Roof area
Everything is priced per square metre, so area is the starting point. Measure the roof rather than the room below it, and remember that upstands, parapets and kerbs add area that is not visible on a floor plan.
Price guide · Updated 2026
What Does a Flat Roof Cost in London?
Indicative market rates for repair, overlay and replacement, what actually moves the price, and how to read a quote. Figures are UK market rates for 2026, not our prices.
Get a free surveyWhat a flat roof costs, and why the answer is a range
A flat roof in London costs somewhere between roughly £40 and £180 per square metre depending on the system, plus 25 to 30 percent for London labour rates, which means a typical extension roof lands anywhere between about £1,300 and £5,000. That range is wide because it is doing a lot of work: it covers everything from a felt roof on a garage to a certified liquid system on an occupied commercial block.
This guide breaks the number down so you can tell where your own roof sits, and so you can compare two quotes that differ by thousands and understand why. Every figure here is an indicative UK market rate for 2026 taken from published trade sources. None of them is a quote from K & M Roofing Solutions, and no honest contractor will give you a firm price for a flat roof without seeing it first.
What costs what
Cost by flat roof system
Per square metre, before the London uplift of 25 to 30 percent.
| System | Rate per m2 | Typical service life | Notes |
|---|---|---|---|
| Three-layer felt | £40 to £80 | Commonly 15 to 20 years | The building regulations standard over habitable rooms. Cheapest to install, shortest life. |
| EPDM rubber | £80 to £120 | Longer where detailing is right | A single rubber sheet, light and flexible. Good on simple shapes, joints limited to edges and penetrations. |
| GRP fibreglass | £100 to £150 | Can last decades | Hard, seamless and walkable. Needs a clean dry deck and mild weather to install. |
| Liquid applied | £40 to £180 | See the note below | The widest published range on the market, and the one that needs explaining rather than quoting flat. |
Indicative UK market rates for 2026, not prices from K & M Roofing Solutions. Add 25 to 30 percent for London and the South East. Service life figures are material-specific and depend heavily on the deck and the detailing, not on the headline product.
What moves the number
Six things that change the price
The material is rarely the reason two quotes differ. These are.
Condition of the deck
A sound, dry deck is the cheapest outcome available to you. Rotten boarding, saturated insulation or a deflected deck means strip-out, disposal and replacement, and that is what turns a modest overlay into a full replacement.
Access
A garage roof reached from a ladder and a third-floor parapet roof over a shop are different jobs at the same square metre rate. Scaffolding, towers, pavement licences and craneage are separate lines and should be itemised as such.
Details and penetrations
The flat field of a roof is the easy part. Outlets, upstands, pipe penetrations, rooflights, parapet abutments and door thresholds are where the labour goes and where roofs actually leak.
Insulation and Part L
If more than half the roof covering is being replaced, Building Regulations Part L generally requires the insulation to be upgraded to current standards. That is a real cost, it is not optional, and a quote that ignores it is not comparable with one that includes it.
Waste and disposal
Strip-off means a skip, disposal charges and labour to fill it. Older bitumen sheeting may contain asbestos, and licensed removal runs £55 to £95 per square metre on its own. An overlay removes this entire line from the quote.
Repair or replace: the comparison that matters
Refurbishing a sound flat roof costs markedly less than stripping and replacing it, and the reason is arithmetic rather than salesmanship. A replacement carries four cost lines that an overlay does not: the labour to strip the existing covering, skip hire, disposal charges, and the insulation upgrade that Part L generally triggers once more than half the covering comes off. On an older roof you may also be paying £55 to £95 per square metre for licensed asbestos removal.
An overlay removes all of those. You are paying for preparation, priming, detailing and the waterproofing itself, and the existing covering stays where it is. That is why a liquid refurbishment on a sound deck is normally the cheapest route to a watertight roof, and why it is worth establishing whether your deck qualifies before accepting a replacement quote. The saving is largest on a building that cannot close, because a strip-out means shutting the space underneath it, which is set out on our page for commercial flat roofing in London. Whichever route the roof needs, the work carries a 10-year workmanship guarantee and is rated 5.0 from 60 reviews on Google.
The honest limit is this: an overlay only works if the deck is structurally sound and the insulation underneath is dry. If the boarding has rotted, the insulation is saturated or the falls are wrong, sealing over the top buries a problem that will resurface. Anyone who tells you otherwise is selling you the cheaper job rather than the right one. Read how liquid applied waterproofing works and when it is not suitable, or see our flat roof repair and waterproofing service.
