Kitchen Extension Cost UK 2026: £15,000-50,000 for a Single-Storey Rear Extension
Quick Answer
A single-storey kitchen extension in the UK costs £15,000-35,000 in 2026, depending on size and specification. At a per-m2 rate, budget £1,500-2,500/m2 for a basic to mid-range finish. A 20m2 extension at mid-range specification costs £30,000-50,000 including all trades but excluding kitchen units and appliances. London adds 30-40%.
What Does a Kitchen Extension Cost in the UK?
A kitchen extension is one of the most popular home improvement projects in the UK, and for good reason. It adds usable living space, improves how the ground floor flows, and typically delivers strong returns on investment when it comes to property value. The challenge for homeowners is that the cost range is genuinely wide: a modest 12m2 lean-to extension at basic specification is a very different project to a 30m2 open-plan rear extension with full-width bi-fold doors, a glazed roof lantern, and underfloor heating.
This guide is written for both homeowners planning a project and tradesmen quoting extension work. For homeowners, it provides a realistic cost framework to budget from before engaging architects or builders. For tradesmen, it offers a useful benchmark for checking that project quotes and labour rates sit within market norms.
The figures here cover the structural build: groundworks, foundations, brickwork, roof, windows and doors (standard), first and second fix electrics and plumbing, plastering, and basic floor prep. They do not include kitchen units, appliances, or bi-fold doors, which are itemised separately below. Architect fees and planning costs are also separate.
The labour component of an extension project typically accounts for 45-55% of the total build cost. For a detailed breakdown of what individual trades charge on extension projects, see our builder day rate guide, which covers current rates for builders handling extension work across the UK in 2026.
Costs have continued to rise in 2026. Materials inflation and sustained demand for domestic building work mean that budgets from 2022 or 2023 are likely to be meaningfully out of date. The figures in this guide reflect current market rates as of mid-2026 and should be used as a realistic planning baseline rather than a ceiling.
Kitchen Extension Cost by Size: 2026 Figures
The table below shows indicative costs for single-storey rear kitchen extensions at basic and mid-range specification. Basic covers standard brickwork, a flat or tiled lean-to roof, standard casement windows, and no underfloor heating. Mid-range covers better materials, a roof lantern or rooflight, and a higher standard of finish throughout. All figures exclude kitchen units, appliances, bi-fold doors, architect fees, and planning. London adds 30-40%.
| Extension Size | Basic Spec | Mid-Range Spec |
|---|---|---|
| Small extension (up to 15m2) | £18,000-25,000 | £25,000-35,000 |
| Medium extension (15-25m2) | £25,000-38,000 | £38,000-55,000 |
| Large extension (25m2+) | £38,000-55,000 | £55,000-80,000+ |
Figures are for single-storey rear extensions on a typical terraced or semi-detached house with standard site conditions. Costs exclude kitchen units, appliances, bi-fold doors, architect fees, and planning permission. London and South East add 30-40%.
What Is Included in These Costs?
The cost ranges above cover the complete structural build from the ground up to a plastered and decorated shell, ready for kitchen fitting and flooring. The following items are included in the quoted figures:
- ✓Groundworks and foundations
- ✓Brickwork and blockwork
- ✓Roof structure
- ✓Rooflight or flat roof
- ✓Electrics and plumbing alterations
- ✓Plastering and decoration
- ✓Flooring (screed or timber substrate, not finish flooring)
- ✓Building regulations sign-off
The structural work alone, covering groundworks, concrete, steels where required, and brickwork, typically accounts for 40-50% of the total build cost. Roof works, glazing, and first and second fix trades make up most of the remainder. Decoration is usually included at a basic standard: one colour throughout, standard plasterboard finish, no feature walls or specialist treatments.
What Is Not Included: Budget Separately for These
Several significant costs sit outside the build contract and need to be budgeted separately. These are often where homeowners underestimate the total project cost.
- ✗Kitchen units and appliances: Budget separately £5,000-30,000 depending on the brand and specification. IKEA or B&Q kitchens sit at the lower end; bespoke or semi-bespoke fitted kitchens from a specialist are at the top.
- ✗Bi-fold or sliding doors: Add £3,000-8,000 per set for aluminium bi-fold doors. uPVC is cheaper but less durable. Larger openings with more panels cost more.
- ✗Architect fees: Typically £1,500-5,000 for drawings and specification. Some projects use a building designer rather than a full architect, which can cost less.
- ✗Planning permission fee: The current householder application fee in England is £206. Many extensions fall under permitted development and do not need a formal application.
When you add kitchen units, bi-fold doors, and architect fees to a mid-range 20m2 extension, the total project cost can easily reach £60,000-80,000. It is worth building a complete project budget from the outset rather than pricing the build alone and adding the other costs later, when they can come as a surprise.
