How Much Does a New Flat Roof Cost?

Is your flat roof leaking and does it need to be replaced with a new covering? Due to the way flat roofs are constructed, water often pools on the surface, this is fine until the felt fails, then the water enters the home and causes damage.

Water damage from a leaky flat roof can range from a minor damp patch on the ceiling to severe rot and failed timbers.

Act quickly, get your roof covering repaired or replaced quickly and you’ll limit the amount of damage.

Leave it too long and you may need to replace costly timber decking and roof rafters as well.

Our Price Guide

If you’re looking for a price guide for replacing a flat roof then you’ve come to the right place.

The folks behind Quotation Check sent out price requests to dozens of roofing firms in 2016 and again in early 2018.

Below you’ll find the results of our research which we last updated on the .

Use our guide to get a handle on prices and steer clear of companies that overcharge.

We can also help you get a competitive written quote.

Flat roof on garage

Price Variations and Nuances

Your flat roof is constructed from several different parts:

  • a top layer of felt, rubber or fibreglass
  • timber decking to support the top layer
  • timber joists
  • insulation to keep you warm (now mandatory as per the regulations)

How much it costs to replace a flat roof will depend on how many elements of the roof need replacing.

Hence why it’s so important to fix any issues before they escalate and damage the timbers under the roof.

Is it just the felt top layer that’s damaged?

Is the decking in good condition or has it failed?

Does the flat roof already contain insulation and does it meet current building regulations?

Other things to consider are:

  • if scaffolding is required to gain access to the roof (see our scaffold price guide here)
  • the quality of the materials
  • the size of the roof
  • how high up the roof is located

Example Quote 1 – Double Garage Flat Roof

Below is a typical works schedule for the replacement of a flat roof above a double garage.

The price displayed is an average of the figures we received from dozens of roofing firms in the UK.

Work Schedule:

Here is a list of all the work involved with replacing a typical double garage flat roof.

  • Protect the contents of the garage by covering the items with a tarpaulin
  • Remove any stones from existing roof and tear up the existing felt covering
  • Survey the existing timbers and replace any decking as required (priced separately per sheet)
  • Supply and install one layer of underlay tacked to the decking
  • Supply and install one mid layer of felt
  • Supply and install one cap sheet with a coloured mineral finish on the surface
  • Supply and install all edgings including wall upstands and drip edges which overhang into the gutter
  • Quote includes timber fillets and timber batten as required
  • Remove and dispose of all waste material
LocationSmall Business /TraderLarge Business
London Area£1050.00£1300.00
South, SW and Midlands£1050.00£1250.00
Outer Region and North£900.00£1000.00
Need a Custom Price? >Compare Up To 3 Personlised Quotes Here

Price Example 2 – Extension Roof

Cost to replace felted flat roof covering

Typical Flat Roof

In our second cost example, we have an extension roof at the rear of the property that requires some additional work:

  • insulation
  • scaffold
  • new lead

Works Schedule:

  • Erect scaffold tower up to the desired work height
  • Remove any stone chippings from existing roof and rip up existing felt covering
  • Replace existing timber decking that’s failed
  • Supply and install one underlay, tacked to  the decking sheets
  • Supply and install one mid-layer
  • Supply and install one cap sheet with a mineral finish on surface
  • Supply and install all edgings including upstands and drip edges which overhang into the gutter
  • Quote includes timber fillets and timber batten as required
  • Quote includes lead dressed onto felt to prevent water ingress (see photo 2)
  • Supply and install insulation placed between roof rafters underneath the new decking
  • Remove and dispose of all waste material
LocationSmall Business /TraderLarge Business
London Area£1450.00£1950.00
South, SW and Midlands£1100.00£1500.00
Outer Region and North£975.00£1200.00
Need a Custom Price? >Compare Up To 3 Personlised Quotes Here

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Extra Costs to Consider

Lead Overhanging Onto Flat Roof

Lead Overhanging Onto Flat Roof

The folks behind Quotation Check prefer fixed written quotations to estimates.

With a detailed written quote, the consumer knows exactly how much the work will cost and precisely what work is being done.

Estimates are much vaguer and leave far too much wriggle room for unscrupulous traders, hence why we don’t like them.

Unfortunately, flat roofs can be difficult to quote for as it’s often impossible to inspect the timber until the roof is stripped off

Our Suggestions

We suggest you only accept a fixed written quotation. If your roofing contractor is unable to visually check the timber, they can give you a separate price for repairing or replacing it, if it’s needed.