Reading a quote
Warning signs in a flat roof quote
- A price given over the phone or from photographs, without anyone seeing the roof
- No named product or system, just wording such as membrane refresh or roof restoration
- A liquid system quoted under £18 per square metre on a roof more than ten years old
- A contractor who cannot show applicator certification from the manufacturer for the system quoted
- No mention of insulation on a job replacing more than half the roof covering
- Scaffolding or access buried in the labour rate rather than itemised
- A guarantee described verbally but not issued in writing
- A deposit demanded up front rather than payments staged against completed work
Knowledge
Read more before you decide
Common questions
Flat roof cost questions
As indicative UK market rates for 2026, three-layer felt runs roughly £40 to £80 per square metre, EPDM £80 to £120 and GRP £100 to £150, and London labour typically adds 25 to 30 percent on top of national figures. So a 25 square metre extension roof in London sits very roughly between £1,300 and £4,900 depending on the system and the state of the deck underneath. Those are market figures rather than a quote from anyone, and a binding price follows a survey.
Substantially, when the deck is sound. A liquid overlay costs less than a full replacement because three separate cost lines disappear: the labour to strip the old covering, the skip, and the disposal charges. You also avoid the risk premium a contractor prices in for opening up a roof and finding rot underneath. The catch is that an overlay is only honest if the deck is dry and structurally sound, which is exactly what a survey establishes.
Labour rates in London and the South East run roughly 25 to 30 percent above the national average, and that is the largest part of it. Access adds more: terraced streets mean pavement licences, restricted parking, longer material handling and scaffolding where a suburban house would need a tower. Waste disposal costs more, and working hours are often constrained by neighbours and by the building being occupied.
Because published ranges lump two different things together. At the bottom of the £40 to £180 per square metre range sit single-component acrylic coatings, which are essentially a thick paint with a short service life. At the top sit certified, reinforced systems with a European Technical Assessment behind them, applied by manufacturer-approved installers. Those are not the same product and should not be compared on price alone. If a quote does not name the system and give you a certification number, you cannot tell which one you are being sold.
A named system rather than a generic description, the area in square metres, the preparation work, how the details and upstands will be treated, whether insulation is being upgraded, access and scaffolding as separate lines, waste disposal, and the guarantee in writing with its term and what it covers. If two quotes differ by thousands, the difference is almost always in insulation, access or the amount of preparation, not in the roofing material itself.
Usually, yes, if more than half of the covering is being replaced. Building Regulations Part L treats a thermal element renewed to that extent as work requiring the insulation to be brought up to current standards. It is a genuine cost that some quotes leave out to look cheaper. An overlay onto a sound roof typically does not trigger it, which is another reason refurbishment can work out considerably cheaper than replacement.
A localised repair such as resealing an outlet, dressing a blistered lap or patching a split upstand is usually a few hundred pounds, because it is a short visit and very little material. The judgement call is whether a patch is worth doing at all: on a covering that is generally sound it is good value, and on one that is failing across the whole roof it is money spent twice. A survey should tell you which situation you are in rather than selling you the patch either way.
Yes, significantly, and it is common in older bitumen sheeting and some older felts. Licensed removal and disposal runs roughly £55 to £95 per square metre on its own, on top of the roofing. This is one of the strongest arguments for an overlay where one is possible, because sealing over a sound asbestos-containing layer and leaving it undisturbed avoids the removal cost entirely. It has to be identified before work starts, not discovered halfway through.
It depends far more on the detailing and the deck than on the headline material. Three-layer felt commonly reaches 15 to 20 years, and EPDM and GRP often go longer where the deck is sound and the upstands and outlets were done properly. Keeping the outlets clear is the single cheapest thing an owner can do to extend any flat roof. K & M Roofing Solutions issues a 10-year workmanship guarantee and does not make durability claims beyond that for the work it carries out.
They are indicative UK market rates for 2026, gathered from published trade sources, and they are not a quote from K & M Roofing Solutions. They are here so you can sanity-check whatever quotes you are holding and understand what drives the difference between them. Any price we give you follows a free survey of your actual roof, and it is itemised so you can see what each element costs.
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The figures above are market rates. The only way to price your roof is to look at it, which we do for free and without obligation.
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