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What changes the cost of a kitchen extension?
The cost of a kitchen extension depends on its size and shape, the foundations and ground, the roof and glazing, any steel beams to open up the house, and the new kitchen inside it. This page does not print a price, because we could not find two dated public sources that agree on one.
Last reviewed:What a kitchen extension involves
A kitchen extension adds floor space, usually at the back or side of a house, to make room for a bigger kitchen, often with dining or living space alongside. It is a building project first and a kitchen project second. The builder digs and pours foundations, builds walls and a roof, fits windows and doors, connects drainage, heating and electrics, and then the kitchen goes in.
QuoteZila is starting in Cheshire, with Crewe, Nantwich and Sandbach among the first towns, and anyone in the UK can post a job. We have not put a price on this page. The figures we found for extensions were from builders, lenders and other sites we cannot link to as dated public sources, and they did not agree. This guide covers what moves the price and how to read a quote.
The stages of a kitchen extension
Each stage brings its own costs, and some come before any builder starts:
- Design. Drawings by an architect, designer or technician, and often a structural engineer's calculations for beams and foundations.
- Permissions. Checking planning, applying for building regulations approval and dealing with party wall matters.
- Groundwork. Clearing the site, digging foundations, moving drains and laying the floor slab.
- Shell. Walls, roof, windows, doors and any roof lights.
- Opening up. Removing part of the existing back wall and fitting steel beams.
- First fix. Plumbing, heating, electrics and any gas, before plastering.
- Finishing. Plastering, flooring, the kitchen, second fix and decorating.
Ask each builder which of these stages their quote includes. Some price only the shell and leave the kitchen and finishes to you.
What changes the price of a kitchen extension
| What changes | Why it matters | What to ask |
|---|---|---|
| Size and shape | A larger or more complex footprint means more of everything | What floor area is the price based on? |
| Foundations and ground | Clay, trees, poor ground or nearby drains can mean deeper foundations | Have you allowed for ground conditions, and what if they are worse? |
| Drains | Extensions often sit over or near drains that need moving or protecting | Are drainage works included? |
| Roof type | Flat, pitched and lean-to roofs differ in structure and finish | Which roof, which covering, and what insulation? |
| Glazing | Bifold or sliding doors and roof lights add cost and structure | Which doors and roof lights, and who supplies them? |
| Steel beams | Opening into the house needs engineered beams and temporary support | Is the structural engineer's design included? |
| Heating | Radiators, underfloor heating or a new boiler change the job | How will the new space be heated? |
| Electrics and lighting | New circuits and lighting need a registered electrician | Who does the electrics, and what certificate will I get? |
| The kitchen itself | Units, worktops and appliances are a separate cost | Is the kitchen in this price or separate? |
| Professional fees | Drawings, calculations, applications and party wall costs | Which fees are included, and which are mine? |
| Access | Narrow side access slows deliveries and skips | How will materials and waste get in and out? |
| VAT | Register if taxable turnover for the last 12 months goes over £90,000 [S6] | Does the total include VAT? |
If one quote is well below the others, check whether it includes drainage, the steel and engineer, the glazing, heating and electrics, and the kitchen. These are the lines most often missing.
Planning permission
Many single-storey rear extensions do not need a planning application. The Planning Portal says a single-storey rear extension can be permitted development if it extends no more than four metres beyond the original rear wall of a detached house, or three metres for any other house, and is no more than four metres high [S1]. It says there are further conditions, and that permitted development rules differ on designated land such as conservation areas [S1].
Side extensions, wrap-around extensions and anything on a listed building or in a protected area are more likely to need permission. Councils can also remove permitted development rights in some areas. If you are not sure, ask the council, or ask your designer to apply for a certificate confirming the work is lawful.
Building regulations and structure
Unlike planning, building regulations almost always apply to an extension. GOV.UK says the building regulations cover the construction and extension of buildings, that approval is separate from planning permission and that you might need both [S4].
Building control looks at foundations, structure, fire safety, insulation, ventilation, drainage and electrics. Steel beams and any change to load-bearing walls need a structural engineer's design. Ask your builder who will apply for building regulations approval and who arranges the inspections. Keep the completion certificate safe, because you will need it if you sell.
GOV.UK: find your local council for building control. QuoteZila is not affiliated with this organisation.
This page gives no steps for structural work. Removing or altering a load-bearing wall must be designed by an engineer and carried out by a competent builder under building control.
Party walls and neighbours
If you live in a semi-detached or terraced house, or the extension is close to your neighbour's house, the Party Wall etc. Act 1996 may apply. GOV.UK's guidance on the Act explains that it covers work to an existing party wall, and that it is separate from planning permission and building regulations [S2]. GOV.UK's explanatory booklet says the Act also covers excavation within 3 or 6 metres of a neighbouring building or structure, depending on the depth of the hole or the proposed foundations [S3].
Where the Act applies, you serve a party wall notice on your neighbour before work starts. It is worth talking to them early. Party wall surveyors' fees can add to the cost if a neighbour does not agree to the work, so ask your designer to flag this at the start.
Living with the work
An extension can mean weeks or months of disruption. Ask each builder:
- how long the job will take, and in what order
- when the back of the house will be opened up, and how it will be kept weatherproof and secure
- when you will be without a kitchen, and whether a temporary sink or cooker can be set up
- where skips, deliveries and the welfare facilities will go
- how dust and noise will be managed, and what hours they work
A builder who has thought through the sequence is easier to work with, and a clear programme helps you plan the kitchen delivery and fitting.
