A kitchen extension turns the darkest, most cramped part of an older house into the room the whole family lives in. It is also a project where the design and the build are bound up together: drainage, steels, glazing, extraction and the kitchen itself all depend on one another. That is why we run it as one job with one price, rather than an architect's drawing handed over the wall to a builder.
The Extension Company is the extensions studio of Pine Grove Design & Build Ltd. We work across London, North London first, where the houses shape the kitchen schemes: Victorian and Edwardian terraces where the kitchen sits in a narrow back addition beside a side passage, and 1930s semis where it is a small room at the back next to a separate dining room.
The three kitchen extension types
The rear kitchen extension. The back wall moves out 3 to 6 metres and a full-width kitchen-diner opens onto the garden. On a 1930s semi it joins the small back kitchen and the dining room into one room. Permitted development allows 3m on a terrace or semi and 4m on a detached house, or 6m and 8m through prior approval. The build costs £45,000 to £90,000, plus the kitchen. Our guide to single-storey and rear extensions covers the extension itself in more depth.
The side-return extension. Victorian and Edwardian terraces waste a strip of side alley beside the back addition. Building into it turns a galley kitchen into a proper room without touching the garden. Build cost is £35,000 to £65,000, and the glazing over the infill (roof lights or a continuous glazed strip) decides how the room feels. The detail, including party wall notices, is on our side return extensions page.
The wrap-around. Side return and rear extension combined into an L: the full open-plan rework of the ground floor, usually £70,000 to £140,000 build cost. A wrap-around has to meet the rear and the side limits of permitted development at the same time, so it often goes to a full planning application.
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 a typical 20m² kitchen extension with a mid-range kitchen is £75,000 to £110,000. Our 20m² kitchen extension guide goes through that size line by line, and what actually drives kitchen extension costs explains why two kitchens with the same footprint can price a long way apart. The North London cost guide covers every size and route, and the Extension Builder prices your own dimensions in 60 seconds.
Moving the kitchen: the part that needs designing first
Many kitchen extensions also move the kitchen, out of a cramped middle room and into the new space, or to a new position in a reworked layout. That is a services job as much as a building one. Drainage runs and soil connections decide where the sink and dishwasher can go, gas and electrics get rerouted, and extraction from the hob has to reach an outside wall without a ceiling full of boxing. Where the new room goes over or within 3 metres of a public sewer, Thames Water has to agree to the build-over before work starts. These decisions belong on the drawings, not on site: moving a soil connection after first fix is how budgets slip. Our building regulations drawings fix every service run before anyone lifts a tool, which is what 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 lets the old back wall vanish into one open span with a flush ceiling. The light: roof lights over the worktops and glazed doors to the garden, with glass placed where the plan needs it rather than where a brochure put it. The threshold: level access to the garden and one floor finish running through. We design all three before pricing, so the quote you sign already contains the scheme you want.
Planning permission for kitchen extensions
Many single-storey kitchen extensions need no planning application. Under permitted development a rear extension can go 3m beyond the original back wall of a terrace or semi, or 4m on a detached house, up to 4m high, with eaves no higher than 3m within 2m of a boundary. Extensions and outbuildings together must not cover more than half the garden. The prior-approval route for larger home extensions stretches the depth to 6m and 8m: the council consults the neighbours and has 42 days to decide. A single-storey side return can also be permitted development if it is no higher than 4m and no wider than half the original house. Flats and maisonettes have no householder permitted development rights, and some newer houses lost theirs through a condition on the original planning permission.
Conservation areas change the picture. On conservation-area land a side extension is never permitted development and the prior-approval route is closed, so a side return or a deep rear kitchen needs a householder application. North London's conservation areas include Southgate Green, Winchmore Hill Green, Muswell Hill, Highgate, Crouch End and Wood Street in Barnet, among others, and Enfield's Article 4 directions over Southgate Green and Winchmore Hill take away further rights. Our conservation area guide explains what that means for a design.
Whatever the route, we secure the paperwork: a Lawful Development Certificate for a permitted-development scheme, prior approval or a full application where needed. Building regulations approval applies either way. If you are building on the boundary with an attached neighbour, or digging within 3 metres of their house and below its foundations, the Party Wall etc. Act 1996 needs notices served one to two months ahead; our party wall guide sets out the timings. Every planning fee is itemised in our planning fees guide, and further down this page are the councils' own decisions on single-storey rear and side-return applications, taken from the public planning records.
How long does a kitchen extension take?
Design and drawings take two to three weeks from survey. A planning application, where one is needed, adds the council's eight-week decision period, and prior approval up to 42 days; permitted-development schemes skip both. The build runs three to four months, with the kitchen fitted in the final weeks. The long-lead items (steels, glazing, and the kitchen itself at six to twelve weeks) are ordered against the programme so the site never stands waiting. Expect to be without a working kitchen for six to eight weeks mid-build; we plan a temporary setup so the house keeps functioning.
If what you are picturing has brick piers and a roof lantern rather than a solid roof, you are describing an orangery: the same room in a different architecture, and we do both.
What clients say
“The Extension Company built a 5m single storey rear extension on our Victorian terrace in Crouch End. Went down the permitted development route so no planning application needed, which they explained up front and saved us months. Kitchen-diner now opens onto the garden with sliding doors. £87k all in, matched the quote.”
“Our wrap-around extension has completely transformed the ground floor. We now have the open plan kitchen and family space we wanted without losing all of the garden. Thanks to everyone involved.”
More reviews from our Google profile, shown word for word, are on our testimonials page.