Kitchen Extension Costs and Ideas in London 2026

The kitchen extension is London's most popular home-improvement project, and for good reason. Knocking through to a rear or side-return extension turns a cramped, dark galley kitchen into the open-plan kitchen-diner most families actually want, and it reliably adds value in London's market.

But costs vary widely depending on the type of extension, the glazing, and the kitchen specification. Below are realistic 2026 prices based on projects we deliver across London, what each one includes, the design choices that make the biggest difference, and where the budget really goes.

Kitchen extension types and costs

The shape and size of the extension is the single biggest cost driver. Here is what each type typically costs in London in 2026, fully built:

Extension type	Typical cost	Best for
Single-storey rear	£40,000 – £75,000	Most terraces and semis
Side-return	£45,000 – £80,000	Victorian terraces with a side alley
Wraparound (L-shaped)	£70,000 – £110,000	Maximum kitchen-diner space
Double-storey (room above)	£85,000 – £140,000	Adding a bedroom or bathroom too

What is included in the build price

When Alstruct quotes a kitchen extension, the price covers everything needed to deliver a watertight, finished shell, ready for your kitchen install:

• Groundworks and foundations — excavation, footings and a new insulated concrete slab.
• Structure — steel beams to open up the rear wall, blockwork, and the new roof.
• Glazing — bi-fold or sliding doors, roof lights or a lantern, all double-glazed.
• Roof — warm flat roof, lantern or pitched roof, fully insulated to Part L.
• Electrics and plumbing — full wiring, lighting, sockets, and moving services for the new layout.
• Heating — underfloor heating or radiators tied into your existing system.
• Plastering, screed and decoration — walls and ceilings finished and painted, ready for flooring and the kitchen.
• Building Control — all inspections managed and the Completion Certificate obtained for you.

What drives the cost up or down

Glazing choices

Glazing is where budgets swing most. A modest set of bi-fold doors and a couple of roof lights is far cheaper than a full structural-glass lantern, sliding pocket doors and a glazed roof. Crittall-style screens and slimline aluminium frames sit at the premium end.

Structural work

Removing the entire rear wall for a fully open-plan space needs more steel, and sometimes a goalpost frame, than keeping a section of wall. Side-returns over shared drains may also need the drainage diverted, which adds cost.

Kitchen specification

The units and appliances are a separate budget from the build, and they range enormously, from around 8,000 pounds for a quality off-the-shelf kitchen to 40,000 pounds or more for bespoke cabinetry, stone worktops and integrated appliances.

Location and access

Tight inner-London access, parking suspensions and no rear access all add to scaffolding, skip and delivery costs. Conservation-area requirements such as matching brick and specific windows can also raise the spend.

Design ideas that make a kitchen extension work

• Roof lights or a lantern — the best way to flood a deep-plan kitchen with daylight, especially in a terrace where you cannot add side windows.
• Bi-fold or sliding doors to the garden — opening the kitchen to outside makes even a modest extension feel generous.
• An island — if you have the width, an island gives prep space, storage and a social hub.
• Broken-plan, not just open-plan — a part-wall, a step or a change in ceiling height zones the spaces without closing them off.
• Continuous flooring — running the same floor through to the garden doors makes the whole space read as one.

Do you need planning permission?

Many single-storey rear and side-return kitchen extensions fall under permitted development, so no planning application is needed, provided you stay within the size limits and are not in a conservation area or Article 4 zone. Wraparound and double-storey extensions almost always need full planning permission. Either way, the work must meet Building Regulations, and we handle that for you.

How Alstruct delivers your kitchen extension

We are a genuine design-and-build contractor, so one team handles the drawings, structural engineering, the planning or permitted-development route, and the construction itself. That removes the gaps and finger-pointing that come from juggling an architect, an engineer and a separate builder, and it keeps your project on a single, accountable timeline, backed by our 10-year workmanship warranty.

Frequently Asked Questions