Key Factors That Affect Kitchen Extension Cost
The difference between a £20,000 extension and a £55,000 extension of similar size nearly always comes down to a handful of specific decisions. Here is what drives cost up or down on kitchen extension projects in 2026.
Extension Size in m2
This is the most obvious driver. A larger footprint means more groundworks, more materials, and more labour across every trade. However, there is some economy of scale: the per-m2 rate often falls slightly as size increases, because fixed costs such as scaffold, plant hire, and mobilisation are spread across more square metres. A 25m2 extension is not simply 25% more expensive than a 20m2 extension of the same specification.
Specification Level
Basic specification uses standard brickwork, a flat or corrugated roof, standard casement windows, and functional but unremarkable finishes. Mid-range adds a roof lantern or quality rooflights, better-insulated walls and roof, and a higher standard of plastering and decoration. Premium specification includes full-width glazing, structural glass, feature steels, polished concrete floors, and bespoke joinery. Moving from basic to premium can double the cost per m2.
Glazing Choices
Glazing is the single biggest specification variable after overall size. A small rooflight costs £500-1,500 to supply and fit. A quality roof lantern for a flat roof extension runs £3,000-8,000 installed. A set of aluminium bi-fold doors across a 3-4 metre opening adds £4,000-7,000. Full-width sliding glass walls or structural glass roofs are at the very top of the range. Many homeowners plan for bi-folds at the outset of budgeting but forget to separate this cost from the build contract.
Underfloor Heating
Wet underfloor heating (connected to the boiler) costs £1,500-3,000 to install in a typical kitchen extension, including pipework, manifold, and screed. Electric underfloor heating is cheaper to install (£400-800) but more expensive to run. Underfloor heating is most cost-effective when installed during the build, as it requires laying pipework before the screed goes down. Retrofitting it later is significantly more disruptive and expensive.
Location and Regional Premium
London and the South East add 30-40% to build costs. This reflects higher trade day rates, greater material delivery costs in congested areas, parking and logistics challenges on urban sites, and the higher overheads that tradesmen in those areas carry. A mid-range 20m2 extension that costs £45,000 in the Midlands could cost £60,000-63,000 in London for identical specification.
Planning Permission Requirements
Most small single-storey rear extensions fall under permitted development and do not need a planning application. Extensions that exceed the permitted development limits, or properties in conservation areas or Article 4 direction zones, will need a formal householder application. This adds the planning fee (£206 in England as of 2026), architect time to prepare a planning package, and a waiting period of 8-13 weeks for a decision. In areas where permitted development rights have been removed, even small extensions require permission.
Regional Price Variation
Build costs for extensions vary significantly across the UK. The national average figures in this guide apply to most of England outside London and the South East. Here is how the major regions compare.
| Region | vs. National Average | 20m2 Mid-Range Estimate |
|---|---|---|
| London | +30-40% | £55,000-65,000 |
| South East | +15-20% | £48,000-56,000 |
| South West | +0-10% | £42,000-48,000 |
| Midlands | National average | £40,000-48,000 |
| North West | -5% | £38,000-45,000 |
| Yorkshire | -5% | £38,000-45,000 |
| North East | -10% | £36,000-43,000 |
| Wales | -10% | £36,000-43,000 |
| Scotland | -5-10% | £36,000-45,000 |
Regional estimates based on a 20m2 single-storey rear extension at mid-range specification. Excludes kitchen, bi-fold doors, architect fees, and planning.
It is worth noting that within regions, city versus rural location also matters. Build costs in Manchester or Leeds are higher than in rural Lancashire or the Yorkshire Dales, reflecting higher trade overheads, greater local demand, and access logistics. These regional averages are a starting point rather than a precise local benchmark.
Extension Cost Per m2 in 2026
Per-m2 cost is the most reliable way to compare extension quotes and spot outliers. The figures below apply to single-storey rear extensions in 2026, outside London and the South East. Add 30-40% for London.
- Basic specification: £1,500-2,000/m2. Standard brickwork, flat or lean-to roof, no rooflights, standard windows, functional finishes.
- Mid-range specification: £2,000-2,500/m2. Quality brickwork, roof lantern or rooflights, better insulation, improved finishes, possible underfloor heating.
- Premium specification: £2,500-3,500/m2. Structural glass, full-width bi-folds or sliding walls, polished concrete, bespoke joinery, underfloor heating throughout.
If a quote you receive converts to a per-m2 rate significantly below the basic range, treat that as a warning sign. It can indicate that the builder has not properly priced the structural elements, is planning to value-engineer the specification, or intends to come back with variations during the project. Use our house extension cost calculator to cross-check any quotes you receive against these benchmarks, and the labour cost estimator to check the labour element specifically. You can also use the hourly rate calculator if you are a tradesman reviewing your own rates against project benchmarks.
