A Look at Replacement Flat Roof Prices [Updated May 2020]

Flat roofs are more likely to leak than any other type of roof covering. Let us guide you through the three most popular flat roof replacement options and of course, how much each will cost.


(Not sure which type of flat roof covering is best? Don’t know your fibreglass from your EPDM rubber or your torchon felt? Check out this guide where we explain the pros and cons of each option)

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Unbiased and Sound Advice From a Flat Roofing Contractor With Over 20 Years Experience

Check out this advice from an experienced roofing contractor:

Flat roofs are not supposed to be built perfectly flat, as bizarre as that may sound. The best thing you can do to ensure the finished flat roof will last as long as possible is to make sure any rainwater discharges off the roof and into the outlets or gutters without pooling on the surface. Any ponding of water will lead to a build-up of algae, sediment and mosses that can affect the surface materials, potentially shortening the life expectancy of the flat roof covering.

Here are three common reasons why water may pool on a flat roof and what you need to do to fix each:

  1. The decking (usually ply but historically chipboard) has sagged between the joists and the felt covering has sunk too, water now pools in puddles. Solution: Replace the decking boards with OSB boards and install a new felt covering.
  2. Rainwater flows the wrong way on the roof and pools. Solution: The decking should be raised at one end with firings (see image here) so the roof is higher at one end and lower at the other end where the guttering or water outlet is located. This work should be completed before the installation of new felt coverings.
  3. Flat roof has an internal water outlet that blocks frequently. Solution: Ask a flat roof company to widen the outlet hole if possible and install a leaf guard (like this product) to prevent blockages.

Not sure if your flat needs a complete replacement or can be repaired? Try our flat roof repair troubleshooting guide (with lots of photos and examples).

Flat Roof Pricing Examples

Below you will find three price examples for both single and double garage roofs, these are the most common types of flat roofs in the UK, so use these figures as a starting point:

1) Built-up (Torchon) Felt System

This type of flat roofing felt has been in use for decades and is still used today.

Layers of bitumen felt are heat-welded onto each other to form an impenetrable barrier.

Here is a video showing how the felt is installed on the flat roof:


Price guide:

Project:Price:
Single garage£1200.00 inc vat
Double garage£2000.00 inc vat
Get a Custom Price HereGet a Custom Price Here

Materials Required to Replace a Typical Single Garage Flat Roof

Here we delve into the cost of the materials for a typical single garage flat roof.

We have also provided suggested costs for waste removal, labour costs, profit margins and VAT:

  • New OSB decking boards (optional) – £50.00 each supply and fit inc VAT
  • Firrings £50.00  (optional) inc VAT
  • Base layer £40.00 inc VAT
  • Mid layer £80.00 inc VAT
  • Top layer a capsheet with a mineral finish £200.00 inc VAT
  • Waste disposal – £100.00 inc VAT
  • Labour for two people – £180.00
  • Building control notification – £50.00
  • Net profit – £200.00
  • VAT on labour and profits – £76.00

Assuming you only need the felt replacing with a 2-layer system (often used on garages and sheds) – £775 inc VAT.

For a 3-layer felt only system (required over habitable and insulated areas of the house) – £850.00 inc VAT.

For a complete replacement including new decking boards with a 3 layer system – £1200.00. Add £50 for firrings if needed.

We haven’t included the cost for replacement guttering, fascias or soffits. Also, additional insulation may be needed on some flat roofs to meet current regulations.

Don’t forget; our breakdown of the flat roof costs are for a single garage roof.

What About a Double Garage?

The price breakdown shown above is for a single garage.

A double garage with a 3-layer system and new decking usually costs around £2000.00 inc VAT.

Update 2020: Try our flat roof cost calculator (no email or signup required).

2) Rubber EPDM System Roof Cost

There are several different types of EPDM material and as with any other type of felt, the weak point is the joints.

That’s why we prefer the one-piece rubber membrane as it doesn’t have any joints and in our opinion is less likely to leak in the future.

(Update May 2020: EPDM rubber roofing materials have come a long way in recent years and if installed correctly, joint separation should not be an issue.)

Below is a nifty video guide explaining how a one-piece membrane is installed:

Below is our suggest cost guide for rubber flat roofs:

Project:Price:
Single garage£1050.00
Get a Custom Price HereGet a Custom Price Here

Here is the approximate cost of the materials for a single roof:

Rubber membrane – £220.00 +vat

Adhesive and sealant – £50.00 +vat

Edgings and drip edge – £140.00 +vat

Waste disposal, decking, fascias, guttering, building control notification etc as extras if needed.

