Kitchen Extensions in London: Costs, Layouts and What to Expect

Most people don’t set out to extend their house. They set out to fix the kitchen.

It usually starts the same way. The kitchen sits at the back, it faces north, and it was laid out for someone who cooked with the door shut. There’s a wall between you and the dining room. There’s another between you and the garden. You’ve measured it twice, moved the fridge on paper four times, and there is no arrangement of units that makes the room work.

So you stop thinking about units and start thinking about walls.

That’s how most of our house extension jobs begin. Not with an architect’s drawing, but with someone standing in a cold back room in February, working out that the problem isn’t the cupboards.

What you actually get

Three things, roughly in this order: light, space, and a room the household ends up living in.

Light does more work than people expect. On a job in Chiswick we took down an old rear structure — small, cold, not very practical — and rebuilt it from the footings up with a flat roof and two skylights. The floor area went up, but that wasn’t the change people noticed when they walked in. It was that the back of the house stopped being dark on a grey London day.

Space is the obvious one, though it’s worth being precise about how much. A typical London rear extension adds somewhere between 12 and 25 square metres. That is not a vast amount. It is enough for a proper table, an island, and a run of units without anyone reversing into anyone else.

Then there’s value, which gets quoted a lot and understood rarely. A good kitchen extension usually returns a solid share of what it cost when you sell — but the return depends on the area and the finish, not on the fact that you extended. An extension that’s badly detailed or too big for the plot can put buyers off rather than draw them in.

The three layouts that work in London homes

Almost every kitchen extension in London is one of three shapes. Which one suits you is decided mostly by the house, not by preference.

Rear extension

Straight out the back, into the garden. This is the standard option for a terrace or semi, and usually the most straightforward to build. You lose garden depth and gain room width.

Works well if your garden is long enough to give some up, and if the existing back wall isn’t carrying anything complicated.

Side return

The narrow strip down the side of a Victorian terrace — the one currently holding a wheelie bin and a dead plant. Filling it in doesn’t sound like much, but it squares off an awkward L-shaped room, and it costs you no garden depth at all.

The catch is that side returns are fiddly. Narrow access, a party wall on one side, and drainage that usually runs exactly where you want to build.

Wraparound

Both at once — side return plus rear. The biggest gain and the biggest bill. Worth it if you’re going to be in the house for years and the kitchen is genuinely the centre of it.

What it costs in London

Costs move with materials and with which part of London you’re in, so treat these as a starting range rather than a quote. Everything below is build cost. Kitchen units, appliances and worktops come on top, and they vary more than the building work does.

Add roughly 10–15% for architect and structural engineer, plus council fees. Add VAT. And set aside a contingency of around 10% — on an older house you will find something. Cracked drains, a foundation that stops earlier than anyone expected, a wall that turns out to be doing more work than it looks like it’s doing.

What pushes a job to the top of its range is usually structural: deeper footings, longer steel spans, moving drainage. Big sliding doors and a roof lantern add cost too, but they’re a choice. Groundwork isn’t.

Planning permission, and the bit people forget

A lot of single-storey rear extensions fall under permitted development, which means no full planning application. For a terraced or semi-detached house that’s generally up to three metres out from the original rear wall, four for a detached. There’s a larger scheme that takes you to six and eight metres, but it needs prior approval from the council and your neighbours get consulted.

Height is capped at four metres, and if you’re building within two metres of a boundary the eaves have to stay under three.

Conservation areas and listed buildings are a different conversation entirely, and plenty of London streets are in one. Always check before you fall in love with a drawing. Rules also change, so what a neighbour got away with in 2019 isn’t a guide. Our planning and design team handles this part for clients, mostly because it’s the stage where a job either sets off smoothly or gets stuck for three months.

Then there’s the bit people forget: permitted development is not the same as building regulations, and you need to satisfy both. Building control cares about structure, insulation, drainage, fire escape and ventilation. That’s a separate approval and a separate inspection.

