Flat Roof Replacement & Repair Costs

Last updated 29th July 2020

Want to know how much it costs to repair or replace a flat roof? In this article we provide a breakdown of prices for both repairing and replacing flat roofs. This includes the cost for materials, labour and a cost per square metre, allowing for easy calculations so that any homeowner can determine an estimate for their job.

The most common type of flat roof that needs replacing or repairing is a garage roof. For a single garage roof replacement, you're looking at around £700 to £1000 with the price increasing by around 50% for a double garage. The main component that will affect the cost of a new flat roof is the material it's made from. For example, felt roofs are very cheap when compared to lead or fibreglass. Keep reading to find out what else can affect the overall cost and how you can keep costs down.

replacing a flat roof

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How Much Does It Cost to Replace or Repair a Flat Roof?

No matter how professionally a flat roof is fitted, there will come a time when it begins to fail, leaking at first, but eventually bowing in and in danger of collapse. When you see signs of leaking, you should consider repairing or replacing the roof, putting things off will not fix the problem, but will make it worse and more expensive! As to whether you should repair or replace the roof, that depends on the roofing material and the amount of damage. Funnily enough flat roofs are generally built with a slight incline to allow rainwater to drain off into gutters, so basically most flat roofs aren’t actually flat!

The average cost of replacing a flat roof is usually in the range of £700-£1,300 depending upon what materials the roofer uses, whether or not scaffolding will be needed, and the size of the roof. There are numerous flat roof applications which have varying costs, including:

  • Felt roof (£40 to £60 per m2)
  • Rubber roof (£80 to £85 per m2)
  • Fibreglass roof (£70 to £90 per m2)
  • Lead bay roof (£90 to £105 per m2)
  • Fibreglass bay roof (£95 to £120 per m2)

Most roofers operate in pairs and will typically charge around £200-£300 per day. Usually, the job will be completed within a single day, and the roofer should always come back the next day to ensure there are no leaks.

Repairing or Replacing Flat Roof Prices

Here are a few average costs for replacing a flat roof:

Job Size Scaffolding? Avg. Cost Duration
Single Garage No £700 1 day
Double Garage No £900 1 day
2-storey Extension Yes £1,200 1.5 days


Here is a breakdown of the different roof materials and their costs:

Roof Type Average Cost Per m2
Felt roof £40-£60
Rubber roof £80-£90
Fibreglass roof £70-£90
Lead bay roof £90-£105
Fibreglass bay roof £95-£120


Supply Costs

If you want to take the DIY route, then you will only need to calculate the supply costs. Doing it yourself could help you save a significant amount, especially If you’re planning to replace a roof on a 2-storey extension, as this will allow you to save around £300.

Replacing a Flat Roof

Roof Material Average Cost
Felt £2 to £10 per m2
Rubber £9 to £12 per m2
Fibreglass £2 to £3 per m2
Lead £2 to £4 per kg
Fibreglass insulation £6 to £10 per m2
PIR Insulation boards £5 to £15 per m2
Spray foam insulation £5 to £12 per spray can


Repairing a Flat Roof

If your roof is in fairly good condition, it may only require repairs. Here is a breakdown of the material costs for repairing a flat roof:

Roof Material Average Cost
Base layer £40
Mid layer £80
Top layer £200
Rubber membrane £220
Adhesive and Sealant £50
Edgings and drip edge £140
Resin £200
Tissue £30
Topcoat £130
Trims and baton £130
OSB boards £100
Clay £50


Cost Breakdown Calculator

Individual costs for replacing a flat roof on a 2-storey extension - Total Cost: £1,200

50%

Materials
£600

25%

Tradesmen
£300

25%

Scaffolding
£300

Labour Costs and Time Frames

Individual roofers typically charge around £25 per hour, although this will depend on the work being done. They usually only charge around £18 per hour for roof repairs. A lot of roofers work in pairs and will typically charge around £200-£300 per day.

