Flat roof replacement cost, worked out per square metre
£45 to £120 per m²
A flat roof replacement costs roughly £45 to £120 per square metre fitted, depending on the covering: felt at the bottom, EPDM rubber in the middle, GRP fibreglass at the top. On the roofs people usually ask about that comes to about £750 to £2,400 for a single garage and £600 to £2,160 for a small rear extension, before scaffolding. Scaffolding, where the roof needs it, is £500 to £2,500 on its own and is often the largest line on the quote.
Every published guide gives a different answer to this, and the gap between them is not small. Read five of them today and you are told the average flat roof replacement is £8,000, or £2,800 to £7,500, or about £2,750, or £1,440 to £3,400, or £1,500 to £6,000. That is a factor of nearly six between the highest and the lowest.
They are not disagreeing about the price of roofing. They agree about that almost exactly: every one of them puts the rate somewhere between £45 and £130 per square metre. What they disagree about is how big a flat roof is, and since none of them say which size their average assumes, the number you get depends entirely on which page you landed on.
So this guide works backwards. It takes each published average, divides it by that guide's own published rate, and shows you the roof size the average must be describing. Then it applies the rate to the roofs people actually ring about: a garage, a rear extension, a dormer. You can check every line of it with a calculator.
Show the working
Where the averages actually come from
Start with the one that is internally consistent. Rubber Roofing Direct publishes £1,440 to £3,400 for a flat roof and £45 to £100 per square metre. Divide the low by the low and the high by the high and you get 32 square metres both times. Their average is a 32 square metre roof, and they have simply not said so.
Now the outlier. The Federation of Master Builders publishes an average of £8,000. At the £75 to £120 per square metre that the other guides on the same results page quote, £8,000 is a roof of 67 to 107 square metres. That is not a garage and it is not a rear extension. It is a full-width flat roof over most of a house, or a commercial one.
MyJobQuote sits at the other end with about £2,750 for London. At the same rates that is 23 to 37 square metres, which is a large garage or a decent extension. Checkatrade's £2,800 to £7,500 spans from roughly 37 to 100 square metres. Knights Roofing's £1,500 to £6,000, against their own £40 to £130, is about 37 to 46.
Line those up and the picture is clear: the rate is settled and the roof size is not. So the useful question is never "what does a flat roof cost", it is "how many square metres is mine, and what is going on it". Measure the roof, pick the row below, and the arithmetic is yours rather than an average of somebody else's houses.
One thing to hold on to while you do it. A flat roof is measured as the actual area of the deck plus the upstands, not the floor area of the room underneath, and small roofs carry a minimum: nobody sets up, strips and re-covers a four square metre porch for four square metres of money. Below about eight square metres, expect a day rate rather than a rate per metre.
Three coverings
What each material costs and how long it lasts
The rate is the fitted rate, covering the material, the labour and the trims. Which one suits your roof is decided by how much detail is on it rather than by budget alone.
- Torch-on felt£50 to £80 per m²10 to 20 years
- The cheapest to buy and to fit, and the covering most of the flat roofs being replaced today are made of. Fine on a garage or a shed. Its weakness is the seams and the fact it goes brittle, which is why the failures are always at an edge.
- EPDM rubber£80 to £100 per m²20 to 30 years
- One sheet across the whole roof with no joins in the field, which is why it suits big plain areas like a garage or a full-width extension. Less happy on a roof full of upstands, pipes and awkward corners, because every one of those is a bonded detail.
- GRP fibreglass£95 to £120 per m²20 to 30 years
- Laid wet and cured hard, so it takes any shape and forms its own trims. That makes it the one for dormers and anything with a lot of detail. It has to go on dry and reasonably warm, so a wet fortnight in January delays it.
