Kitchen Extension Cost in West London: 2026 Price Guide
A kitchen extension is the project West London homeowners ask us about more than any other – and the one where the price range is widest, because the room, the glazing and the kitchen itself all vary so much. This guide from GSM Builders Ltd, builders based in Hayes, gives realistic 2026 kitchen extension costs for Hillingdon, Ealing, Hounslow, Harrow and Slough, shows what the money goes on, and explains how to keep the budget under control.
Kitchen extension cost: the short answer
In West London a single-storey rear kitchen extension of 18–22 m² costs £50,000–£70,000 for the build, plus £12,000–£25,000 for a mid-range fitted kitchen, plus VAT and fees. A 6 m extension creating a 30–36 m² kitchen-diner runs £75,000–£110,000 before the kitchen. A side-return kitchen extension on a Victorian terrace costs £40,000–£60,000; a wrap-around £85,000–£130,000. All in, most families spend between £80,000 and £140,000 including the kitchen and VAT.
| Kitchen extension type | New floor area | Build cost (ex VAT, ex kitchen) | Kitchen | All-in typical (inc. VAT) |
|---|---|---|---|---|
| Side-return (terrace) | 8–12 m² | £40,000 – £60,000 | £12k–£25k | £70,000 – £105,000 |
| 3 m rear (semi/terrace) | 18–22 m² | £50,000 – £70,000 | £12k–£25k | £80,000 – £120,000 |
| 4–6 m rear (prior approval) | 24–36 m² | £65,000 – £110,000 | £15k–£30k | £100,000 – £170,000 |
| Wrap-around (side + rear) | 30–40 m² | £85,000 – £130,000 | £15k–£35k | £125,000 – £200,000 |
What the money goes on
A typical £60,000 build for a 20 m² rear kitchen extension in Hayes or Ealing breaks down roughly like this:
| Element | Share | Typical cost |
|---|---|---|
| Groundworks, foundations, drainage | 15% | £9,000 |
| Structure – steel beam, blockwork, brickwork | 20% | £12,000 |
| Roof – warm flat roof or pitched, with roof lights | 15% | £9,000 |
| Glazing – doors and windows | 15% | £9,000 |
| First fix – electrics, plumbing, heating | 10% | £6,000 |
| Insulation, plasterboard, plastering | 8% | £5,000 |
| Second fix, flooring, decoration | 10% | £6,000 |
| Site management, scaffold, skips, protection, Building Control | 7% | £4,000 |
The kitchen itself sits on top. A well-made mid-range kitchen (Howdens, Wren, Magnet trade ranges) with quartz worktops and integrated appliances is £12,000–£25,000 fitted; German or bespoke kitchens start around £30,000.
The five decisions that move a kitchen extension budget
1. Depth: 3 m or 6 m?
A 3 m rear extension is permitted development almost everywhere. Going to 4–6 m needs prior approval (a 42-day neighbour consultation) but roughly doubles the floor area for about 50–60% more money, because foundations, drainage and steel are largely fixed costs. On 1930s semis in Hayes, Ruislip, Hounslow and Greenford we build more 4 m and 5 m extensions than 3 m ones.
2. Glazing
Standard uPVC French doors: £1,500. A 4 m aluminium sliding door: £8,000–£12,000. A roof lantern: £2,500–£5,000. Slimline steel-look (Crittall-style) doors: £12,000+. Glazing is the single biggest lever in the budget and the easiest place to overspend.
3. Opening up the original house
Most kitchen extensions involve removing the old rear wall (a steel beam, included above) – but many families also want to remove the wall between the old kitchen and dining room to create one open-plan space. That second structural opening, with its own beam and engineer’s calculations, adds £3,000–£6,000.
4. Drains and manholes
A manhole where the extension is going means a sealed double-seal cover or a diverted drain with Thames Water build-over approval – £1,500–£4,000. We check this on the first visit.
5. Finish level
Underfloor heating (£80–£120 per m²), a polished concrete or micro-cement floor, integrated LED lighting and a utility room push a standard build 20–40% higher.
Kitchen extension costs by house type in West London
- 1930s semi (Hayes, Ruislip, Hounslow, Greenford, Harrow): 4–5 m rear extension with a wrap-around option using the side passage – £65,000–£95,000 build.
- Victorian terrace (Ealing, Acton, Southall, Hanwell): side-return plus 3 m rear as an L-shape – £75,000–£110,000 build. No side access adds 5–10%.
- Detached (Ickenham, Northwood, Iver, Windsor): 6–8 m rear extensions with larger glazing and a utility – £90,000–£140,000 build.
- Ground-floor flat / maisonette: always needs planning permission and freeholder consent; £45,000–£70,000 for a 3 m extension.
Planning, Building Regulations and the Party Wall Act
A 3 m rear kitchen extension on a house is permitted development; 4–6 m needs prior approval; anything larger, any double-storey element, and any home in a conservation area with an Article 4 direction (common in Ealing) needs a householder application. Party Wall notices apply whenever you build on or near the boundary. Building Regulations approval is always required and our engineer, drawings and Building Control liaison are included in every GSM Builders Ltd quote.
How to keep a kitchen extension on budget
- Decide the depth early – changing from 3 m to 4 m after drawings are done means redoing them.
- Fix the glazing specification before the quote; it is where budgets drift most.
- Buy the kitchen from a trade supplier through your builder – installation is smoother and the price is often lower than retail.
- Keep the old kitchen usable as long as possible; we normally build the shell first and only break through at the end, so you are without a kitchen for two to three weeks rather than three months.
- Hold a 10% contingency and do not spend it on upgrades in week one.
Kitchen extensions with GSM Builders Ltd
We design and build kitchen extensions across Hillingdon, Ealing, Hounslow, Uxbridge, Harrow and Slough – drawings, planning, structure, build, kitchen fitting and decoration under one contract, with a written itemised price and a 12-month warranty. See our house extension service and kitchen fitting service, or read the broader extension cost guide.
Kitchen extension cost FAQs
How much does a kitchen extension cost in the UK in 2026?
In West London a 3 m single-storey rear kitchen extension costs £50,000–£70,000 for the build, plus £12,000–£25,000 for the kitchen and 20% VAT – typically £80,000–£120,000 all in. Side-return extensions are £40,000–£60,000 for the build; wrap-arounds £85,000–£130,000.
How much is a kitchen extension per square metre?
£2,600–£3,600 per m² for a single-storey rear extension in West London, excluding VAT and the kitchen. Side returns are higher per m² (£3,500–£5,000) because they are small but still need foundations, steel and a glazed roof.
Do I need planning permission for a kitchen extension?
Not for a single-storey rear extension up to 3 m on a house (4 m detached). Extensions of 4–6 m use the prior-approval route. Double-storey extensions, flats and conservation-area homes with Article 4 directions need a full application.
How long does a kitchen extension take?
8–10 weeks on site for a 3 m extension, 10–12 weeks for 4–6 m, plus 2–4 weeks for drawings and any approvals. The old kitchen usually stays in use until the last two or three weeks.
Does a kitchen extension add value?
In West London a well-built kitchen extension typically adds 10–15% to a property’s value – often £50,000–£100,000 on a £500,000–£700,000 home – as well as making the house work far better day to day.
Can GSM Builders Ltd supply and fit the kitchen too?
Yes. We fit kitchens from trade suppliers or your chosen retailer as part of the extension contract, so the electrics, plumbing and worktop templating are coordinated with the build.