Replacing a roof will take much more time, with the standard duration for the removal and replacement of a single garage roof takes around 7 to 8 hours. A garage roof replacement cost, including labour, will, of course, vary depending on the type of roof you choose. For example, labour for a felt, rubber or fibreglass roof costs around £300 for two tradesmen, although some roofers charge up to £55 per square metre.

What Does Replacing a Flat Roof Entail?

Flat roofs are made up of roofing timbers or joists which are laid across walls at a specified distance apart; then they are covered with some sort of boards or sheeting that usually need to be waterproofed. There are many different types of flat roof materials, although EPDM or rubber and fibreglass are the most popular types.

When replacing a flat roof, it makes sense to fit new fascia boards at the same time, as these will have to removed anyway, so you are already paying the labour for half the job anyway! In addition, a flat roof that has been leaking may also need the roof joists themselves treated or even replaced if they are damp and rotting. It makes no sense to fit a new roof on top of rotting joists. So a joiner or carpenter may be required, along with a decorator to finish the interior.

To help you understand the replacement process, take a look at the below guide which covers the different roof types.

Felt Roof

The first step involves using a small spade to separate the felt and the timber underlay. Fascia boards, edgings and trims will also be removed during this process.

The decking will then be measured to establish how much felt you need. The felt will then be layered onto the roof and fitted by nailing it in, making sure to leave an overlap which will protect the roof from adverse weather. The felt may also be secured with adhesive and drilled in fascia boards.

Rubber Roof

To remove rubber roofing, a professional roofer will typically use a utility knife to cut the material into small pieces ready for disposal. A heat gun may also be used to get rid of the membrane section by section.

rubber roof

The rubber material will then be measured and applied to the roof using a strong adhesive which will ensure the rubber is secure and will last a long time.

Fibreglass Roof

If your fibreglass roof is falling apart or damaged, then it will need to be removed before replacing it. The roof material should come away easily with the help of a shovel, although some force may have to be applied if it is not loose.

Once the existing roof has been removed, and the decking and laminate trims are in place, the edges should then be bandaged to keep everything in place. The material will then be measured and laid out onto the roof. Once everything is in line, the resin will then be applied to wet the decking then lay out the material. Another resin layer should then be applied to secure it onto the roof.

Lead Roof

To remove lead material, your tradesmen will use a diamond-tipped small angle grinder. They will go no deeper than 15 to 20 mm and will tend to use a screwdriver to remove the tiles thoroughly.

The lead will then be measured, laid out and slightly onto the top of your roof. Rolled up lead should then be hammered between the brickwork and the wall to create a secure structure.

What Does Repairing a Flat Roof Entail?

Typically a flat roof repair job will involve essentially re-waterproofing a section of the roof, although many other repairs can be undertaken depending on the type of roof you have.

Felt Roof

If you have a felt roof, then any leaks may cause blistering. The felt repair process for this involves cleaning the surface and removing any mould. A tradesman will then use a heat gun to heat up the area where the leak occurred, making sure that they do not apply too much pressure as felt can melt easily. Once it is completely dry, the adhesive will be applied to the area, and a new piece of felt will be put in its place and secured with more adhesive.

felt roof

A similar process applies if there any splits in the material or it starts to overlap, as again this will be caused by water damage and should be repaired as soon as possible.

Rubber Roof

When repairing a rubber roof, no asphalt-based products must be used as rubber is not compatible with these materials, and if they are used, an entire replacement would be required. To avoid extra costs, a qualified tradesman will use simple household cleaners to treat the area and remove dirt, including the carbon that rubber releases over time. This must be removed to allow the new materials to stick.

EPDM roofing primer will then be used to prepare the damaged area. A pressure-sensitive patch or a glue-down path will then be applied to the area making sure that it fits exactly and does not overlap. This should then be sealed with EPDM lap sealant around the patch’s perimeter then smoothed out and secured.

Fibreglass Roof

One of the most common issues with a fibreglass roof is holes and cracks. To repair this type of damage, a disc sander will be required to clean the area and remove any damaged material, followed by a thorough cleaning of the area with acetone.

