The kitchen extension is the most-built extension in Britain for a reason: it converts the darkest, most cramped part of an older house into the room the whole family actually lives in. It's also the project where design decisions and build decisions tangle together most — drainage, steels, glazing, extraction and the kitchen itself all interlock — which is why we run it as one job with one price rather than an architect's drawing thrown over a wall to a builder.
The three kitchen extension types
The rear kitchen extension. The classic: push the back wall out 3 to 6 metres and put an open-plan kitchen-diner across the full width. On a terrace or semi this is usually permitted development up to 3m (6m with prior approval); on a detached house, 4m and 8m. Costs £45,000 to £90,000 for the build, plus the kitchen.
The side-return extension. Victorian and Edwardian terraces across London waste a strip of side alley; claiming it turns a galley kitchen into a proper room without touching the garden. Build cost £35,000 to £65,000. The glazing over the infill — roof lights or a glazed strip — is what makes these sing.
The wrap-around. Side return and rear extension combined into an L: the full open-plan rework, usually £70,000 to £140,000 build cost, and usually a full planning application. This is the scheme that changes what the whole ground floor is.
What a kitchen extension costs in London in 2026
Work to £2,800 to £4,200 per square metre for the build in North London (premium areas run higher), then add the parts a build price never includes:
| Item | Typical 2026 cost |
|---|---|
| Build, 15m² (3m × 5m rear) | £42,000 – £63,000 |
| Build, 20m² (4m × 5m rear) | £56,000 – £84,000 |
| The kitchen itself — units, worktops, appliances | £8,000 – £30,000 |
| Structural glazing / bifolds / roof lights | £3,000 – £15,000 |
| Professional fees, building control, party wall | £3,000 – £7,000 |
| VAT | 20% on most work |
A realistic all-in figure for the typical 20m² kitchen extension with a mid-range kitchen lands £75,000 to £110,000. The full breakdown by size and area — including what moves the price and how to compare quotes — is in our North London cost guide, and the Extension Builder prices your exact dimensions in 60 seconds.
Moving the kitchen — the part that needs designing first
Half the kitchen extensions we build involve relocating the kitchen — from a cramped middle room into the new space, or downstairs in a reconfigured layout. That's a services project as much as a building one: drainage runs and soil connections decide where sinks and appliances can live, gas and electrics get rerouted, and extraction has to reach an outside wall without a ceiling full of boxing. These decisions belong on the drawings, not improvised on site — moving a soil connection after first fix is how budgets die. Our building regs drawings pin every service run before anyone lifts a tool; it's the discipline that keeps a fixed price fixed.
Design details that separate good from ordinary
The difference between a kitchen extension and a great one is mostly decided in three places: the steel design (a well-engineered frame is what lets the old back wall vanish into one open span with a flush ceiling), the light strategy (roof lights over the work zone, glazed doors to the garden — glass placed where the plan needs it, not where the brochure showed it), and the threshold (level access to the garden, one floor finish running through). We design all three before pricing, which is why the quote you sign already contains the scheme you actually want.
Planning permission for kitchen extensions
Most London kitchen extensions need no planning application: single-storey rears sit inside permitted development up to 3m on terraces and semis (6m with the £249 prior-approval route) and 4m/8m on detached houses, with height limits at 4m. Conservation areas trim side-return rights on some streets, and flats have no PD at all. Whatever the route, we secure the paperwork — Lawful Development Certificate for PD schemes, full application where needed — and building regulations approval applies regardless. Every fee is itemised in our planning fees guide.
How long does a kitchen extension take?
Design and drawings take two to three weeks from survey; planning, where needed, adds the council's eight weeks (PD schemes skip it); the build runs three to four months, with the kitchen fitting in the final weeks. The long-lead items — steels, glazing, and the kitchen itself at six to twelve weeks — get ordered against the programme so the site never stands waiting. Expect to be out of a working kitchen for six to eight weeks mid-build; we sequence a temporary setup so the house keeps functioning.
If what you're really picturing has brick piers and a roof lantern rather than a solid roof, you're describing an orangery — same room, different architecture, and we build both.
Frequently asked questions
How much does a kitchen extension cost in London? £55,000 to £110,000 all-in for a typical 18–25m² rear kitchen extension with a mid-range kitchen in 2026, excluding VAT and fees. Side returns run £35,000 to £65,000 plus the kitchen. You get a fixed, itemised quote after a free design visit.
Do I need planning permission for a kitchen extension? Usually not. Most single-storey rear kitchen extensions fall under permitted development — up to 3m on a terrace or semi, 6m with prior approval, 4m/8m detached. We confirm your route free and certificate it with a Lawful Development Certificate.
Can I move my kitchen into the new extension? Yes — around half our kitchen extension projects relocate the kitchen. Drainage, gas, electrics and extraction are designed onto the drawings before pricing, so the move is engineered rather than improvised.
How long does a kitchen extension take? Three to four months on site for a typical rear scheme, plus two to three weeks of design and the council's eight weeks where a planning application is needed. Many schemes start sooner under permitted development.
What size kitchen extension do I need? The UK's most-built size is 3m × 5m (15m²) — enough for a proper kitchen-diner. A 4m × 5m gives a full-width kitchen-living space with an island. The Extension Builder prices both for your house in 60 seconds.
Is a kitchen extension worth it? The kitchen-diner is the single most value-relevant room in a London sale, and a well-built rear extension typically returns most or all of its cost in added value — while transforming how the house lives day to day. What it's worth to your specific street, we'll tell you honestly at the design visit.