More UK homes have flat roofs than many people realise. They are common on extensions, garages, dormers, bay windows and porches. Flat roofs seem fairly simple but prices can vary quite a bit depending on material used.
Although the design and structure of the roof usually has the biggest impact on the cost of a pitched roof, the size of the roof and the type of covering you choose usually has the biggest impact on the cost of a flat roof.
This guide explains the average cost of replacing a flat roof in the UK, with prices for materials, extra costs to look out for and what really happens during the replacement process.
The average flat roof replacement cost in the UK is between £1,500 and £7,500 for most properties. This comes in at an average cost of around £75 per m² installed.
Sometimes small projects like a garage roof or porch roof can cost less than £1,500. Larger extension roofs or premium options like GRP fibreglass can push costs into the upper end of the range.
The most important factor is almost always the material you pick. A basic felt roof can help keep the initial cost down but other options such as fibreglass or good quality rubber membranes are more expensive but tend to last much longer.
Once you know the roof size and the material you want, flat roof replacement is one of the easier jobs to estimate.
The covering itself is the primary cause of variation in flat roof prices. A cheaper material may save you money up front but a more durable option might be a better bet for the life of the roof.
| Material | Installed cost (per m²) | Typical lifespan |
|---|---|---|
| Felt (torch-on or traditional) | £40 to £80 | 10 to 20 years |
| EPDM rubber | £50 to £100 | 25 to 40 years |
| GRP fibreglass | £80 to £130 | 25 to 40 years |
| PVC / single-ply membrane | £60 to £110 | 20 to 35 years |
Felt roofing is still the cheapest and is still commonly used on smaller roofs especially garages. It is attractive because it costs less to install, but it usually has to be replaced sooner than other materials. Repeated replacements over several decades can sometimes make it less cost effective.
EPDM rubber roofing has become a popular option for residential flat roofs. It strikes a good balance between price and lifespan. It is usually laid in one large sheet which means there are less joints to get through and so it becomes more durable.
GRP fibreglass roofing is the top of the line option to choose. It offers a strong and seamless finish and is often used in high usage or high wear areas such as balconies or roof terraces. Installation is more expensive and the weather has to be right for fixing but the final surface is very tough.
Larger buildings are more likely to have PVC or single-ply membranes, but these are also used on some homes. They are light weight, flexible and may perform effectively where these characteristics are important.
A flat roof replacement generally includes taking out the existing covering, inspecting the structure underneath and then installing the new roofing system. The exact process will vary depending on the material being laid but the major steps are usually the same.
- Remove the old roofing
The existing roof surface is stripped off first. This could be a piece of old felt, EPDM rubber or some other type of flat roof membrane. All has to come off so the roofer can see what’s underneath. - Inspection of roof decking
Once the old covering is removed away, the decking can be inspected thoroughly. This is one of the areas where costs can change during a project. - Water that has been getting through the old roof can damage the boards below especially if it's OSB or plywood. If they are rotten or damaged they have to be replaced before putting on the new covering.
- Adding or upgrading insulation
Flat roof replacement normally includes insulation. If the work is regulated by Building Regulations you may need to improve the insulation. Even if it is not a requirement, adding insulation can make the room below more comfortable and help to reduce heat loss. - This is another reason why the final quote can be higher than an initial estimate, as the condition of the existing roof isn’t always clear until the contractors remove the old covering.
- Installing the new roof covering.
The installation method depends on the material you choose. Felt roofs are mostly assembled in layers and joined together using heat. EPDM rubber is applied as a single sheet and is secured down. GRP fibreglass is a liquid system that cures to a tough waterproof finish. - Finishing the edges and details
It's often the smaller details that make the greatest difference to the expected lifespan of a flat roof. The areas where the roof meets walls, windows and the edge of the building needs to be properly sealed and finished. - Good detailing around these areas helps prevent water getting under the new covering and is often the difference between a long lasting roof and one with early problems.
There are a few things that can impact the final price of a flat roof replacement. The size of the roof matters but it's not the only thing.
Roof size
Most roof quotes are calculated in the square metre price. Generally larger roofs are cheaper per m² as fixed costs such as set up and labour are distributed over a larger area.
For instance a 30m² extension roof will not usually run you twice the cost of a 15m² garage roof. The bigger projects tend to work out slightly cheaper per square metre.
Roof access
Easy access keeps cost down. Garage roofs that you can be access from ground level are usually pretty straightforward.
If you need a rear extension roof that requires scaffolding or has limited access, it will cost more considering that it takes more time and equipment to do it safely.
Deck condition
One of the major unknowns is the overall state of the boards beneath the roof. Decking can have leaks and rot and replacing it adds extra materials and labour. This is why some quotations will vary when the old roof covering has been removed.
Requirements for insulation
It adds to the cost but can be a nice add-on. Based on the type and size of the project, Building Regulations might require insulation upgrades as part of the works.
Even when not required, better insulation can create better living conditions and reduce energy costs.
Roof features
Additional features increase the price. Skylights, roof lanterns, odd shapes and detailed edges all take longer to fit than a simple flat roof area.
Location
Labour prices differ across the UK. The cost of roofing work in London and the South East is normally higher than in many other parts of the country due to higher operating and labour costs.
In England and Wales, if you are replacing a flat roof exactly the same way as it was before then you don't not need planning permission. Replacing the existing covering with a similar material is generally considered maintenance work instead of a major change to the property.
Things may look different if you make modifications to the roof structure. For example, converting a flat roof to a pitched roof is a much bigger job and could require planning permission as well as Building Regulations approval.
If you are just replacing the existing flat roof covering, you will normally not need permission. If you are unsure about your own project then check with your local authority before starting work.
The biggest portion of the quote is usually the main roof covering but there are other costs that could impact the final price.
Replacing damaged decking
You have to remove the old covering to see if there are any rotten or water-damaged boards under the roof. Replacement will add to the total cost if necessary.
Insulation upgrades
Some quotes include insulation, and some do not. If insulation needs upgrading or you decide to improve it as part of the work then you should expect the price to increase.
Edge trims and finishing work
The edges of a flat roof are important for keeping water out of the roof. When you are getting quotes, make sure to see if it includes trims, flashing and other finishing work.
Scaffolding
Not every flat roof requires scaffolding. Without it you may be able to climb onto a single-storey garage roof but a flat roof on a rear extension of two-storey house will need additional access tools.
Please note that prices on this platform are typical estimates based on current UK roofing costs. These are not fixed quotes as all flat roofs are different.
The actual cost will depend on the size of your roof, the condition of the existing roof, the material you choose and whether any additional work is required once the old covering is removed.
So the best way to get an accurate figure is to have your roof assessed by a professional.
Tell us about your project using the calculator and enquiry form on this site. We'll connect you with local roofing companies that will give you a detailed estimate based on your actual roof, with no obligation to proceed.