Resin and catalyst should then be mixed and applied to the affected area; then it is left to set. Once set, it should then be sanded down and levelled. Two layers should then be cut to size, with one the same size as the damaged area and one slightly smaller. Mixed resin should then be applied again before installing the fibreglass material.

To finish off the job, your chosen tradesmen will sand down the area once it is cured then apply a waterproof top coat to enable your roof to keep as long as possible.

Lead Roof

Lead roof repairs are usually conducted due to cracks caused by heat expansion of the main roof material and flashings. If left, they can lead to a significant amount of damage, despite the cracks being almost invisible on occasion.

To fix the hole or crack, your tradesman may decide to use a paint-on roof sealer. However, this may not be the best decision as it can actually make a repair job much harder. Instead, the best way to repair a lead roof is by welding a piece of lead onto the damaged area.

lead roof repar

Flashing tape can also be used to secure the roof material along with a primer which acts as an adhesive to secure the lead in place. However, this is not a permanent solution, unlike welding, which is definitely the preferred option for professionals.

Cost Affecting Factors of Replacing or Repairing a Flat Roof

There are several considerations you need to take into account when assessing roof replacement or flat roof repair costs. The most important being the type of roof you choose, as prices can vary with a felt roof repair costing an affordable £50 per square metre. Mid-range choices include rubber at £80 per square metre and fibreglass at £90 per square metre.

You may also need to consider what the roof is for, as the bigger the area you want to cover the more expensive it is. The most common roof applications include a garage roof (£1,500), porch roof (£3,000), dormer roof (£4,000), bay window (£7,000) and main roof (£10,000).

You will need to weigh up waste disposal costs when replacing or repairing materials, as the typical expense is around £100 for a tradesman to get rid of any waste.

Additional Costs

You may also want to consider the following prices before estimating your final flat roof cost:

Extra materials Average cost
Scaffolding £40 to £150 per day
Wood fibre insulation £3 to £17 per board
Polyisocyanurate insulation £4 to £35 per m2
Chipping £5 to £9 per bag
Decking board £65 to £140 per board


Can I Replace or Repair a Flat Roof Myself?

Some flat roof repairs can be done on a DIY basis; there are various waterproofing and sealant materials which are effective in tackling temporary repairs, giving you time to gather quotes and save up for long-term professional repairs. You can even buy paint on "waterproofer" which is emergency roof repair in a tin that costs around £10 per litre. You can also purchase roof repair kits which include resin, catalyst, roof material, tape and topcoat. There are many kits available for each type of roof, although the average price is around £45 for small repair kits and up to £300 for leaking roof repair kits.

To complete the job, you may also require a number of tools including:

  • Utility knife (£2 to £19)
  • Crowbar (£4 to £25)
  • Shovel (£10 to £37)
  • Nail gun (£30 to £550)
  • Heat gun (£20 to £690)
  • Hammer (£3 to £28)

If damage to the roof is localised to just a small area, a repair may be the best option, rather than replacing the entire roof. However, if you cannot fix the roof material yourself on a DIY basis, it may be more cost-effective to bring in a contractor to replace the roof completely rather than paying them for small and temporary repairs.

roof repair

In many cases making repairs to a flat roof is a complete waste of money, for example, if the roof timbers underneath are damaged, then a complete replacement is best instead of a repair. In addition, some roofing materials are difficult to patch in small damaged areas without damaging the rest of the roof, thereby making things even worse.

Does My Flat Roof Need Replacing?

While it may seem cheaper to repair your roof in the short-term, it is much better to replace your roof before you end up with extensive damage on your roof and inside your home.

You will find that some roof types will last longer than others. For example, a felt flat roof usually lasts around 10 to 15 years. While a fibreglass roof should be replaced after 20 years. A more durable material is rubber membrane has a lifespan of 40 years, although the most long-lasting of all is lead which can last as long as 60 years.

One of the main problems flat roof owners face regardless of the material is leaking, which cannot only cause leaks but will also force the timber decking to rot. If this occurs often you may need to have your roof replaced to prevent any further water damage or rot.