Find your roof
What a flat roof replacement costs by size
Every figure below is the rate above multiplied by the area on that row, low against low and high against high. Nothing here is an average of anybody else's houses, so you can check it. Scaffolding and waste sit outside these numbers and are listed underneath.
| Roof | Area | Felt | EPDM rubber | GRP fibreglass |
|---|---|---|---|---|
| Porch or bay roof | 4 to 8 m² | £200 to £640 | £320 to £800 | £380 to £960 |
| Dormer top and cheeks | 6 to 10 m² | £300 to £800 | £480 to £1,000 | £570 to £1,200 |
| Small rear extension | 12 to 18 m² | £600 to £1,440 | £960 to £1,800 | £1,140 to £2,160 |
| Single garage | 15 to 20 m² | £750 to £1,600 | £1,200 to £2,000 | £1,425 to £2,400 |
| Full-width rear extension | 25 to 40 m² | £1,250 to £3,200 | £2,000 to £4,000 | £2,375 to £4,800 |
| Double garage | 30 to 36 m² | £1,500 to £2,880 | £2,400 to £3,600 | £2,850 to £4,320 |
Before you compare two quotes
The lines that sit outside the rate
- Scaffolding or a tower, £500 to £2,500 depending on height and how much of the elevation has to be covered. A single garage usually needs none of it, which is most of why a garage roof is cheap
- Waste and disposal, £150 to £400 for skipping the old covering and any rotten decking
- New decking, where the boards have gone soft. Nobody can price this honestly until the old covering is off, so what you want in writing is the rate per board rather than a number
- Insulation, if the roof is over a heated room. Bringing a warm deck up to current building regulations adds materials and height, and it is the difference between re-covering and rebuilding
- New trims, drips and outlets, which should be in the quote and are the first thing a cheap one leaves out
- Firrings, if the falls are wrong and water is standing on the existing roof. Correcting a fall is joinery before it is roofing
This is where the gap between a cheap quote and a dear one usually is. Two prices are only comparable when they cover the same list, and most of the difference is scope rather than margin.
Why two quotes differ
What moves the number
- Area, and only then the material
- The rate spread between felt and fibreglass is about two to one. The spread between a porch and a full-width extension is ten to one. Measure first, choose the covering second.
- How much detail is on it
- Upstands, abutments, pipes, roof windows and a junction with the main roof are where the hours go. Two roofs of the same area can be a day apart because one of them is plain and one is not.
- What the deck is like
- A sound deck gets re-covered. A soft one gets re-boarded, and on an old garage that can be the whole roof. This is the single biggest reason a final invoice differs from a quote, so get the rate agreed in advance.
- Access
- A garage roof you can step onto off a ladder and a second-storey dormer behind a locked ginnel are the same square metres and not the same job. Scaffolding is charged for the time it stands, not the time it is worked on.
- Whether it is heated underneath
- A roof over a garage is a covering. A roof over a kitchen is a building element with an insulation requirement, and that is a notifiable job with a different specification.
- Time of year
- GRP needs a dry, reasonably warm day to cure. EPDM and felt are less fussy. In a Yorkshire January that is a real constraint on what can go on and when.
On your street
The flat roofs Leeds actually has, and what they come to
Almost every flat roof I am asked to price in this city is one of three things, and all three sit in the smaller rows of that table rather than anywhere near an £8,000 average.
The first is a rear kitchen extension on a Victorian terrace through Headingley, Hyde Park, Woodhouse, Burley or Kirkstall. Twelve to eighteen square metres, usually the oldest covering on the house because it was added long after the main roof was last touched, and the one that leaks into a room somebody uses every day.
The second is a dormer, which is the Headingley speciality: thirty years of loft conversions in LS6 means an enormous number of them. Six to ten square metres, mostly upstands and cheeks, and a junction with the slate slope that decides whether the whole thing lasts. This is the case where fibreglass earns its higher rate, because a covering that forms its own trims beats one that relies on them.
The third is a garage on an interwar semi out through Weetwood, Far Headingley, Moortown, Cookridge, Alwoodley or Roundhay. Fifteen to twenty square metres, three tired layers of felt, no scaffold needed, and a leak that has been quietly soaking whatever is stored underneath for years. That is a one-day job, and it should be priced like one.
