought up to current standards under Part L. On a flat roof that often means a warm-roof build, with insulation boards laid on top of the deck and the new covering over them.

That adds to the price, and it can raise the roof edge by the thickness of the boards. One guide lists the insulation upgrade at £250–£600 on a small roof. A garage that is not heated is usually a different case, as it has no heated room below.

Ask each roofer whether they plan to insulate, and who will deal with Building Control. A quote for a kitchen extension that leaves this out is not complete.

Comparing Two Flat Roof Quotes Line by Line

Put the quotes side by side and check each one covers the same work.

• The covering by name, with its thickness or system.
• Strip-off and waste. One guide puts skip hire at £150–£350.
• The rate for replacing deck boards if rot is found.
• Firrings, if water sits on the roof now.
• Edge trims and upstands, plus how the roof meets the wall.
• Insulation, if the room below is heated.
• The guarantee, and whether it covers the materials as well as the labour.
• Whether VAT is included.

A low price that leaves out the deck rate or the trims is not the cheapest quote. It is an unfinished one.

Our Verdict: Flat Roof Replacement Cost This Year

For most garages and small extensions, EPDM or GRP gives the best value in 2026. Expect £60–£130 per square metre fitted, or about £1,500–£2,400 for a single garage. Felt is cheaper to fit but often needs replacing twice as soon. The flat roof replacement cost that surprises people is the deck, so ask every roofer for a per-metre rate for new boards before you compare totals.

Getting a Quote in Peterborough

We are not roofers and we don't fit flat roofs. We are an enquiry service: tell us the size of the roof and what it is doing, and we pass your enquiry to an independent local roofing firm covering your part of Peterborough, who quotes you direct. We don't inspect or approve the firms we pass enquiries to, so read how to choose a roofer before you sign anything. Our flat roofing page explains how garage and extension roofs are usually handled, or you can get a quote now.