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Does My Flat Roof Need Repairing?

If you have noticed any water dripping from the ceiling, this could be due to a hole, split, or blister on your roof material or flashing which can be susceptible to rips. You may be able to notice this on materials such as rubber or felt; however, other materials such as lead may be more subtle.

Another common issue is water pooling, which causes a build-up of water that may cause a leak. To prevent any further damage, you should repair the issue as soon as possible.

Building Regulations

For repairs or partial replacement of less than 25% of your roof, you will not need planning permission. However, you will need to apply if you are planning to conduct the following:

  • You are replacing or repairing more than 25% which would require the insulation to be improved.
  • Carry out structural alterations.
  • The quality of the roof material will be significantly different.

If you do require planning permission, then you could anywhere between £206 to £462 depending on the extent of the roof work.

What is a Green Roof?

A green roof involves the installation of a waterproof underlay covered in grass and plants, which can also feature a drainage system that is a great way to combat flooding.

One of the main advantages of having a green roof is that it preserves water, and instead of being wasted, it is released back into the environment.

green house roof

Having a green roof installed could cost anywhere from £50 to £100 per m2 for an extensive green roof to £150 to £200 per m2 for an intensive green roof which features deeper roots for large plants. Despite the initial cost, having a green roof installed can help you reduce your energy bills, as it is one of the most energy-efficient features you can have outside your home. You can also benefit from 25% compensation for your overall costs if you install a green roof on 50% of your property.

Another benefit of a green roof it is that is great at preserving water, which is great for the environment as less water is being wasted. A green roof also has a lifespan of 50 years due to its green covering which acts as a barrier against the elements which cause rusting or mould on typical roof applications.

Flat Roof Maintenance

To prevent regular repairs or an entire replacement, you should try to look after your roof as much as possible. This involves checking your roof at least twice a year, especially when there are significant weather changes which may cause damage to your roof. Make sure to look inside as well at any potential leaks in your ceiling, as this will be an indicator of damage forming.

You should also try to remove as much debris as possible, as this will help to prevent mould or algae growth on your roof and gutters, which will also deter water pooling. To reduce the time spent on this chore, you could consider purchasing a pressure washer which can range from £70 for a basic pressure washer to £2,000 for high-quality pressure washers.

If you have any trees surrounding your home, you should try to keep on top of them by either cutting them down or trimming the trees regularly, as this will reduce the amount of debris on your roof. You may want to hire a professional tree surgeon to do this, who will charge around £120 per hour for jobs such as pollarding which will reduce foliage. However, if you want any trees removing this could cost range from £150 to £750 for small to medium trees, while large and extra-large trees could cost around £650 to £2,500.

ballast on house roof

There are many ways to preserve your roof, although this will depend on the type of material used. For example, EPDM rubber is susceptible to shrinkage, so to prevent this, you may want to use ballast to make your roof more robust. This usually costs around £2 for a large bag and up to £40 for a bulk bag.

Those with a fibreglass roof can prevent replacement or repairs by regularly applying acrylic paint to their roof covering. This will not only make it look brand new but will also protect the insulation and prevent a build of internal moisture – acrylic paint costs around £9 to £170 per tin.

Cost of Removing a Flat Roof

If you want to convert your roof, you will need to have your flat roof completely removed. It may be that you have no choice due to consistent leaking or rotted timber decking, which will require you to remove your roof. The average cost for professional removal is around £80 per square metre, although this will depend on the material used, as some may be harder to remove than others.

You will also need to consider waste disposal costs which usually amount to £100 if a tradesman is removing it for you, if you need to hire a skip expect to pay around £200 to £1,000 for skip hire.

FAQs

The cost of a new flat roof will depend on several factors including the specification of roofing materials, height and access, location, size of business carrying out the work, and the actual size of the flat roof area. But the costs for a replacement felt roof using the common bitumen based felt that is applied using a gas-powered blow torch to a flat roof over a double garage, would cost around £1,000 on average.

