Kitchen extension cost by size and fit-out level
Build costs below cover the structure, insulation, underfloor heating rough-in, plastering, and glazed doors. Kitchen fit-out is shown separately. London/South East add 20-30%.
| Size | Build cost (structure only) | Budget kitchen | Mid-range kitchen | High-spec kitchen |
|---|---|---|---|---|
| 10 m2 | £15,000 to £25,000 | +£5,000 to £10,000 | +£10,000 to £18,000 | +£18,000 to £30,000 |
| 15 m2 | £22,500 to £37,500 | +£6,000 to £12,000 | +£12,000 to £20,000 | +£20,000 to £35,000 |
| 20 m2 | £30,000 to £50,000 | +£7,000 to £14,000 | +£14,000 to £22,000 | +£22,000 to £40,000 |
| 25 m2 | £37,500 to £62,500 | +£8,000 to £16,000 | +£16,000 to £25,000 | +£25,000 to £45,000 |
Build costs per m2: basic £1,500, standard £2,000, premium £2,500-£3,000. Fees (architect, structural engineer, building regs) add £3,000-£8,000. VAT at 20% applies to most works.
What affects the cost of a kitchen extension?
The range between cheapest and most expensive kitchen extensions is enormous. These are the key cost drivers:
- Extension type: a simple rear extension is generally cheaper than a side-return extension, which involves working in a confined space, often with party wall implications. Wrap-around extensions combining rear and side-return are the most expensive.
- Size: every extra square metre adds to structural, roofing, flooring, and fit-out costs. Many planning constraints also limit single-storey rear extensions to 4 m (3 m for semi or terraced) under permitted development.
- Glazing specification: bifold or sliding doors (£3,000 to £10,000 for a typical opening) and rooflights add substantial cost but transform the space. Steel-framed Crittal-style glazing is fashionable and expensive.
- Roof type: a flat roof with a rooflight is cheapest. A pitched roof to match the existing house or a glass lantern roof adds cost but can improve resale appeal.
- Kitchen fit-out: this is often the single largest variable. A flat-pack kitchen from a DIY retailer costs £3,000 to £8,000 fitted; a mid-range designer kitchen £12,000 to £22,000; a bespoke handmade kitchen £25,000 to £60,000 or more.
- Structural work: knocking through an existing rear wall to open the extension into the main house requires a steel beam (RSJ), typically £1,500 to £3,500 supply and install, plus structural engineer design fees.
- Underfloor heating: popular in kitchen extensions; wet systems cost £800 to £1,500 to install in a screed, electric systems from £500.
- Location: London and South East labour and material costs run 20-30% above the national average. A £45,000 project in the Midlands may cost £55,000 or more in London.
Rear extension vs side-return extension: which suits your home?
The most common type of kitchen extension for terraced and semi-detached houses is the rear extension, projecting straight back into the garden. Under permitted development, a single-storey rear extension can project up to 4 m from the original rear wall for a detached house or 3 m for a semi-detached or terraced property, without planning permission (subject to prior approval under the neighbour consultation scheme for 4-8 m). Larger extensions need a full planning application.
The side-return extension fills the narrow passage that runs along the side of many Victorian and Edwardian terraced and semi-detached houses. While the additional floor area can be modest (often just 20-30 m2 combined with the existing kitchen footprint), the removal of the external wall and the introduction of glazing transforms these previously dark rooms into light-filled open-plan spaces. Side-return extensions typically cost more per square metre due to confined working conditions and are very common in London, where many older terraced houses have this feature.
A party wall notice is almost always required for a side-return extension that involves work on or close to the shared boundary, and building against the neighbour's wall may require a Party Wall Agreement. Budget £700 to £2,000 for a party wall surveyor if one is needed.
Steps to planning and budgeting your kitchen extension
A kitchen extension involves multiple professionals and a long lead time. Getting the sequence right saves money and stress.
Appoint an architect or designer
A good architect will maximise the space, help navigate planning rules, and produce drawings for planning and building regulations. Expect to pay £2,000 to £6,000 for design and planning services on a typical kitchen extension.
Check permitted development limits and planning requirements
Confirm with your local authority whether the extension falls within permitted development or needs a full planning application. In conservation areas, PD rights are often restricted even for small rear extensions.
Appoint a structural engineer
A structural engineer designs the beam over any new opening, specifies foundations, and produces calculations for building regulations. Fees are typically £500 to £1,500 for a standard residential project.
Serve party wall notices if required
If the extension involves work on or within 3 m of a party wall or shared boundary, you must serve notice on your neighbour at least 2 months before work begins. Allow time for this in your programme.
Get three builders' quotes
Always obtain at least three like-for-like quotes from builders with verifiable references. Be specific about what is included (VAT, groundworks, glazing, connection to heating system, making good internally).
Budget for the kitchen fit-out separately
The kitchen fit-out is usually specified and purchased separately from the main build. Allow enough time for delivery lead times (8-16 weeks for bespoke kitchens) so the kitchen is ready when the building is completed.
Pitfall: underestimating total project costs
Most kitchen extension budgets focus on the build cost and forget several significant additional items: VAT at 20% on most labour and materials; architect and structural engineer fees of £3,000 to £8,000; building regulations fees of £800 to £1,500; party wall surveyor costs of £700 to £2,000 if applicable; and internal making good (decoration, flooring, lighting). A project quoted at £35,000 for the structure can easily reach £50,000 or more once all elements are accounted for. Always build in a 15-20% contingency for unforeseen works.
Add it to your pre-purchase budget
Our planner helps you set a realistic refurbishment reserve before you buy. If you are considering a property specifically to extend the kitchen, model the full cost - build, fit-out, fees, and contingency - before you make an offer so you know your true all-in spend.