How to Get Accurate Extension Quotes
Getting meaningful quotes for an extension project requires some preparation on your part. A builder cannot give a reliable fixed price from a verbal description of what you want. Here is how to set yourself up to get quotes you can compare properly.
- Get architectural drawings first. Even a basic set of drawings showing the footprint, height, roof type, and window positions gives builders something concrete to price from. Without drawings, you will receive ballpark estimates rather than firm quotes, and they will not be comparable with each other.
- Get at least three quotes. The spread on extension quotes can be significant, even for the same drawings. Three quotes gives you a sense of the market and makes outliers obvious in both directions. A quote 30% below the others warrants careful scrutiny; one 30% above may reflect a builder who is busy and not particularly eager for the work.
- Ask for an itemised breakdown. A single lump-sum quote tells you nothing useful. Ask each builder to break the cost down by trade and element: groundworks, brickwork, roof, first fix, second fix, and finishes. This lets you compare like with like and spot where quotes differ.
- Clarify what is and is not included. Confirm explicitly whether bi-fold doors, rooflights, underfloor heating, kitchen removal, and waste disposal are in or out of scope. These items are frequently omitted from quotes and then added back as variations during the project.
- Check references and previous work. Ask to see similar extension projects the builder has completed and speak to those clients if possible. Extension work is a significant investment and the quality of the brickwork, roof construction, and finishing will be visible for decades.
Main Contractor or Self-Managing Trades?
On an extension project, you have two main options for procurement. You can appoint a main contractor who takes responsibility for the whole project, including coordinating and paying all the trades. Alternatively, you can manage the trades yourself, appointing a builder for the structural work, then separately appointing an electrician, plumber, plasterer, and decorator.
A main contractor typically charges a 10-15% management premium over the cost of managing trades directly. On a £45,000 project, that is £4,500-6,750. In exchange, you get a single point of accountability, a programme that the contractor manages, and no need to spend your own time coordinating trades or chasing progress.
Self-managing works best if you have project management experience, can take time off work to manage the programme, and are comfortable dealing with problems directly when they arise. For most homeowners, particularly on projects over £30,000, the time and stress saved by using a main contractor is worth more than the premium paid.
Frequently Asked Questions
Do I need planning permission for a kitchen extension?
Many single-storey rear extensions fall under permitted development and do not need planning permission. The limits are: single storey, no higher than 4m at the ridge, no more than half the garden covered, maximum depth of 3m for terraced and semi-detached houses or 4m for detached houses. Extensions beyond these limits need a householder planning application. Properties in conservation areas, areas of outstanding natural beauty, or subject to Article 4 directions may have permitted development rights restricted or removed entirely. Always check with your local planning authority before starting work.
How long does a kitchen extension take to build?
A straightforward single-storey extension takes 10-16 weeks from groundworks to final decoration. The timeline typically breaks down as follows: groundworks and foundations take 2-3 weeks, brickwork and roof structure take 3-4 weeks, windows and doors installation takes roughly 1 week, first fix trades and plastering take 3-4 weeks, and second fix and decoration take 2-3 weeks. Complex extensions with bi-fold walls, roof lanterns, underfloor heating, or unusual rooflines take longer. This timeline assumes a competent main contractor with trades lined up and no significant delays to materials or building control inspections.
What is the cost per m2 for a house extension in the UK in 2026?
Budget £1,500-2,000/m2 for a basic single-storey extension, £2,000-2,500/m2 for a mid-range finish, and £2,500-3,500/m2 for premium specification with high-end glazing, underfloor heating, and quality finishes. London adds 30-40% to these rates. These figures cover structural works, trades, and basic finishes, but exclude kitchen units and appliances. A quote significantly below £1,500/m2 outside London is worth scrutinising carefully, as it may indicate under-pricing that will result in variations or quality compromises during the project.
Should I use a main contractor or manage the trades myself?
Using a main contractor is simpler and means one point of contact for the whole project. The contractor coordinates trades and takes responsibility for the programme. The premium over managing trades yourself is typically 10-15%. Managing trades yourself saves money but requires significant time and project management skill. You will need to source each trade separately, coordinate their schedules, manage the programme yourself, and deal directly with any problems. For extensions over £30,000, most homeowners find a main contractor reduces stress and risk, and the management premium is a reasonable price to pay for that peace of mind.
What is the most expensive part of a kitchen extension?
The structure (groundworks, brickwork, roof, steels) accounts for roughly 40-50% of the build budget. Glazing is the other major variable: a single set of bi-fold doors costs £3,000-8,000 to supply and install, and a large glazed roof extension can cost £10,000-20,000 just for the glass and frames. The kitchen itself is a separate budget, often matching or exceeding the build cost at mid to premium specification. Adding bi-folds, a roof lantern, and underfloor heating to a project can add £10,000-20,000 to the build cost alone before the kitchen units are considered.
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