This figure would include the removal of the existing roof felt, an inspection of existing timber, supply and install of underlay, supply and installation of the cap sheet, supply and installation of all edgings, and the disposal of all waste material from the site. The cost would increase for a flat roof in a habitable part of the building as more insulation would be required, the presence of asbestos in the old roof would also considerably increase costs, as would access or height problems requiring scaffolding.
No, actually cowboy builders do this all the time, leaving the original felt in place and just put the new roof material on top. This can lead to a whole host of problems which will no doubt begin to appear just shortly after the builder has disappeared into the sunset with your money!

Removing the old felt is an essential part of the job as the timbers underneath need to be inspected or replaced. This will last for a year or less until the movement of the roof, UV rays from sunlight, and damaged existing roof cause it to split and leak.
It all depends on size, access, height and type of materials used. But on average a single garage repair and replacement should take one day with two men working, and with a double garage allow for a day and a half. Note that even on small jobs taking less than one day, a competent and professional roofer would always come back the next day to ensure that the flat roof was watertight overnight.

Unusually shaped flat roofs or roofs where there is a lot of cutting around roof windows or pipes required will take longer, as will flat roofs on second or third storeys which will require scaffolding or access towers.
All flat roofs should be inspected twice a year in Spring and Winter, ideally just after some rain or snow so you can check the water on the roof is draining away correctly and not pooling. Note that before you attempt any flat roof inspection, you must take suitable safety precautions, unless 100% unsure of the condition of the roof do not step onto the roof, or if you must then use a sheet of plywood to distribute your weight evenly across a large surface area.
The main features of a flat roof include a low slop of between ¼ to ½ inch which allows it to drain water. However, unlike other sloped roof types, it can hold water for a limited amount of time. There are three main types of flat roofing including built-up roofing which features layers of felt and gravel, Modified Bitumen Roofing which is made up of asphalt-based material and membrane roofing which usually features EPDM rubber and plastic.
A professionally sealed flat roof should last 20 years or more without leaking, so the worst-case scenario for most of us would be having to replace it 3-4 times at most, with the total cost still being much less than building a pitched roof (on average you could completely replace a flat roof around 15 times to spend as much as one single pitched roof build).
There are several options to choose from, including traditional materials like felt which has a good lifespan and is easy to repair. Other alternatives include EPDM rubber, a highly water-resistant roofing material, which has less to worry about regarding leaks. Fibreglass is also a popular choice due to the great aesthetic it offers, and it is also easy to repair.
Yes, the majority of flat roofs can be repaired easily by a professional or by yourself, as long as the damage is minor, as on some occasions you may have to replace the roof entirely. However, for holes, small leaks, flashing damage and blisters all that needs to be done, is remove debris and clean the affected area and apply new material.

How to Find & Hire a Flat Roof Specialist

The average roofer rate is around £18 to £25 per hour. The price will depend on the type of job, as well as the experience of the tradesmen. To ensure that you are hiring a reliable worker, you should check they have more than 5 years’ experience roofing, while also making sure that they have public liability insurance to protect them and you in the event of an accident. You may also want to check if they have a diploma in roof slating and tiling. However, this is not a legal requirement to become a skilled roofer.

Sources

https://www.doityourself.com/stry/how-to-remove-a-rubber-roof-membrane
https://www.wikihow.com/Replace-a-Flat-Roof
https://www.fixmyroof.co.uk/videos-and-guides/flat-roof-replacement/flat-roof-costs/
https://www.fibreglassdirect.co.uk/blog/post/roof-repair
https://gooforit.co.uk/product/roof-gutter-hole-repair-kit/
https://www.gee-grpfibreglassing.co.uk/cleaning-maintenance-of-a-grp-roof/
https://www.roof-stores.co.uk/guides/flat-roofing/maintain-flat-roof/
https://www.dctaylorco.com/blog/shrinkage/
https://science.howstuffworks.com/environmental/green-science/green-rooftop.htm

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