Update May 2020: We’ve recently updated our popular EPDM flat roof cost calculator. Instantly get a price online. Enter your roof’s dimensions and answer a few basic questions, we won’t ask for your email or any personal information.

3) Fibreglass Flat Roof Covering Prices

Fibreglass is a long-lasting, tough, yet slippery material that has been used as a flat roof covering for decades.

It’s commonly seen on smaller flat roofs such as single garages, porch roofs and door canopies.

There is a downside to fibreglass – unlike bitumen felt, it cannot be laid onto old ply or chipboard. New OSB boards must be laid down first, this can make fibreglass expensive for larger roofs.

Below is a video showing how fibreglass is secured to a typical flat roof:

Price guide:

Project:Price:
Single garage roof inc decking boards:£1500.00
Get a Custom Price HereGet a Custom Price Here

Material cost – below you’ll find a list of the materials required to replace a single garage flat roof, along with prices:

Resin and catalyst – £200.00 +vat

Tissue – £30.00 +vat

Topcoats – £130.00 +vat

Trims and baton – £100 +vat

OSB boards – £45.00 + vat each supply and fitted

See The Prices Our Site’s Visitors Have Been Given For a New Flat Roof:

We think these prices are really insightful.

Have you been given a price from a flat roofing contractor?

Let other visitors know how much it cost by filling out the contact form (no email or personal information required).

Name:Desc:Price:
Pam and Jim Peters (SL4 2SG)Roof on annexe size 20’x10’. 3 layer felt 100mm thick. (2020)£1170 +VAT
Vicky (Oxford)Single garage roof, replacement of boards and roofing felt including lead flashing. (2020)£1750
Lee (Gainsborough)To give you an idea of materials cost (so you can work out what your contractor is charging for labour) I have just completely replaced my large 3m x 12m garage/extension roof. I replaced everything from the firrings upwards (so firrings, deck, epdm 1.5mm, all trims, new fasica and completely new guttering. The materials cost came in about £1600. My area is about twice the size of a standard domestic garage. (2019)£1600 (materials only)
Rachel Effie (Sunderland)3x2. Bathroom flat roof 1 board to be replaced and flat roof (2019)£450
Dave James (Darlington)Bay window approx 2m x 0.75 m
fibreglass (2019)
£450
E Davies (Essex)7M x 4.5m dorma flat roof replace old felt with high tech (Protan) Membrane. 20 years (Life time guarantee while we live here) insurance backed. Price does not include decking or insulation. (2019)£6335
Susan Walker-Mitchell (Royston nr Cambridge)I have a single garage currently covered in felt. I've received 3 quotations for replacement with a torch on system. One was £2,500 (rejected straight away as being ridiculous), another was over £17,500 and another was £14,050. They all seem very very high for a relatively small area. I haven't yet made a decision though the company that gave the lowest quote keep ringing and emailing to get me to say yes. (2018)See notes
Martin (London)Flat roof 4.5m x 3.6 m
Replace old bitumen with GRP Pro fibreglass, add new decking on top, plus one low parapet wall at edge with reclaimed London bricks (2018)
£8000
Paul Johnson (Birmingham)2nd storey loft extension, flat roof Firestone rubber EPDM 6.5m x 3.5m (2018)£3750
Ian Jones (North Wales)Single garage fibreglass flat roof (2018)£1500
C. Norton (Lancashire)Flat roof 3 metres X 5 metres. EPDM rubber, asked for extra fall on roof to be made. New flashing. New plastic facia boards and guttering. (2018)£2150
Maria (London)The flat roof is torch on Bitumen with torch on flashing, this roof has been patched repaired previously, torch on felt roofs have an approximate life span of 10-12 years merely as a covering. We would recommend a different covering such as GRP fibre glass.
To supply & fit GRP (fibre glass) complete with a 20 years manufactures warranty, flat roof complete with 18mm OSB tongue & groove boarding laid on top of firming pieces to correct slopes – (not suitable as a balcony)
(size is approx 3m x 3m) (2018)
£4850
Lisa (Derby)10x3 meter dorma with epdm and insulation below - include removal of old felt (2017)£2750

Which Material is the Best?

