How much does a house extension cost in the UK?

A house extension costs £2,000 to £3,200 per m² in the UK, typically around £2,500. What moves the price most is floor area in square metres and single versus double storey, so a simpler job sits near the bottom of that range and a larger or higher-spec one near the top. Prices reviewed June 2026.

Extensions are priced by floor area, then by finish. A single storey extension is the common project, and the kitchen or bathroom fit-out inside it can add a lot.

To price the whole job, use the extension cost calculator, loft conversion cost calculator, garage conversion cost calculator or conservatory cost calculator.

House extension cost breakdown

House extension costs £2,000 to £3,200 per m² for a standard job, so a 20 m² job comes to about £50,000.

House extension cost by size

Builders price an extension per square metre of floor area, so these totals are this guide's rates multiplied out. A two storey extension counts the footprint twice, at the lower two storey rate.

Build only, at this guide's per m² rates: foundations, structure, roof, windows, doors, basic electrics and plastering. Building control fees, a kitchen, design fees and a party wall surveyor are on top. UK averages, including VAT, not quotes.

Building control fees by council

Most councils set their own building control charges. These are the building notice charges, including VAT, in each council's band for a single-storey extension of about 25 m². Of the 123 councils below, the building notice charge runs from £591 to £1,875.55, and 64 of them charge £924 or less.

From each council's own website, checked October 2026. Bands differ between councils, so the note says where a council's is unusual. A full plans application is usually split into a plan charge and an inspection charge instead. A registered building control approver can be used instead of the council and quotes separately. Most councils set new charges each April.

What's included in the price?

Typical house extension prices include:

• Foundations, structure, roof and shell
• Windows, doors and basic electrics
• Plastering and standard finish
• Work built to pass building control inspection

What changes the price?

The things that move house extension prices most:

How the price is built up

Most builders price an extension on a rate per square metre of floor area, which is why the headline runs from £2,000 to £3,200 per m². The lower end covers a plain single storey shell with a standard finish, while £2,500 per m² is closer to what a real kitchen or living extension costs once you include foundations, a watertight roof, plastering, basic electrics and decoration. You move toward £3,200 per m² with a higher specification and harder structure, such as underfloor heating or large structural openings into the existing house. A fitted kitchen, a bathroom's fittings and bi-fold doors are charged on top of the per m² shell figure, not within it. On a typical extension labour is roughly 55 to 65 per cent of the build cost, with materials and fixed items like windows, doors and the kitchen making up the rest, so a quote that looks cheap on materials but light on labour days is usually under-scoped.

Build a whole-project budget for a 20 m² extension

The base £2,000 to £3,200 per m² rate gives £40,000 to £64,000 for a 20 m² build. Selecting the £10,000 to £25,000 kitchen option gives £50,000 to £89,000 for build plus kitchen. Neither figure is a complete professional-fees or exceptional-groundworks budget.

For a budgeting illustration, a £50,000 build and £15,000 kitchen total £65,000 before separate items. Add the actual quotes for drawings, engineering, building-control fees, any required planning or party-wall work, and specification upgrades. Record temporary accommodation and a contingency separately. An unknown item is still a cost to resolve, not zero.

These guide figures include VAT where applicable. Check each supplier’s VAT wording before comparing quotes and do not add VAT twice. The kitchen option should only be added if that work is outside the builder’s base quote; standard doors and premium glazing also need an explicit boundary.

Ways to keep the cost down

• Keep the kitchen, bathroom and any wet rooms close to existing drainage and the soil stack, because moving them adds plumbing runs and labour for no extra floor space.
• Get the ground checked early, since a sloping plot, trees nearby or made-up ground can force deeper foundations that add several thousand pounds you cannot see in a per m² rate.
• Settle the design, the kitchen layout and the door and window sizes before work starts, as changes once the builder is on site are where budgets quietly run over.
• Get at least three itemised quotes on the same drawings and specification, so you are comparing the same scope rather than a thin number against a complete one.

Does where you live change the cost?

In London, a house extension typically costs around £3,000 per m², about 20% above the UK average of £2,500. In the North, Scotland and Wales the guide figure is nearer £2,400.

Guide prices per m², scaled with the same regional multipliers as the calculator. Not quotes.

House extension cost in major UK cities

City guide estimates, scaled by local labour costs. Indicative averages for house extension, not quotes.

In London and the South East, figures run above the national rate per square metre, on labour, access and waste disposal.

Common questions

Official guidance and sources

The rules and schemes referenced on this page come from these official UK sources. The price figures are Costwise's own; see how we price.

• Planning permission: common projects Planning Portal · Many single-storey extensions are permitted development within size limits; check before you build.
• When you need planning permission GOV.UK · When a home project needs planning permission; building regulations apply either way.

These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.