A kitchen extension in London is usually priced per square metre of new floor area and the published rates sit between roughly £1,650 and £3,500 per square metre depending on which guide you read and whether VAT and professional fees are included. At London and Kent Construction we price each job from measured drawings rather than from a rate.
The honest starting point is that the published guides disagree with each other and in one case with themselves. Checkatrade, in a kitchen design cost guide its page says was last updated in May 2024, puts the average cost of a kitchen extension at around £30,000. Resi, on a London kitchen extension cost page dated 13 February 2026, says the cost "can vary anywhere between £40K to £200K". Both are reputable. Neither is wrong. They are measuring different jobs and this article separates them out.
Why published kitchen extension costs vary so widely
Published kitchen extension costs vary because the guides measure different things and rarely say so on the same line. Four variables move the number before a single brick is laid. The first is whether the figure covers the shell only or the shell plus the fitted kitchen. The second is whether VAT is included: Resi's per square metre rates are quoted excluding VAT and Checkatrade's kitchen diner rates are also quoted excluding VAT. The third is whether professional fees are in or out and Checkatrade's kitchen design guide states its per square metre rates exclude them. The fourth is London. Most national guides publish a UK figure and then add a London uplift, or no uplift at all. When you compare a London figure that includes a kitchen against a UK figure that excludes VAT and fees, you can produce a gap of well over £50,000 without either source being inaccurate.
Kitchen extension cost per square metre, UK and London
Per square metre rates are the most useful way to compare kitchen extension costs, provided you note what each rate excludes. Checkatrade's kitchen design cost guide, last updated May 2024, gives a single storey standard extension in the UK at £1,650 to £2,300 per square metre with an average of £1,975 and the same extension in London at £2,025 to £2,925 per square metre with an average of £2,475, in both cases excluding professional fees. Checkatrade's kitchen diner extension guide, also last updated May 2024, gives a lower range of £1,500 to £2,000 per square metre excluding VAT, around £1,750 per square metre, while repeating the £1,650 to £2,300 figure for a single storey kitchen extension excluding professional fees. Checkatrade's house extension guide, dated 2025, advises budgeting £1,800 to £3,000 per square metre and states plainly that kitchens cost more than standard rooms. Resi puts the construction cost of an extension in 2025 at £2,200 to £3,500 per square metre excluding VAT and says that in London and the surrounding areas it will be at the upper end of that range.
What a 20, 30 and 50 square metre kitchen extension costs on published figures
Total costs for a kitchen extension are published by floor area as well as by rate and the two do not always reconcile. The list below sets out the published totals side by side, with the publisher named on each row so you can see where each figure comes from.
- 12 m² kitchen extension: £15,000 to £24,000, average £19,500 (Checkatrade house renovation guide, September 2026)
- 20 m² kitchen extension: £30,000 to £40,000 (Checkatrade kitchen diner guide, May 2024)
- 20 m² single storey extension: £40,000 to £56,000 (HomeOwners Alliance renovation cost guide, page dated 4 September 2026)
- 20 m² single storey extension: £40,000 to £55,000, average £48,000 plus VAT (HomeOwners Alliance extension cost guide, page updated July 2026)
- 30 m² single storey extension: £60,000 to £84,000 (HomeOwners Alliance (September 2026) and Checkatrade (2025))
- 50 m² single storey extension: £100,000 to £140,000 (HomeOwners Alliance, page dated 4 September 2026)
The 20 square metre rows are the clearest illustration of the problem. Checkatrade's kitchen diner guide, last updated May 2024, gives £30,000 to £40,000 for a 20 square metre kitchen extension, while the HomeOwners Alliance renovation cost guide, on a page dated 4 September 2026 and itself attributing Checkatrade, gives £40,000 to £56,000 for a 20 square metre single storey extension. The same organisation's separate extension cost guide, updated July 2026, gives £40,000 to £55,000 for the same 20 square metres and an average of £48,000 plus VAT. That is two pages from one publisher, a year apart, £1,000 apart at the top of the range. It is a fair illustration of how much precision these figures actually carry. Note too that the HomeOwners Alliance figures are for a single storey extension generally rather than a kitchen extension specifically and that neither page adds a London uplift. Use the rows as brackets, not as quotations for your own job.
The kitchen itself is a separate budget line
The fitted kitchen is a separate cost from the kitchen extension that houses it and mixing the two is the most common budgeting error we see. Checkatrade, in its May 2024 kitchen design guide, says the kitchen itself will usually start from around £5,000 for a basic model and puts adding a new basic kitchen to a basic extension at £5,000 to £6,000, averaging £5,500. Checkatrade's house renovation guide, last updated September 2026, gives a wider £7,000 to £25,000 for a new kitchen, typically including design, materials and fitting. The HomeOwners Alliance, on its page dated 4 September 2026, puts a new kitchen at £10,000 and upwards, notes that the average is between £10,000 and £20,000 and adds that 10 per cent of people spend over £50,000. Resi, in 2025 guidance, gives £5,000 to £30,000 for the kitchen and more again for one made to order. Checkatrade's house extension guide, dated 2025, approaches it from the other direction and suggests adding an extra £15,000 to £35,000 for the kitchen on top of the average extension cost.