Now you have a good idea of how much a new flat roof will cost, you’ll need to decide which material is best for your roof.

There are pros and cons to each material, so we’ve created an in-depth guide that is targeted to beginners and those with very little knowledge of flat roof options.

Explore our impartial guide and discover answers to questions such as:

  • Do I really need to replace the costly timber decking underneath the roof covering?
  • Which option is best?
  • Which material is cheapest?
  • Which will last the longest?
  • What type of flat roof looks the most appealing?
  • Do I need extra insulation?

Check out our impartial guide to flat roof options here

Asbestos Flat Roofs – Does Your Roof Contain Nasty Asbestos?

We recently got in touch with several asbestos removal companies and asked them how much it costs to safely remove asbestos sheets from a flat roof.

The cost was much less than we thought, explore our guide to asbestos removal costs here.

Asbestos was widely used in the 1970s and ’80s, even into the ’90s.

Not sure what this harmful material looks like?

Here’s a photo:

Just to confuse matters, there are several products on the market that look identical to Asbestos but in fact, don’t contain any of this dangerous material.

These were created for repairs and replacements of damaged asbestos:

Asbestos is quite safe provided it isn’t disturbed. If you have an asbestos flat roof and you want to replace it with fibreglass, felt or rubber, first check our guide to asbestos roof removal costs.

Insulation – Do You Need it to Comply With Building Regulations?

Just when we thought we’d covered all aspects of flat roof prices, along comes another consideration.

Since 2005, if you replace 25% or more of your roof covering (felt) then you need to ensure that the entire flat roof has enough insulation to satisfy current building regulations.

This only applies to flat roofs over habitable parts of your home, so it excludes garages, sheds some porches and most door canopies.

How much insulation you’ll need depends on how much is already in your roof.

Visit our impartial guide to flat roofs for more information.

Can a Flat Roof be Repaired? How Much Does a Typical Repair Cost?

Patch repairs are often possible if the flat roof is damaged due to an impact, perhaps a slipped slate, tile or tree branch etc.

However, if the roof has a leak due to its age then patch repairs are often a waste of money, you could also make the leak worse by walking on it.

It’s impossible to predict the cost of a patch repair without first inspecting the roof. Smaller jobs are notoriously difficult to estimate without looking at the roof in more detail.

We would suggest a price of between £100 and £150 for a small patch repair to a bitumen felted flat roof that has a tear, we assume that the decking or underlying roof structure isn’t damaged.

Where Can You Get a Quote?

We hope you found our detailed guide to flat roof prices insightful.

Do consider that our prices are not a substitute for a fixed written quote that is provided after an inspection of the roof.

Let us help you source a competitive price online for your flat roof project.

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More:

Contrary to the name, a Flat Roof isn't always flat. The term is used to describe any roof with a low pitch that requires a covering rather than overlapping tiles. Flat Roofs are often found above garages, dormers and some home extensions.
A single garage roof without decking will take about 4 hours. Removing and replacing the decking and you can expect the work to take around 7 or 8 hours. A double garage flat roof will take a day if you only replace the felt, but with the decking too, allow a day and a half.

The built up system should have 3 layers but on sheds and detached garages many roofers will offer the option of two layers.

Rubber roof membranes require only one layer.

The epdm "one piece" membrane is fairly easy to install but would still be best suited to someone with good carpentry skills.

Torched on felt and fibreglass should be left to experienced contractors.

Building control will need to be notified before and after the project if you intend to replace 50% or more of a roof.

The cheapest way to accomplish this is to employ a roofer that is a member of the "Competent Roofer" scheme.

Members pay a joining fee of around £500 and a yearly renewal of £500. This allows them to self certify their work at a cost of around £50 per project.

When replacing a felt roof, the void between the felt and the ceiling will need to be checked for insulation. If there isn't any or it's not enough to meet regulations, extra insulation will need to be installed. There are various options available but the most popular is a foam-like board sandwiched between the decking and roof rafters.
If the roof needs to be repaired or replaced due to an unforeseeable event such as a healthy tree falling onto it, then yes, you may be able to claim on a home insurance policy. Claims due to wear and tear, age or lack of maintenance are unlikely to be successful.
EPDM rubber is by far the best material for most flat roofs. It's easy to install, affordable and lasts for decades.

This guide was written by and was last updated in May 2020.

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Author - Danny Woodley