How Much Does a Flat Roof Replacement Cost?

Replacing a flat roof typically costs from around £1,200 for a felt roof on a single garage to £9,000 for a 50 square metre roof priced with everything included. The exact price depends on the size of the roof, the materials you choose and whether the timber structure underneath needs replacing. Getting a realistic budget means understanding what goes into a proper quote and what gets left out of a cheap one.

Typical flat roof replacement costs at a glance

When you ask a roofing company for a price, they will usually quote for the complete job. This includes the new surface, the labour to install it, removing the old roof and basic access equipment. It is helpful to look at these complete installation costs before breaking down the price by material.

The Federation of Master Builders provides a flat roof replacement cost guide with all-in installation ranges based on the total size of the roof. Labour is around 40 per cent of the total cost.

The table below shows total installation costs based on the size of your roof.

These are typical published figures for 2026, and local quotes will vary depending on where you live and the condition of your property. Prices are generally higher in London and the South East.

Cost per square metre by material

Roofers price most of their work per square metre. The material you choose for the new surface will change the price significantly. You have five main options for a modern flat roof covering.

Built-up felt is usually installed as a torch-on system using a blowtorch to melt the layers together. It is the cheapest option but has the shortest lifespan. EPDM rubber is often laid as a single sheet and glued down, which means few or no seams for water to get through.

GRP fibreglass is painted on as a liquid resin over glass fibre matting before curing into a hard, seamless surface. Single-ply membranes are similar to rubber but use different plastics and are often heat welded at the seams. Liquid systems are painted directly onto the roof and are particularly useful for roofs with complex shapes.

The table below shows the cost per square metre and expected lifespan for the most common flat roof materials.

These are typical published prices for 2026, and local quotes will differ. If you are unsure which option is right for your property, you can read our guide to see if a rubber roof is better than felt or fibreglass before you make a decision.

What a garage or extension roof usually costs

Most homeowners are looking to replace the roof on a single garage, a dormer window or a typical home extension. The material prices above translate into predictable ranges for these common jobs.

A single garage is usually between 15 and 20 square metres. A basic felt roof for a garage of this size will cost between £1,200 and £2,000. An EPDM rubber roof will cost between £1,500 and £2,600. A GRP fibreglass roof is the most expensive option at £1,800 to £3,000.

A typical home extension is larger, usually between 20 and 40 square metres. A felt roof on an extension of this size will cost between £1,800 and £3,500. Upgrading to EPDM rubber will cost between £2,200 and £4,500. Choosing GRP fibreglass pushes the price to between £2,800 and £5,500.

These totals are lower than the all-in figures in the first table because published prices do not all cover the same things. Some include new decking, insulation and access, while others price the new covering only. The cheap quote is often the one that leaves those essential extras out.

What pushes the price up

The surface material is only one part of the total cost. Several other factors will increase the final bill, and a good roofer will inspect the roof carefully to check for them.

The timber deck on a flat roof is the layer of structural boards that the waterproof surface sits on. Nobody can see rotten timber until the old covering is taken off. If the deck is soft or damaged by a long-term leak, it must be replaced before the new surface goes down.

Adding warm-roof insulation typically adds £15 to £35 per square metre. A warm roof has insulation placed above the timber deck, keeping the structure warm and reducing the risk of condensation. A cold roof has the insulation placed between the joists underneath the deck.

Access equipment is another major cost driver. Scaffolding is often a separate and significant line on your final bill. A single-storey garage might only need simple staging, but a two-storey extension or a dormer window will require full scaffolding to keep the workers safe.

Details around the edge of the roof also add to the cost. Parapets are small walls at the edge of the roof, and upstands are where the roof covering turns up against a higher wall. Both require careful detailing and extra materials to ensure they are fully watertight.

What a proper quote should cover

A vague one-line quote is a warning sign. You need to know exactly what you are paying for and what happens if the roofer finds a problem once they start work.

A quote is a fixed price that cannot change unless you agree to extra work. An estimate is just a guess and can increase significantly by the end of the job. You should always insist on a written, itemised quote.

A proper written quote will list the following things clearly.

• The exact material being used for the surface.
• How much it will cost to replace the timber deck if it turns out to be rotten.
• Whether scaffolding or other access equipment is included in the price.
• The cost of upgrading the insulation if required by building regulations.
• Whether waste removal and skip hire are included.
• Whether VAT is included in the final total.
• A clear schedule of staged payments.

Repair or replace?

You might not need a full replacement if the damage is minor and the rest of the roof is in good condition. A small patch repair can keep the weather out while you save for a complete new roof.

Small repairs are usually charged at a fixed price or a day rate. If a single seam has split on an otherwise sound felt roof, a roofer can clean the area and apply a patch or a liquid repair coating. You can learn more about roof repair costs and what to expect from a roofer if you think a simple patch is enough.

Replacement is the honest answer when the material has reached the end of its natural life. If a felt roof is at or beyond its expected lifespan, the covering is likely to have become brittle. Patching one crack will not stop another appearing nearby. Replacement is also the likely answer if water has been getting in for a long time, as trapped moisture can rot the timber deck and the joists underneath.

Because a flat roof has very little slope, water sits on the surface for longer than on a pitched roof, so it relies on a fully sealed covering over a sound timber deck.

Insulation and building regulations

Replacing a flat roof is not just about keeping the rain out. In many cases, it involves strict legal rules about energy efficiency and structural safety.