The Leeds-specific warning is asbestos. Garages and outbuildings of that age often have cement sheeting, either as the roof itself on the prefabricated ones or as a lining. It is safe while it is intact and left alone, and it is not something to break up in the garden. It needs identifying before a strip is quoted rather than discovered halfway through one, and where it is there it belongs on the quote as a line of its own.
More on the work itself: flat roof repair and replacement for extensions and dormers, garage and outbuilding roofsfor the one-day version, and the new roof cost guide if the pitched roof above it is due at the same time.
Got a flat roof quote you want checking?
Send me a photo of the roof and the quote. I will tell you whether the number looks right for that roof, whether or not you use me.
Call 07770 902292Flat roof replacement cost: common questions
How much does it cost to replace a flat roof in the UK?
About £45 to £120 per square metre fitted, which is where all the published guides agree once you set their headline averages aside. That puts a single garage roof of 15 to 20 square metres at roughly £750 to £2,400 and a small rear extension at £600 to £2,160, before scaffolding and waste. The averages you see quoted, from £2,750 to £8,000, are the same rate applied to much larger roofs than most people have.
How much is a garage flat roof replacement?
A single garage is usually 15 to 20 square metres, so at the published rates it is about £750 to £1,600 in felt, £1,200 to £2,000 in EPDM rubber and £1,425 to £2,400 in GRP fibreglass. It is the cheapest flat roof job there is because it almost never needs scaffolding, and it is normally one day of work. Check whether the deck is included: on a garage of that age the boards are often the real job.
Is it better to repair or replace a flat roof?
The deck decides it, not the covering. If the boards are dry and the leak is at a trim, an upstand or an outlet, a repair will hold for years and costs a fraction of a replacement. If the deck is soft underfoot, or the leak appears somewhere different each time, water has been getting in long enough that a repair is money spent twice. Anybody who quotes a replacement without walking on the roof has not checked.
What is the cheapest flat roof covering?
Torch-on felt, at roughly £50 to £80 per square metre, and it is a reasonable choice on a garage or an outbuilding where a shorter life does not matter much. On an extension over a room you live in, the twenty to thirty years an EPDM or GRP roof gives is worth the extra, because the cost of the next replacement is not just the roof, it is the ceiling underneath it.
How many days does it take to replace a flat roof?
A single garage is usually one day. A small extension is one to two. A full-width extension or anything needing new decking runs to three or four, and scaffolding adds a day at each end that is not roofing at all. GRP needs the weather to cooperate on the day it goes down, so a wet week moves it.
How often do flat roofs need replacing?
Felt is ten to twenty years, EPDM rubber and GRP fibreglass twenty to thirty. In practice most of them fail earlier than the material should, and almost never in the middle: it is the upstands, the trims and the outlets that go, which is detailing rather than material. A flat roof that was detailed properly usually reaches its stated life, and one that was not usually does not see half of it.
Can you claim for a new flat roof on house insurance?
For sudden damage, such as a storm lifting a covering or a tree coming down on it, usually yes. For a roof that has simply worn out, no: gradual deterioration and lack of maintenance are excluded on almost every policy. That is why storm damage gets photographed before anything is touched, and why an insurer asking when the roof was last inspected is not an idle question.
Where the published figures come from
- Federation of Master Builders, flat roof replacement cost guide
- Checkatrade, flat roof replacement costs
- MyJobQuote, flat roof replacement cost
- Rubber Roofing Direct, average cost to replace a roof
- Knights Roofing, flat roof replacement price guide
- Per-material rates are the range those guides agree on, read from the results page for "flat roof replacement cost" on 17 August 2026
Figures were read from these guides in August 2026. They move, so treat any number here as the shape of the answer rather than a quote. The only price that binds anybody is one written down after somebody has stood on your roof.
Get in touch
Get a free quote from a local roofer.
Tell me what you need and I'll get back to you to arrange a look.