How to compare kitchen extension quotes
Citizens Advice says a quote is a fixed price, while an estimate is only a guess [S5]. It suggests written quotes from at least three traders, and that where a deposit cannot be avoided, it should be as low as possible and no more than 25% [S5]. For an extension, ask each quote to state:
- The drawings and specification it is based on.
- Groundwork, foundations and drainage, and how unknown ground will be priced.
- The roof, insulation, windows, doors and roof lights.
- Steel beams, temporary support and the engineer's design.
- Heating, plumbing, electrics and any gas work, with the registered trades named.
- Plastering, flooring and decorating.
- The kitchen, or confirmation that it is excluded.
- Building control, party wall and other fees, and who pays them.
- Stage payments, the start date and the programme.
- Whether VAT is included. A business must register for VAT when its taxable turnover goes over £90,000 [S6].
Agree in writing how changes and extras will be priced once the work starts.
Jobs you might post
These are examples, not taken from real job posts.
- "Semi-detached house. Want a single-storey rear kitchen extension with roof lights and bifold doors, opening into the existing kitchen."
- "Have drawings and building regulations approval for a side return kitchen extension. Looking for builders to quote."
- "Small lean-to extension to make the kitchen bigger. Need a builder who can also arrange the drawings."
Say whether you have drawings or approvals already, the rough size, the roof and doors you want, and whether the kitchen is part of the job.
Get quotes for a kitchen extension
Describe the project and your postcode. Up to five matched local businesses can send you a quote [QZ2]. QuoteZila is free for customers and local businesses [QZ1].
Honest status: QuoteZila is new. We're starting in Cheshire, beginning with Crewe, Nantwich and Sandbach, and growing area by area. Anyone in the UK can still post a job or register a business. How fast you get quotes depends on how many local businesses have joined near you. Businesses can register and receive jobs straight away. We don't check insurance, qualifications or registrations, so please check these yourself before you hire.
Posting a job is not open yet
See our builders, kitchen fitters, electricians and plumbers pages. For the kitchen itself, see what changes the cost of a new kitchen. The roof repair cost guide explains how roofing work is priced.
Questions about kitchen extension prices
How much does a kitchen extension cost?
This page does not print a figure. The size, foundations, roof type, glazing, steel beams, drainage, heating, electrics and the kitchen itself all change the total. Ask builders to price the same drawings and specification, with the kitchen priced separately, so the quotes can be compared.
Do I need planning permission for a kitchen extension?
Not always. The Planning Portal says a single-storey rear extension may be permitted development if it extends no more than four metres beyond the original rear wall of a detached house, or three metres for other houses, and is no more than four metres high. Other conditions apply, so check before you start.
Does a kitchen extension need building regulations approval?
Yes, almost always. GOV.UK says the building regulations cover the construction and extension of buildings, that approval is different from planning permission, and that you might need both. Your builder or designer will usually apply to building control or an approved inspector.
Do I need a party wall agreement?
You may if the work affects a shared wall or involves digging near your neighbour's building. GOV.UK's guidance says the Party Wall etc. Act 1996 is separate from planning permission and building regulations. Read the guidance and talk to your neighbours early.
Is it worth knocking through to the existing kitchen?
Many extensions open into the existing kitchen or dining room, which usually means removing part of a wall and fitting a steel beam. That needs a structural engineer's design and building control approval. It adds cost, but it is often what makes the new space work.
How big a deposit should I pay?
Citizens Advice suggests keeping any deposit as low as possible and no more than 25% of the price where a deposit cannot be avoided. For a larger job, agree stage payments linked to finished work, such as foundations, roof and first fix.
Does QuoteZila check the businesses?
No. We don't check insurance, qualifications or registrations, so please check these yourself before you hire. You can report a quote or a business from your job page.
This page is general information, not professional or legal advice. QuoteZila does not check Gas Safe, WaterSafe, NFRC, NICEIC or other registrations against the register on your behalf: look them up yourself.
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- Loft Boarding: What Changes the Job. Loft boarding in Cheshire sits on joists that may not have been designed for storage. This guide prints no price. It says when building regulations can apply.
- Loft Conversion Cost in Cheshire: What to Ask. Cheshire loft conversion quotes turn on roof shape, stairs and structure. Ask how the roof and the stair sit against the planning limits.
Sources
- QZ1: QuoteZila product fact. QuoteZila home and jobs-for-tradesmen copy.
- QZ2: QuoteZila product fact. QuoteZila FAQ and app README.
- S1: Extensions: planning permission, Planning Portal. Accessed 2026-10-25. https://www.planningportal.co.uk/permission/common-projects/extensions/planning-permission/
- S2: Party Wall etc. Act 1996: guidance, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/guidance/party-wall-etc-act-1996-guidance
- S3: The Party Wall etc Act 1996: explanatory booklet, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/government/publications/preventing-and-resolving-disputes-in-relation-to-party-walls/the-party-wall-etc-act-1996-explanatory-booklet
- S4: Building regulations approval, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/building-regulations-approval
- S5: Before you get work done on your home, Citizens Advice. Accessed 2026-10-25. https://www.citizensadvice.org.uk/consumer/getting-home-improvements-done/before-you-get-building-work-done/
- S6: Register for VAT, GOV.UK. Accessed 2026-10-25. https://www.gov.uk/register-for-vat