A kitchen extension is the single most popular type of home extension in the UK. It creates the open-plan kitchen-diner that tops every property buyer's wish list, adds significant value to your home, and transforms the way a family uses its living space. But it is also a significant financial commitment, and the costs can vary wildly depending on size, specification, and location.
This guide covers the real costs of building a kitchen extension in the UK in 2026, from a modest 15 square metre single storey rear extension to a large wrap-around or side return project. Whether you are a homeowner budgeting for your project or a builder quoting extension work, these figures reflect current market rates.
Kitchen Extension Cost Summary
The cost of a kitchen extension is most usefully expressed per square metre, as this allows you to scale the estimate to your specific project size. These figures cover the building work only — foundations, walls, roof, windows, doors, electrics, plumbing, plastering, and decoration. They do not include the kitchen units, appliances, or flooring.
| Extension Type | Cost per m² | Typical Total Cost |
|---|---|---|
| Single Storey Rear (basic spec) | £1,200 – £1,600/m² | £24,000 – £48,000 |
| Single Storey Rear (mid-range) | £1,600 – £2,000/m² | £32,000 – £60,000 |
| Side Return | £1,500 – £2,200/m² | £25,000 – £50,000 |
| Wrap-Around | £1,600 – £2,200/m² | £40,000 – £75,000 |
| London / South East Premium | £1,800 – £2,500/m² | £36,000 – £85,000+ |
The total cost column assumes a typical extension size of 15 to 30 square metres. Add £8,000 to £25,000 for a mid-range kitchen with units and appliances on top of these figures.
Single Storey Rear Extension: £1,200 – £2,000/m²
A single storey rear extension is the most straightforward type of kitchen extension. It extends directly from the back of the house, typically creating a larger kitchen, a kitchen-diner, or an open-plan kitchen-living space. The rear wall of the existing house is either removed entirely (with a steel beam to support the structure above) or partially opened up.
Typical cost breakdown for a 20m² mid-range rear extension (£36,000 to £40,000):
- Foundations (strip or trench fill): £3,000 – £5,000
- Groundwork and drainage: £2,000 – £4,000
- Walls (blockwork, insulation, internal skin): £4,000 – £6,000
- Roof structure (flat or pitched): £3,000 – £5,000
- Windows and bi-fold/sliding doors: £3,000 – £8,000
- Steel beam (to open up rear wall): £1,500 – £3,000
- Electrics (first and second fix): £2,000 – £3,500
- Plumbing: £1,500 – £3,000
- Plastering: £1,500 – £2,500
- Decoration: £1,000 – £2,000
The biggest variable is usually the glazing — bi-fold doors or large sliding glass panels can range from £3,000 for a basic aluminium set to £10,000 or more for premium slim-frame systems.
Side Return Extension: £1,500 – £2,200/m²
A side return extension fills in the narrow alleyway (the "side return") that runs along the side of many Victorian and Edwardian terraced houses. Although the area gained is relatively small (typically 5 to 10 square metres), the impact on the kitchen is dramatic because it transforms a narrow galley kitchen into a much wider space with room for an island or dining area.
Side return extensions cost more per square metre than standard rear extensions because the foundations and roof structure are disproportionately expensive relative to the floor area gained. The structural work to open up the side wall and support the existing building also adds cost.
Common features of a side return extension:
- Glass roof or rooflight to flood the space with natural light
- Structural opening in the side wall with steel beam
- Connection to existing kitchen and dining areas
- Typical size: 5 to 12 square metres
- Often combined with a rear extension for maximum impact
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A wrap-around extension combines a rear extension with a side return or side extension, creating an L-shaped addition that wraps around the corner of the house. This is the most transformative option, producing the largest amount of new floor space and often creating a true open-plan kitchen, dining, and living area.
Wrap-around extensions are more complex structurally because they involve two external walls of the existing building and typically require significant steelwork to support the floors above. They also require more extensive foundations and drainage modifications.
Typical cost for a 25 to 35m² wrap-around extension: £40,000 to £75,000 for the building work, depending on specification and location.
Planning Permission and Building Regulations
Permitted Development
Many single storey rear extensions fall under permitted development rights (PDR) and do not require a planning application. Under current rules in England (2026), you can extend:
- Up to 3 metres from the rear wall (semi-detached or terraced)
- Up to 4 metres from the rear wall (detached)
- Maximum height of 4 metres
- No more than half the garden area covered by extensions
Larger extensions of up to 6 metres (semi-detached or terraced) or 8 metres (detached) may be possible under the prior approval (also called "larger home extension") process. This requires a notification to the council and consultation with neighbours, but is not a full planning application. The fee is currently £120.
