Kitchen Extension Cost Guide 2026 — What to Expect & How to Quote

Kitchen extensions are one of the most popular home improvement projects in the UK. For homeowners, they add living space and property value. For builders, they represent significant, profitable projects — but only if you price them correctly. Underquote and you will lose money on a job that takes months. Overquote and you will lose the work entirely.

This guide breaks down what kitchen extensions cost in 2026, what drives those costs, and how to build an accurate quote that protects your margins while remaining competitive. Whether you are a builder quoting your first extension or looking to refine your estimating, the numbers and methods here will help.

Average Kitchen Extension Costs in 2026

Kitchen extension costs vary enormously depending on size, specification, and location. Here are the typical ranges you can expect in 2026.

Single Storey Rear Extension

This is the most common type of kitchen extension — extending the back of the house to create a larger kitchen or open-plan kitchen-diner.

• Small (fifteen square metres): twenty-five thousand to forty thousand pounds
• Medium (twenty to twenty-five square metres): thirty-five thousand to fifty-five thousand pounds
• Large (thirty to forty square metres): fifty thousand to seventy-five thousand pounds

These figures include the building work, first and second fix, plastering, and basic decoration. They do not include the kitchen units, appliances, or any specialist finishes like underfloor heating or bespoke joinery.

Double Storey Extension

Adding a second storey above a kitchen extension is often more cost-effective per square metre because you are sharing the foundation and roof costs. However, the total project cost is obviously higher.

• Small double storey (fifteen square metres per floor): forty thousand to sixty thousand pounds
• Medium double storey (twenty to twenty-five square metres per floor): fifty-five thousand to eighty thousand pounds
• Large double storey (thirty square metres per floor): seventy thousand to one hundred and ten thousand pounds

Wrap-Around Extension

Wrap-around extensions combine a rear and side extension into one L-shaped or U-shaped build. These are popular on semi-detached and detached properties where there is space at the side.

• Typical wrap-around (thirty to forty-five square metres): fifty thousand to ninety thousand pounds

Wrap-arounds tend to cost more per square metre because of the additional external walls and the complexity of the roof junction where the two parts meet.

Full Cost Breakdown

Understanding where the money goes helps you price accurately and explain costs to customers. Here is a typical breakdown for a medium-sized single storey kitchen extension of around twenty square metres.

Foundations

Strip foundations for a standard single storey extension typically cost three thousand to six thousand pounds including excavation, concrete, and blockwork below damp proof course. If the ground conditions require deeper foundations, piling, or underpinning of existing structures, this figure can double. Always recommend a trial hole or ground survey for larger projects to avoid nasty surprises.

Walls and Structural Work

External walls in cavity blockwork with insulation and facing brick typically cost five thousand to ten thousand pounds for a twenty square metre extension. This includes the brickwork, lintels, cavity closers, DPC, and wall ties. If the extension involves removing an existing external wall to open up into the house, the structural steel and associated building work will add one thousand five hundred to four thousand pounds depending on the span.

Roof

A flat roof (the most common choice for single storey rear extensions) costs two thousand to four thousand pounds for materials and labour. A pitched roof adds two thousand to five thousand pounds more but offers a more traditional appearance and typically a longer lifespan. Rooflights or skylights add three hundred to one thousand two hundred pounds per unit depending on size and specification.

Windows and Doors

Bi-fold or sliding doors are the popular choice for kitchen extensions, connecting the kitchen to the garden. A three-panel aluminium bi-fold door costs two thousand five hundred to five thousand pounds supplied and fitted. Roof lanterns — a popular feature in kitchen extensions — range from one thousand five hundred to four thousand pounds depending on size.

Plumbing

First and second fix plumbing for a kitchen extension typically costs one thousand five hundred to three thousand pounds. This includes relocating or extending water supply and waste pipes, connecting the kitchen sink, dishwasher, and potentially a boiler relocation. If the boiler needs moving, add one thousand to two thousand pounds.

Electrics

First and second fix electrics for a kitchen extension cost one thousand five hundred to three thousand five hundred pounds. This covers new circuits for sockets, cooker supply, lighting (including under-cabinet and feature lighting), extractor fan wiring, and any outdoor lighting. Underfloor heating electrics add five hundred to one thousand five hundred pounds.

Plastering and Internal Finishes

Plastering the new space costs one thousand to two thousand five hundred pounds. Flooring varies hugely — budget for one thousand to three thousand pounds depending on the material (vinyl, tile, engineered wood, or polished concrete). Decorating adds five hundred to one thousand five hundred pounds.

Kitchen Fitting

The kitchen itself is a separate cost from the building work. A mid-range kitchen with worktops, units, sink, and tap costs five thousand to fifteen thousand pounds supplied and fitted. High-end kitchens with stone worktops, handleless units, and premium appliances can reach twenty-five thousand pounds or more.

Factors Affecting Kitchen Extension Costs

No two extensions cost the same. Here are the factors that cause the biggest price variations.

Location. Building costs vary significantly across the UK. London and the South East are the most expensive, typically twenty to thirty per cent above the national average. The Midlands sits roughly at the national average, while the North of England, Wales, and Scotland tend to be ten to twenty per cent below. Labour rates are the main driver of these regional differences.