Decking boards aren’t cheap and cost between £45 – £60 each delivered and fitted. A typical garage roof contains up to six decking boards.

Decking boards that have dipped, become rotten or are made from weak chipboard should be replaced.

Other Possible Costs

Change the slope of the roof – You would think that a flat roof is “flat” – right?  Well, they are not, a “flat roof “should have a slight slope, so rainwater runs off the felt and into the gutter. If the roof was perfectly flat, then water would “pond” on top of the felt, this could shorten the life expectancy of the felt and isn’t ideal. Your contractor can fit additional timbers to raise one end of the roof by a couple of inches. This will obviously cost more and isn’t included in our price examples on this page.

Stones and chippings – Do you need to have shingle/chippings placed on the top of the felt? Stones/chippings were used decades ago as a way to protect the felt from sunlight which would shorten the life expectancy of the felt by drying it out and causing cracks.  In the price examples above, we have specified a”mineral finish” felt, this type of cap sheet already has chippings bedded into the felt, so you do not need to lay stones on the roof. That would be an optional extra. Some homeowners don’t like the appearance of felt, so hiding it under a layer of stones is certainly possible.

Extra insulation – If your flat roof is located above a habitable part of your home then the building regulation state that you must have adequate insulation between the roof and the room below. How much you’ll need depends on how much is already there. The good news is that insulation isn’t expensive and you’ll save money on your future heating bills too.

Can Old Flat Roofs be Repaired and is it Worth the Cost?

If your existing flat roof is leaking, then it may be possible to repair it rather than replacing it.

The most common areas where leaks occur are:

  • Where the felt joins a wall, this is called an upstand
  • The drip edge – where the felt overhangs into the gutter
  • Damage caused by falling tiles or other third-party damage

If your roof is leaking due to any of these examples, then a patch repair may be possible, this will obviously cost considerably less than a full replacement.

If however, your roof is leaking because it’s old, has suffered from cracks /UV damage or has a significant amount of water pooling on it etc then doing a patch repair is not a realistic long-term solution.

Cutting Corners – Watch Out for This

One method some unscrupulous roofers use is to leave the original felt in place and just put the new materials on top of it.

While there are occasions when this technique is acceptable, any defects in the original flat roof can transfer to the new covering.

We recommend that your installer first removes the old felt, so he/she can inspect the timbers underneath and make good any necessary repairs.

Another con is when the roofers cover the roof with a liquid tar or sealant, these are usually good for a year or two until the movement of the roof and UV rays cause it to split and leak, so we don’t recommend these as a long-term solution.

How Long Does it Take to Replace a Flat Roof?

For a single garage, the work can easily be completed in one day if two men were working on the project. Even if additional timber work was required it is unlikely that the project would take more than this

For a double garage or a similar sized flat roof, the work could extend into a second day, although the roofer will make sure that the flat roof is watertight overnight.

Unusually shaped flat roofs or where there is a lot of cutting required (around pipes, Velux windows and parapet walls, etc.require) will need extra time and this will be reflected in the cost.

6 Questions You Should Ask Your Roofer

The flat roofing industry has a bad reputation in the UK, so here are a few questions you should ask, we suggest you get the answers in writing:

  1. Will you remove the old felt or cap over it?
  2. Will you make sure the water doesn’t pond/pool on the new felt? Will this cost more? How much?
  3. How much will any new decking cost per sheet? And how many sheets are on the roof?
  4. If the felt is butted up against a wall, will he use costly lead or cheap felt as an “upstand” ?
  5. What is the finish of the felt? Stone chippings or mineral felt finish?
  6. Does the roof need insulation to meet the building regulations (not needed for garages) and how much will that cost?

Other Materials to Consider

Torch-on bitumen mineral felts are an extremely popular choice for roof coverings and if applied correctly will last 15+ years.

They’ve also been around for decades, so are a tried and tested method

That’s why we recommend them and have included them in the price examples on this page.

Other materials to consider are:

  • Mastic asphalt which is a tar-like substance layered onto the roof by hand in one seamless piece. It’s costly, very few people are qualified to complete this work but it lasts for many years, certainly longer than 20.
  • Rubber based membranes such EPDM are another material you could consider.
  • Fibreglass is a hard and long-lasting material, provided the substructure is solid and won’t flex.