And if you share a wall with next door — which in a London terrace you do — the Party Wall Act applies. Serve notice early. Two months’ notice is the requirement, and a neighbour who first hears about your project when the skip arrives is a neighbour who takes their time.

How long it takes

Longer than the build, which is the part that surprises people.

Design, drawings and structural calculations take four to eight weeks. Planning, if you need it, is eight weeks minimum from validation and often longer. Building regs approval runs alongside. So you’re realistically three to five months from first conversation to first spade in the ground.

The build itself, for a straightforward rear extension, runs ten to sixteen weeks. Groundwork and foundations take the first two to three, and that stage looks slow because it is slow. On the Chiswick job the footings had to go deeper than the original, so we dug out, poured new reinforced concrete, and dealt with the drainage inside and out before anything went up. It was a slow process. It was also the part that everything else depended on.

Then structure, roof, and the point at which it starts looking like a room. Insulation, slab, membranes, screed. Plasterboard, skim, floor.

Fit-out — the actual kitchen — comes last and needs three to four weeks of its own. Plumbing and electrics get first fixed while the walls are open, which is why the layout has to be decided before then. More on that below.

Mistakes we see most often

Leaving the kitchen layout until the building work is nearly done. Sockets, water, waste and extraction all get roughed in while the walls are open. Change the island position in week nine and something has to be chased back out again. Decide the layout at drawing stage, even if the units get chosen later.

Underestimating the ground. Old drains, shallow foundations, a neighbour’s extension already sitting on the boundary — none of it shows up on a survey drawing. It shows up on day four.

Glazing without thinking about summer. A big south-facing roof lantern is glorious in March and punishing in July. Solar-control glass, or blinds, or a smaller opening in a better place.

Skimping on insulation because it disappears behind plasterboard. It’s one of those things you don’t see, and it’s the difference between a room you use in January and a room you shut the door on.

Choosing on price alone. A quote well under the others usually means something has been left out, and you’ll meet it later as a variation.

Frequently Asked Questions

How much does a kitchen extension cost in London?

Build cost typically runs from around £45,000 for a small rear extension to £165,000 or more for a wraparound, before kitchen units, appliances and VAT. The main variables are groundwork, steel spans and glazing. We’d always rather look at the house before giving a figure.

Do I need planning permission for a kitchen extension?

Often not. Many single-storey rear extensions fall under permitted development — generally up to three metres for a terrace or semi, four for a detached house, with a larger scheme available through prior approval. Conservation areas and listed buildings are the usual exceptions. Building regulations approval is always needed, whether or not planning is.

How long does a kitchen extension take to build?

Ten to sixteen weeks on site for a standard rear extension, plus three to five months beforehand for design, planning and approvals. Fit-out of the kitchen itself adds three to four weeks at the end.

Can I stay in the house during the work?

Usually yes, though not comfortably for the whole stretch. The back of the house is open to the weather for part of the build, and you’ll be without a kitchen for several weeks. Most clients set up a temporary kitchen elsewhere in the house. Some move out for the messiest four weeks and come back.

Does a kitchen extension add value to a London property?

Generally yes, though not pound for pound in every case. A well-proportioned extension with a good finish in a decent area usually returns most of its cost and sells the house faster. An extension that eats the entire garden, or one that’s obviously cheaply built, can do the opposite.

What’s the difference between a rear extension and a side return?

A rear extension goes straight out into the garden and adds depth. A side return fills the narrow alley beside a Victorian terrace and adds width, squaring off an awkward room without costing you garden. A wraparound does both.

Thinking about it?

If you’re at the stage of standing in a cold back room with a tape measure, that’s the right time to talk. Early conversations save money, because the expensive decisions — where the steel goes, where the drains run, how far out you can build — all get made before anyone commits to a drawing.

We’ve been building across London for over 25 years. You can see a full rear extension we took from demolition to finish in our Chiswick project, or read more about our kitchen and bathroom work.