Side return extensions, the common London kitchen job
The side return extension is the most common kitchen extension in London, because it fills the narrow strip of ground beside the rear closet wing of a Victorian or Edwardian terrace. Published figures for it vary by the size of the contractor as much as by the size of the extension. Resi's London kitchen extension cost page, dated 13 February 2026, gives a 30 square metre London side return kitchen extension, excluding VAT, at £52,000 to £75,000 from an individual contractor, £63,600 to £90,000 from a small company and £68,250 to £97,500 from a large company. Checkatrade, in the same May 2024 guide, gives a small side return extension at £30,000 to £45,000. It is worth saying openly that Resi's separate side return kitchen extension advice page quotes approximately £80,000 to £120,000, which is above the top of its own London table. The two pages are both Resi and they give different figures. Treat the higher page as a fuller scope including the kitchen and finishes and ask any builder which of the two their quote resembles.
Professional fees, planning fees and surveys
Professional and statutory fees sit outside most published kitchen extension rates and need their own line in your budget. Checkatrade, in its May 2024 kitchen design guide, puts professional fees at usually around 10 to 15 per cent of the cost. Resi, in its current guidance, states that a traditional architecture practice typically charges 5 to 10 per cent of project cost, giving £3,750 to £7,500 on a £75,000 rear extension as its own worked example. Statutory planning fees are national and published by gov.uk: a householder planning application in England is £548 as indexed from 1 April 2026 and prior approval for a larger home extension is £249. These fees are reviewed annually, so check the current figure before you apply. On an older house a structural survey is money well spent before the design is fixed and the HomeOwners Alliance, on the same 4 September 2026 page, puts a full structural survey at £500 to £1,500.
What pushes a London kitchen extension above the published range
A London kitchen extension moves above the published ranges for reasons that are visible on site long before they appear in a quotation. Removing the rear wall of a terrace to open the kitchen into the extension means a structural opening, steelwork and temporary support. On a solid wall house the padstone and foundation work below it. A side return sits directly on a party wall, so notices and a party wall award may be required. Access is often through the house, which changes protection, dust control and the rate of progress. Drainage frequently runs where the new floor needs to be and the manhole cover in the side return has to go somewhere. Glazing is the single easiest way to double a budget: a run of slim framed sliding doors and a rooflight is a different order of cost from a set of standard French doors. Then there is what the house hides. Older London houses turn up failed lintels, sulphate attack in old concrete floors, live and abandoned services and, in the worst cases, work by a previous owner that was never approved. Our London renovation cost guide sets out the wider picture.
Contingency and the honest answer on programme
A kitchen extension budget needs a contingency and the published advice is consistent on roughly how much. Checkatrade, in its house renovation guide last updated September 2026, advises adding 10 to 15 per cent for unexpected costs. The HomeOwners Alliance, on its page dated 4 September 2026, advises setting aside around 10 per cent. On programme, the Federation of Master Builders, in guidance dated February 2026, gives about three months for smaller and simpler extensions, four to six months for most single storey extensions and six months and beyond for larger or double storey projects. Those are build durations and do not include design, planning determination or the wait for a contractor to be free. Our article on how long a house renovation takes in London separates the two.
How London and Kent Construction prices a kitchen extension
We price a kitchen extension from measured drawings and a site visit, not from a rate per square metre. We look at the rear wall and what is carrying it, the drainage, the party wall position, the access route and the state of the existing kitchen and floor. We then price the work in sections, so you can see the shell, the structural opening, the glazing, the services and the fitted kitchen separately and make decisions on each. Where an allowance is unavoidable, for example on a kitchen you have not chosen yet, we show it as an allowance rather than burying it. We do not quote a price for a kitchen extension before seeing the house. We would be cautious of anyone who does. We hold CHAS and Constructionline accreditation and are NHBC registered. One example: a rear kitchen extension of around 10 square metres to a small flat in Fulham, in the London Borough of Hammersmith and Fulham, cost around £40,000.
Frequently asked questions
How much does a kitchen extension cost in London?
Published London rates run from about £2,025 to £2,925 per square metre excluding professional fees, per Checkatrade in May 2024, to £2,200 to £3,500 per square metre excluding VAT, per Resi in 2025, with London at the upper end. Totals depend on floor area, glazing and the kitchen itself.
Does a kitchen extension need planning permission?
Not always. Many single storey rear extensions fall under permitted development or the larger home extension prior approval route, for which gov.uk gives a fee of £249 from 1 April 2026. Conservation areas, Article 4 directions and listed buildings change the position, so check your address first.
Is the fitted kitchen included in a kitchen extension quote?
Usually not and you should ask. Published kitchen costs run from around £5,000 for a basic model, per Checkatrade in May 2024, to £5,000 to £30,000 per Resi. Confirm whether your quote includes supply, fitting or neither.
How long does a kitchen extension take to build?
About four to six months to build and about three months for a smaller and simpler one, on February 2026 guidance from the Federation of Master Builders. That is the build only. Design, planning determination and waiting for a contractor all sit before it.
Why is my builder's quote higher than the online cost guides?
Online guides publish UK averages and most exclude VAT, professional fees or the kitchen. A quote for your house includes the structural opening, drainage diversions, party wall work, access constraints and the finishes you have chosen. Compare quotes against each other on the same drawings, not against a national average.
What to do next
If you are planning a kitchen extension in London, the most useful next step is a site visit. We will look at the rear wall, the drainage, the access and the party wall position, tell you what the job involves and where the cost sits and set out what we would need to price it properly. Call 020 8850 7064, email team@londonandkent.co.uk or book a site visit. If you are still choosing a contractor, our guide on how to choose a renovation builder in London covers quotes, contracts and insurance and our renovation and refurbishment page sets out how we work.