Anyone searching for flat roof cost wants a single figure, and the honest answer is a range with a long list of reasons it moves. A small porch canopy and a double-width rear extension are both flat roofs, but they share very little beyond the name. The price depends on how many square metres you have, which covering goes on, what state the deck is in, how much insulation the roof needs, and how hard the roof is to reach. This guide gives the typical UK ranges reported by cost guides, shows how to turn them into a rough budget for your own roof, and explains the items that surprise people once the old covering is off.
Typical UK ranges per square metre
Cost guides quote flat roofs by the square metre, supply and fit. We do not publish a Beacon price list, because the price of your roof follows the survey, but the published ranges give you somewhere to start. One consumer cost guide reports felt at £60 to £100 per m², with EPDM at £80 to £120 per m² and GRP at £100 to £160 per m². A trade-facing guide, written for contractors, reports EPDM at £70 to £100 per m², GRP at £80 to £120 per m² and modified bitumen felt at £45 to £75 per m². The two sets do not match, and they are not meant to: they come from different sources, with different assumptions about what is included.
| Covering | Typical UK range, consumer guide | Typical UK range, trade guide |
|---|---|---|
| Felt | £60 to £100 per m² | £45 to £75 per m² (modified bitumen) |
| EPDM | £80 to £120 per m² | £70 to £100 per m² |
| GRP | £100 to £160 per m² | £80 to £120 per m² |
Treat these as national orientation figures from third-party guides, many of them written by lead-generation or trade sites. Once we have surveyed your roof you get a fixed written price for that roof, which will differ from any average here.
Turning a range into a rough budget
Measure the roof outline in metres, multiply length by width, and you have the area. A rear extension roof measuring 4 m by 3.5 m is 14 m². At the consumer-guide range for EPDM, that works out at roughly £1,120 to £1,680 for the covering alone. At the GRP range it is roughly £1,400 to £2,240. Those sums are arithmetic on the published ranges, not a quote, and they leave out everything on the list that follows.
A small garage is a useful cross-check. One guide gives a typical fitted range for an EPDM single garage roof of £1,200 to £2,500, which is consistent with a roof of around 15 to 20 m² once the edges are included. The point is that small roofs cost more per square metre than large ones, because the fixed work, such as setting up, forming the edges and clearing away, does not shrink in proportion.
What moves the price up
The covering is only one line in the bill. These are the items that usually push a flat roof quote higher than the headline per-metre figure suggests:
- A rotten deck. If the boards under the old covering are wet or soft, they have to be replaced before anything new goes on. We cannot know until the covering is lifted, though a survey from above and below often gives a strong indication.
- Lost falls. A roof that holds water needs its slope rebuilt, using tapered timber firrings (strips cut to a slope) or tapered insulation boards. That adds material and labour.
- Insulation. Replacing a flat roof covering, as opposed to overlaying it, generally brings an insulation upgrade into the job. A warm roof means rigid boards above the deck, and the thicker the board, the higher the cost.
- Detailing. Rooflights, vents, soil pipes, wall abutments and a parapet each need hand-formed details. A roof with six penetrations costs more than a clear rectangle of the same area.
- Edge trims, outlets and gutters. New trims and a proper outlet are cheap compared with a leak, but they are lines on the quote.
- Access. A roof reached by a ladder from a ground-floor extension is simple. A roof over a first-floor bay may need a scaffold tower or a full scaffold, and scaffold can be a significant figure in its own right.
- Waste. Old felt is heavy, and the cost of removal and disposal is in every honest quote.
Overlay or strip: the biggest single choice
Laying a new covering over the old one is quicker and cheaper at first, and in the right circumstances it is a sound approach. It only works if the existing roof is dry, flat enough, firmly fixed and not holding moisture in the insulation. Overlaying a wet roof seals the damp in and shortens the life of the new layer. It also does not usually trigger the insulation upgrade that comes with replacing a covering, so the saving is partly a saving on insulation that a stripped roof would have to include.
Stripping back to the deck costs more because it adds removal, disposal, deck repairs, and insulation. It also lets us see what is really there, put right problems that were hidden, and build the roof with correct falls. For a roof that is well past its best, a strip is usually the better use of money. Our guide to flat roof repair or replacement explains how we decide, and the answer on overlaying a flat roof covers the technical limits.
Cheaper is not always cheaper
The cheapest way to cover a flat roof is felt, and for a short-term situation, such as a house you plan to sell, it can be the honest recommendation. Over a long ownership the cost per year often favours the more durable coverings. A felt roof that needs replacing twice in the time an EPDM or GRP roof needs doing once is not the bargain it looked like on day one. What shapes that is covered in our flat roof lifespan guide, and the short answer on the cheapest roofing for a flat roof looks at the low end.
It is also worth being wary of a price that is far below the rest. A quote that omits the deck check, the insulation, the edge trims or the waste removal looks cheaper until the missing items turn up as extras. Ask each contractor to put the same things in writing so the prices can be compared properly: the area, the covering, the insulation thickness, the edge trims, the details at walls and rooflights, and what happens if the deck is found to be bad.
Building Regulations and the cost of getting it wrong
The Planning Portal sets a test for re-roofing work. Small jobs stay outside the building control process, and bigger ones do not: the Planning Portal ties the dividing line to how much of the whole building and how much of the roof is affected. Cross it and approval is required, and the insulation across the entire roof may have to be improved, which is a cost worth knowing about before you commit. Weight is a separate trigger. If the new surface is noticeably heavier than the old, approval can be needed and the structure may need strengthening, which matters if you are thinking about paving or a planted roof. Where an application is needed we deal with the paperwork for you, and any fee is itemised in the quote instead of turning up later. If you are unsure, your building control body or your council's planning team can confirm what applies to your roof.
Where the money goes on a typical extension roof
It helps to picture a quote as layers rather than one number. At the bottom is access and preparation: getting safely on to the roof, protecting the walls and windows below, and stripping the old covering. Next comes the structure: repairing any damaged deck boards and building up the falls. Above that sits the insulation, which on a replacement is often the largest material cost after the covering itself. Then comes the covering, with its adhesive, primer or resin. Last are the details: trims, flashings, outlets and finishing around anything that pokes through the roof.
The reason this matters is that only one of those layers appears in a per-metre price. Two roofs of identical size can sit at opposite ends of a range because one is a straightforward rectangle on a dry, level deck and the other has a leaking rooflight, a lost fall and a rotten edge board. We would rather explain that to you with photographs than hide it in a lump sum.
Repairs, patches and coatings
Not every flat roof job is a replacement. A split at an upstand, a failed outlet seal, a lifted edge trim or a puncture can often be repaired for a small fraction of the cost of a new roof. A liquid coating can renew a tired but sound surface. We recommend these where they make sense, and the survey is how we tell the difference. Paying for a repair on a roof that is finished is a waste, and paying for a new roof where a repair would do is worse, so we say plainly which situation you are in.
How to compare quotes and get a fixed price
A fixed written quote should state the area, the covering and its thickness or build-up, the insulation, the treatment of the deck, the edge and outlet details, the waste arrangements and the guarantee. Anything left as an allowance or "subject to inspection" should be explained. We start with a free survey, where we go up, look at the deck, falls, outlets, edges and junctions, and photograph what we find. You see the pictures and get a plain description of what needs doing and why, then a fixed price for that work.
Where we recommend a new roof, we put a ten-year guarantee in writing, and the site is left tidy. If you would like the figures for your own roof rather than a national average, tell us about it through our flat roofing in Basingstoke page or on 01256 213956, and we will arrange the survey.