In England, repairing or re-covering a roof does not normally need a building control application if less than 25 per cent of the building envelope and less than 50 per cent of the roof is affected. The Planning Portal confirms that a building control application is normally needed once 50 per cent or more of the roof is affected.

If you are replacing the whole roof, approval is needed. The Planning Portal says that re-covering a roof should include improving its thermal insulation. If a roof with integral insulation is replaced, you may be required to upgrade this thermal element to meet modern standards.

Approval is also needed for structural alterations, where a new covering performs significantly differently in fire, or where it adds 15 per cent or more to the weight.

You do not always have to apply to the council yourself. CompetentRoofer is a government-authorised competent person scheme run by the National Federation of Roofing Contractors. Registered roofers can self-certify roof refurbishment in England and Wales. The customer should receive a building regulations compliance certificate when the job is finished.

Otherwise, the work must go through council building control or a registered building control approver. Rules differ in Scotland and Northern Ireland, so you should check with your local council rather than guessing.

How long the job takes

A flat roof replacement is usually a fast project, but the weather can cause delays. A good roofer will wait for a dry spell before removing your old roof to protect the inside of your home.

A small roof takes two to three days to complete. An average-sized roof takes up to a week. The exact time depends on how easy it is to access the roof and whether the timber deck needs replacing.

Because nobody can see the condition of the structural timber until the old felt is removed, you should plan for unexpected costs. It is sensible to keep a 10 to 15 per cent contingency fund ready just in case the deck boards are rotten.

Guarantees and paperwork to ask for

A new roof is a major investment, and you need the right paperwork to prove it was installed correctly. This is especially important if you plan to sell your home in the future, as buyers will ask to see the certificates.

Under the Consumer Rights Act 2015, work must be done with reasonable care and skill. If it is not, you can ask for it to be put right or for your money back. If you have a dispute with a tradesperson, Citizens Advice is the best place to get guidance on enforcing your rights.

You should always check what kind of guarantee the roofer is offering. A personal guarantee from the builder is worthless if the firm folds next year. You want an insurance-backed guarantee, which means an independent insurance company will honour the warranty even if the roofing firm stops trading.

Paying by credit card gives you Section 75 protection on purchases over £100 and up to £30,000. This means the credit card company is jointly liable if something goes wrong. Contracts agreed at home, by phone or online normally carry a 14-day cooling-off period, but if you ask for work to start inside that period you must pay for what has been done.

You should also check the TrustMark register. TrustMark is the government-endorsed quality scheme for work in and around the home. Membership is a good sign that the firm is professional, though it is not a guarantee of perfect work.

How to compare flat roof quotes

Finding a reliable tradesperson means doing a little research and refusing to be rushed. You should gather three written quotes to get a clear idea of the going rate in your area.

Compare the quotes side by side. Check if they all include the same materials, the same access equipment and the same waste removal. If one quote is significantly cheaper than the others, it is often because it leaves out the scaffolding, the deck repairs or the insulation upgrade.

You must watch out for common mistakes and scams in this trade. Be very wary of the following warning signs.

• Cold callers who knock on your door claiming they have spotted a loose tile or moss from the street.
• Pressure from the salesperson to decide today or sign a contract immediately.
• Tradespeople who demand cash only or ask for a big deposit before materials arrive.
• Roofers who have no physical business address and only provide a mobile phone number.
• Firms making roof coating and painting claims, or selling pressure washing as maintenance.

Some bad roofers will try to sell you a whole new roof for a local fault that could easily be patched. If you suspect someone is not being honest, our guide on how to spot a dodgy roofer before it costs you will help you protect yourself.

Common questions

What is the cost of replacing a flat roof?

The cost of replacing a flat roof is typically between £2,800 and £3,600 for a 20 square metre area, rising to between £7,000 and £9,000 for a 50 square metre area. The final price depends heavily on the material you choose and whether the timber deck underneath needs replacing. Prices will also increase if you need full scaffolding or if you must upgrade the insulation to meet building regulations.

How much does a leaking flat roof repair cost?

A leaking flat roof repair is usually charged at a day rate or a fixed price for a small patch. If a single seam has split, the repair will be relatively cheap and fast to fix. However, if the leak has been happening for a long time, the timber underneath may be rotten, which turns a small repair into a partial roof replacement.

Do flat roof installation rules apply to conservatories?

Yes, if you are replacing a glazed or polycarbonate conservatory roof with a solid flat roof, building regulations will apply. Adding a solid roof takes the conservatory out of its exemption. Building control will want to see that the existing structure can safely carry the new roof and that the new roof meets energy efficiency standards.

Can I replace my flat roof myself?

You should never attempt torch-on felting, structural timber replacement or working at height yourself. Professional roofers have the correct safety equipment, training and insurance to do the job safely. A poorly installed flat roof will leak, trap condensation and fail building regulations, costing you much more to put right later.

Next steps

Before you hire a roofer, make sure you are completely prepared. A methodical approach will protect your home and your money.

• Take photos of the leak or the damaged roof from the ground or from inside the loft to show the roofer.
• Ask three different companies to inspect the roof and provide a detailed, itemised written quote.
• Check that the quote includes waste removal, VAT, scaffolding and a price for replacing rotten timber.
• Ask the roofer for proof of their public liability insurance and check if they offer an insurance-backed guarantee.
• Check if the firm is registered with the CompetentRoofer scheme so they can self-certify the building regulations.
• Agree a staged payment plan and only make the final payment when the job is completely finished and the site is clear.

Now that you know what a proper quote should look like and what rules apply, you are ready to find a roofer near you to get your flat roof inspected and priced.