Ground conditions. Rocky ground, high water table, tree roots, clay soil, or existing drains in the path of the extension can all increase foundation costs significantly. A ground survey before quoting is essential for larger extensions.

Access. If materials cannot be delivered directly to the build area and need to be barrowed through the house or over neighbouring land, labour costs increase. Limited access also makes skip placement, scaffolding, and crane hire more difficult and expensive.

Specification. The difference between a basic extension and a high-spec one is enormous. Aluminium bi-fold doors cost double uPVC windows. Underfloor heating adds to plumbing and electrical costs. Stone worktops versus laminate, polished concrete floors versus vinyl — every upgrade compounds.

Party wall implications. If the extension is built up to or near a boundary with an adjoining property, the Party Wall Act 1996 applies. The homeowner needs to serve notice on their neighbour, and if the neighbour appoints a surveyor, the fees can run to one thousand to three thousand pounds. While this is the homeowner's cost rather than yours, it affects the overall budget and can delay the project start.

Planning and Building Regulations. Planning application fees are currently two hundred and fifty-eight pounds for a householder application in England. Building Regulations fees vary by local authority but typically range from five hundred to one thousand two hundred pounds. Structural engineer fees for the steel beam calculations add four hundred to eight hundred pounds.

How to Quote a Kitchen Extension Accurately

Getting your extension quotes right is critical. Here is a practical approach that works.

Start with a thorough survey. Visit the property, take measurements, check access, look at the existing structure, and understand what the customer wants. Ask about their budget — it helps you tailor the specification to what they can afford rather than spending hours pricing a job they cannot pay for.

Break the job into trades. Price each element separately — groundwork, brickwork, roofing, plumbing, electrics, plastering, joinery, kitchen fitting, decoration. This ensures you do not miss anything and makes it easy to adjust if the customer wants to change the specification.

Get subcontractor quotes. If you are using subcontractors for specialist work (plumbing, electrics, roofing), get their quotes before you finalise yours. Do not guess their prices — assumptions are where margins get eroded.

Price materials accurately. Get actual prices from your suppliers for the key materials — bricks, blocks, steel, timber, concrete. Do not rely on prices from your last job, as material costs can change significantly between projects. For more on this, see our guide on how to price materials and markup.

Add contingency. Extension projects almost always throw up surprises — unexpected drainage, structural issues discovered during demolition, material delays. Add ten to fifteen per cent contingency on the total. This is not extra profit — it is a realistic allowance for the unknowns.

Present it professionally. An extension quote is a significant document — the customer is spending tens of thousands of pounds. A text message price or a hastily typed email will not cut it. Use a professional proposal format with a clear scope, itemised pricing, timeline, and terms. QuoteSmith generates these automatically from your input, producing a branded PDF that instils confidence and helps you win more work.

Regional Price Differences

Here is a rough guide to how extension costs vary across the UK in 2026, using a medium single storey kitchen extension as the benchmark.

• London: fifty thousand to seventy-five thousand pounds
• South East England: forty-five thousand to sixty-five thousand pounds
• South West England: thirty-eight thousand to fifty-five thousand pounds
• Midlands: thirty-five thousand to fifty thousand pounds
• North West England: thirty thousand to forty-eight thousand pounds
• North East England: twenty-eight thousand to forty-five thousand pounds
• Wales: twenty-eight thousand to forty-five thousand pounds
• Scotland: thirty thousand to forty-eight thousand pounds

These ranges assume a standard specification. High-end projects in any region can exceed these figures significantly.

Frequently Asked Questions

How much does a kitchen extension cost in the UK in 2026?

A single storey kitchen extension in the UK typically costs between thirty thousand and sixty thousand pounds in 2026, depending on size, specification, and location. A small rear extension of around fifteen square metres starts from around twenty-five thousand pounds, while a large open-plan kitchen-diner extension can reach seventy-five thousand pounds or more. London and the South East tend to be twenty to thirty per cent more expensive than the national average.

How long does a kitchen extension take to build?

A typical single storey kitchen extension takes between ten and sixteen weeks from breaking ground to completion. This includes foundations, brickwork, roofing, first fix plumbing and electrics, plastering, second fix, kitchen fitting, and decorating. Weather, supply delays, and the complexity of the design can all affect the timeline. Allow additional time for planning permission if required and always build in a buffer when communicating timelines to customers.

Do I need planning permission for a kitchen extension?

Many single storey rear extensions fall under permitted development rights, meaning you do not need full planning permission. However, there are limits on size, height, and proximity to boundaries. The maximum depth for a single storey rear extension is typically three metres for attached houses and four metres for detached houses, though this can be extended to six or eight metres under the larger home extension scheme with prior approval. You will always need Building Regulations approval regardless of planning permission status.

What is the cost per square metre for a kitchen extension?

In 2026, the average cost per square metre for a kitchen extension in the UK ranges from one thousand five hundred to two thousand five hundred pounds for the building work alone, excluding the kitchen units and appliances. In London and the South East, this rises to two thousand to three thousand pounds per square metre. High-specification finishes, structural glazing, or complex designs can push costs to three thousand five hundred pounds per square metre or beyond.