Full Planning Permission
If your extension exceeds permitted development limits, or if you live in a conservation area, you will need full planning permission. The application fee is currently £258 in England. You will need architectural drawings, a site plan, and often a design and access statement. The process typically takes 8 weeks.
Building Regulations
Building regulations approval is required for all kitchen extensions, regardless of planning permission. This covers structural stability, fire safety, insulation standards, drainage, and ventilation. Building control fees are typically £500 to £1,000 depending on the size of the extension.
Party Wall Agreement
If your extension is built on or near the boundary with a neighbouring property, you will need to serve a party wall notice under the Party Wall etc. Act 1996. If your neighbours agree without dispute, the cost is minimal. If a surveyor is required, budget £700 to £1,500 per neighbour. For terraced properties, this may involve both neighbours.
Professional Fees
In addition to the building costs, there are several professional fees to budget for.
| Professional | Typical Cost |
|---|---|
| Architect / Designer (drawings and specification) | £2,000 – £5,000 |
| Structural Engineer (calculations and beam design) | £500 – £1,500 |
| Planning Application (if required) | £258 |
| Building Control | £500 – £1,000 |
| Party Wall Surveyor (if required) | £700 – £1,500 per neighbour |
These professional fees typically add £3,000 to £8,000 to the total project cost. They are often overlooked when homeowners are budgeting, so if you are a builder presenting a quote, it is helpful to remind customers of these additional costs. Our material cost estimator can help you build accurate material schedules for extension projects.
The Kitchen Itself
The building work is only half the story. You also need to budget for the kitchen units, worktops, appliances, and flooring. Here are typical costs for kitchen fitting in a new extension.
| Kitchen Specification | Typical Cost (supply and fit) |
|---|---|
| Budget (flat-pack, laminate worktops) | £5,000 – £8,000 |
| Mid-Range (rigid cabinets, quartz worktops) | £10,000 – £18,000 |
| Premium (bespoke, stone worktops) | £20,000 – £40,000+ |
For kitchen fitters quoting this work, presenting the kitchen as a separate section of the proposal makes it easier for the customer to understand what they are paying for the structure versus the fit-out.
Typical Timeline for a Kitchen Extension
Weeks 1 to 3: Foundations dug, concrete poured, drainage laid. This is weather-dependent and delays at this stage are common in winter.
Weeks 4 to 6: Walls built (blockwork), damp proof course, wall ties, and lintels installed.
Weeks 7 to 8: Roof structure built, weatherproofed, windows and doors fitted.
Weeks 9 to 10: Internal wall removed (steel beam installed), first fix electrics and plumbing.
Weeks 11 to 12: Insulation, plasterboarding, plastering.
Weeks 13 to 14: Second fix electrics, flooring, decoration.
Weeks 15 to 16: Kitchen fitting, final connections, snagging, and building control sign-off.
Add 8 to 12 weeks before construction begins for design, planning applications (if needed), building regulations submission, and party wall agreements. The total process from initial design to moving into the new space is typically 6 to 9 months.
Frequently Asked Questions
How much does a kitchen extension cost per square metre in the UK?
A single storey kitchen extension in the UK costs between £1,200 and £2,000 per square metre for the building work in 2026. This includes foundations, walls, roof, windows, doors, plastering, electrics, and plumbing but excludes the kitchen units and appliances. In London and the South East the cost is typically £1,800 to £2,500 per square metre.
Do I need planning permission for a kitchen extension?
Many single storey rear kitchen extensions fall under permitted development and do not require planning permission. Under current rules, you can extend up to 3 metres from the rear wall of a semi-detached or terraced house, or up to 4 metres from a detached house, without planning permission, provided the extension is single storey and does not exceed 4 metres in height. Building regulations approval is always required.
How long does a kitchen extension take to build?
A standard single storey kitchen extension takes 10 to 16 weeks to build from breaking ground to completion. Allow additional time for planning and building control applications before work starts. The total process from initial design to completion is typically 6 to 9 months.
Does a kitchen extension add value to a house?
A well-designed kitchen extension typically adds 5 to 10 percent to the value of a property. For a property worth £350,000, that equates to £17,500 to £35,000 of added value. The return on investment is highest when the extension creates an open-plan kitchen-diner.