How Trustworthy are Roofers in the UK?

Trustworthy Tradespeople UKWhen we launched our site in 2014,  we wanted to know how tradespeople were perceived in the UK.

That’s why we created our poll.

To date, over eight thousand people have taken part.

See the results and cast your vote. Are roofing contractors seen as trustworthy in the UK?


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12 Responses to “How Much Does a New Flat Roof Cost?”

  1. Jamie LairdOctober 22, 2015 at 6:14 pm #

    Flat roof should have loose layer if not boards need primeing and for double garage your cheap couldnt do it for that

  2. alan obMay 24, 2016 at 2:08 pm #

    Don’t know when you put those numbers together but today they seem to be nearly twice what you suggest above for a double garage roof in the south east. Three quotes all small business around the 2k mark for 3 layer felt and new OSB deck

    • QuotationCheck AdminMay 24, 2016 at 2:53 pm #

      We created this page back in November 2014. The figures shown for the double garage flat roof do not include the cost of OSB board replacement which costs between £40-55 per sheet to supply and fit. Also we asked for a two layer system rather than a three layers, which would cost more. So for full board replacement and three layers I feel £2k isn’t too far off.

  3. MartinJune 19, 2016 at 3:01 pm #

    Part L no mention of cost to consumers or do most felt roofers just forget to inform there customers
    They should be informing building control at an extra cost
    Now who is the cowboys ?
    And surely a 3 layer system should be standard ?

    • GeorgeSeptember 16, 2016 at 7:18 am #

      PL is only triggered if more than 50% is to be replaced. I agree, no less than 3 layers should ever be used.

  4. AlexDecember 11, 2016 at 2:59 pm #

    This is a very informative article, even an industry person find it very detailed and honest, because usually contractors will not list out pricing publicly and loses the chance to close a sale without an initial approach with clients. Wish you all the best with your business.

  5. MartinMarch 19, 2017 at 10:34 pm #

    Hi. You mentioned that one of the biggest bodge jobs is laying straight over exciting felt…….so is, (let’s say) the Evolution one layer system with a 12-15 year guarantee a bodge?? Nearly £100 a roll, and saving maybe hundreds of pounds in labour and skip hire… this still a bodge if applied correctly??

    • PaulMarch 26, 2017 at 11:16 am #

      It is as the weight of the existing felt added to new may exceed the design if it has some on it. No point in saying it doesn’t snow much, it only needs to do so once.

  6. DanAugust 13, 2017 at 5:49 pm #

    A builder who quoted me for three layers i.e tacked underlay, midlayer and top layer with mineral finish ended up actually just putting underlay (torched) and top layer with mineral finish. On seeing this got annoyed so he agreed to put an additional top mineral layer.

    Will this be problematic for me in the long run?

  7. John ElliottOctober 23, 2017 at 8:35 pm #

    You need to update your prices to this century.

  8. RaeMarch 4, 2018 at 2:11 pm #

    My parents needed the flat roof in their bedroom and Ensuite that was built over the double garage about 35 yrs ago.

    They’ve had no probs till this year but unfortunately I can’t remember the name of the Product / Process they used. I’m pretty sure it’s fairly new and it was I think some kind of rubberised material.

    It was done in really good time and cane with a 50 year warranty! It also turned out a little cheaper than the old standard.

    I don’t know exactly what the roof problem was but rain was pouring through their bedroom ceiling for weeks ! All good now though.

    One of my ground floor rentals needs work on a smaller flat roof soon (allegedly) and the freeholder who gets the work done (he says) then bills us leasehokders with no proof of any costs whatsoever but that’s a separate issue. He is known for using mates, not doing all the work he claims and padding the bills so I want to reconmend this…stuff…to him.m I’d only I dustjacket missing recall the name

    You’d think my folks wld know but they’re not sure what day it is mostly

    Thought it may he be worth a try putting a shout out on here in case this roof treatment rings any bells with anyone? (I do know it’s not bitumen !)


  9. John P NaisbittApril 28, 2019 at 8:09 am #

    I have been quoted £3.4k for a full replacement
    6x3m flat roof
    Joists, OSB deck, fascias, single shutter and down pipe.
    Single layer membrane cover
    Removal of full concrete fibre sheets and old wooden fascias.
    I am trying to get comparisons but companies are reluctant to commit.
    Is this a reasonable quote?

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