Kitchen Extension Ideas: What's Possible and What It Costs

Good kitchen extension ideas start with the shape of your house, not a Pinterest board. The extension type that suits a Victorian terrace with a side alley is completely different from the one that works on a 1930s semi with a wide rear garden, and the cost gap between them is large. Get the type right first and the design, light and budget all follow more easily.

This guide runs through the main extension types, what each one is good for, and what they realistically cost in 2026, with a clear note on the London premium. The figures are honest ranges to plan against, not quotes; every project turns on your specific house, spec and build team.

Single-storey rear extension: the classic choice

Pushing straight out into the garden is the most common way to enlarge a kitchen. It suits almost any property with garden depth to spare, and it gives you one clean, open span to work with, ideal for a kitchen-diner with an island and a run of glazed doors onto the garden.

Across the UK a single-storey rear kitchen extension typically runs £30,000 to £70,000. In London the same project usually lands between £80,000 and £150,000 all in, because build rates, glazing and 20% VAT push the per-square-metre cost to roughly £2,800 to £5,500. The variables that move the number most are the glazing (large sliding or Crittall-style doors are expensive), the roof (a lantern or full glass roof adds cost and light), and the kitchen specification itself.

Side return extension: the terrace specialist

If you own a Victorian or Edwardian terrace, the narrow alley running alongside the kitchen (the side return) is usually dead space. Filling it in widens a cramped galley kitchen into a proper room, often transforming the layout without eating much garden.

A side-return extension typically costs £35,000 to £60,000 nationally, and more in London. Because the footprint is modest, the money goes on structure and, above all, roof light: a glazed roof or a run of roof lanterns is what stops the new, deeper room from feeling dark. It is one of the highest-impact extensions per pound spent, which is why it is so popular in inner-London boroughs.

Wrap-around extension: rear and side combined

A wrap-around does both at once, extending into the garden and filling the side return in an L-shape around the back of the house. It delivers the biggest single jump in floor area and lets you design a large open-plan kitchen, dining and living space in one go.

Budget £60,000 to £100,000 across the UK, or roughly £90,000 to £170,000 in London where per-square-metre rates sit around £3,200 to £4,800. It is the most disruptive option and the one most likely to need careful structural work, so it rewards a good architect or designer and a realistic timeline.

Glass box and roof lantern ideas: light over floor area

Sometimes the goal is not more space but more light and a better connection to the garden. A frameless glass box on a period property, a flat roof with a large roof lantern, or a “Crittall” grid of steel-framed glazing can turn an ordinary extension into the best room in the house.

Glazing is where budgets stretch fast: a modest 25 square metre rear extension in West London that included a glass roof section and Crittall-style doors came in around £92,000 for construction alone in early 2026. If light matters more than square metreage, spend it on the roof and the doors rather than on footprint.

Orangery: between a conservatory and a full extension

An orangery, with solid corners, a lantern roof and generous glazing, sits between a conservatory and a full brick extension. It feels like a proper room year-round, unlike an old-style conservatory, while bringing more character and light than a flat-roofed box. It suits homeowners who want a softer, more traditional look and are happy to pay for the glazing and the lantern.

What actually drives the cost

Whichever type you choose, the same few things move the budget:

• Glazing. Sliding doors, steel-framed glazing and glass roofs are the single biggest swing factor.
• Structure. Removing a load-bearing wall for open plan means steel beams and building control sign-off.
• Kitchen spec. The units and appliances are a project in their own right; see our guide to new kitchen cost in the UK.
• Location. London and the South East typically run 20 to 40% above the national average for the same build.
• Planning. Many rear extensions fall under permitted development, but conservation areas, listed buildings and larger footprints often need full planning permission.

Before you commit, read our explainer on planning permission and building regs for interior projects, and if you are weighing whether to bring in a professional, our honest take on whether an interior designer is worth it covers where the fee pays for itself. For the wider budget picture, see our interior design budget planner.

For the official rules on what you can build without full planning permission, the government’s Planning Portal guidance on extensions is the authoritative source.

Frequently asked questions

How much does a kitchen extension cost in the UK? A single-storey rear kitchen extension typically costs £30,000 to £70,000 across the UK, a side return £35,000 to £60,000, and a wrap-around £60,000 to £100,000. In London, expect roughly 20 to 40% more, with rear extensions commonly £80,000 to £150,000 all in.

Which kitchen extension gives the most space? A wrap-around extension gives the biggest increase in floor area because it combines a rear extension with a filled-in side return in an L-shape. It is also the most expensive and disruptive option, so it suits homeowners who want a large open-plan kitchen, dining and living space.

Do I need planning permission for a kitchen extension? Many single-storey rear extensions fall under permitted development and do not need full planning permission, but limits apply, and conservation areas, listed buildings and larger or wrap-around extensions usually do require it. All extensions must still meet building regulations, so check with your local authority before starting.

How do I get more light into a kitchen extension? Roof glazing is the most effective route: a roof lantern, a run of rooflights or a full glass roof section brings light deep into the new space. Large sliding or Crittall-style doors onto the garden add to this. On narrow side-return extensions a glazed roof is essential to avoid a dark room.

How long does a kitchen extension take to build? A straightforward single-storey rear or side-return extension usually takes around three to four months on site, while a larger wrap-around can run five to six months or more. Design, planning and building control sign-off happen before that and can add several months, so plan the whole project over the best part of a year.