Kitchen Extension Cost London 2026: The Complete Price Breakdown
A kitchen extension is two projects in one: the build and the kitchen itself. Most guides only quote the build. This guide gives you the all-in cost, broken down by size, spec, and where every pound actually goes.
Quick Answer
A kitchen extension in London costs £60k–£220k+ all-in (inc VAT) depending on size and specification. That is the build cost AND the kitchen combined. A typical 20m² mid-range project runs £100k–£140k total. The build accounts for roughly 60% and the kitchen plus finishes around 40%.
£60k–£110k
Small (15m²)
£85k–£160k
Medium (20m²)
15–25%
Value added
Check your specific property constraints
Free Property CheckWhy Kitchen Extensions Cost More Than You Think
Every kitchen extension is really two overlapping budgets. The first is the building work: foundations, walls, roof, structural opening, glazing, and making it weathertight. The second is everything that turns that empty shell into a working kitchen: the units, worktops, appliances, plumbing, electrical fit-out, flooring, and decoration.
Most cost guides quote only the build. When homeowners then add a kitchen, appliances, underfloor heating, and decoration on top, the final number can be 40–60% higher than the figure they budgeted for. This guide gives you the all-in number from the start.
The two budgets
Foundations, walls, roof, structural steel, glazing, insulation, drainage, electrics first fix
Kitchen units, worktops, appliances, plumbing, flooring, lighting, decoration
All figures inc VAT at 20%. The build cost per m² covers the shell only. Kitchen cost varies enormously by brand, material, and appliance specification.
2026 All-In Costs by Size
These are total project costs including the extension build, professional fees, the kitchen itself, and a 10% contingency. All figures include VAT at 20%.
| Size | Build cost | Kitchen cost | All-in total |
|---|---|---|---|
| Small (12–15m²) | £50k–£90k | £10k–£20k | £60k–£110k |
| Medium (16–24m²) | £70k–£130k | £15k–£30k | £85k–£160k |
| Large (25–36m²) | £100k–£180k | £20k–£40k | £120k–£220k |
The ranges are wide because specification makes a huge difference. A 20m² extension with IKEA units and standard appliances costs roughly £95k all-in. The same 20m² with a bespoke kitchen, Miele appliances, and premium finishes could reach £155k. Same size, same footprint, 60% higher cost.
Build Cost per m² by Spec Level
This is the extension build only, before the kitchen is fitted. Professional fees and contingency add 15–20% on top.
All figures inc VAT at 20%. Smaller extensions cost more per m² due to fixed costs (structural opening, foundations, roofing details). Inner London (zones 1–2) typically runs 10–15% above these figures.
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What the Build Cost Includes vs What Is Extra
A builder's quote for the extension shell typically covers the structural work. Everything that makes it a kitchen is usually a separate budget line. Here is the split.
| Included in build | Usually extra |
|---|---|
| Foundations and ground slab | Kitchen units and worktops |
| External walls and insulation | Appliances (oven, hob, fridge, dishwasher) |
| Flat roof and membrane | Flooring (tiles, engineered wood, polished concrete) |
| Structural steel and opening | Underfloor heating |
| Glazing (bi-folds or sliding doors) | Island plumbing and drainage |
| First-fix electrics and plumbing | Lighting design and pendants |
| Drainage connection | Range cooker gas supply and extraction |
| Plastering and decoration (basic) | Decoration (painting, tiling, splashbacks) |
The items on the right are what turn a builder's £80k quote into a £120k project. Knowing this upfront prevents the budget shock that hits most homeowners around month three.
Kitchen-Specific Costs That Add Up
A kitchen in an extension has specific requirements that a standard kitchen replacement does not. These items are routinely underestimated.
An island with a sink needs drainage run under the slab, which must be planned before the concrete is poured. A range cooker on an island needs both gas supply and ducted extraction through the flat roof. These are not afterthoughts; they are decisions that have to be made during the design stage, not during the build.
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Professional fees add 10–15% to the build cost. These are not optional. A kitchen extension without proper design and engineering invites expensive problems during the build.
Total professional fees for a typical kitchen extension: £8,000–£16,000. Many architects include kitchen layout in their service. If yours does not, budget separately for a kitchen designer.
How to Budget: The 60/40 Rule
A useful rule of thumb for kitchen extensions: roughly 60% of your total budget goes on the build (the extension itself, professional fees, and contingency) and 40% goes on the kitchen, finishes, and fit-out (units, appliances, flooring, lighting, decoration).
Applying the 60/40 rule
£100k total budget
£60k on the build (15–18m² mid-range extension) and £40k on the kitchen and finishes. This buys a solid mid-range result with good units, decent appliances, and engineered wood flooring.
£150k total budget
£90k on the build (20–24m² mid-to-high spec) and £60k on a premium kitchen with high-end appliances. This is where most London homeowners land for a properly generous kitchen-diner.
£200k+ total budget
£120k+ on the build (25–36m² high-spec extension) and £80k+ on a bespoke kitchen, premium appliances, and architect-designed finishes throughout.
The ratio shifts at the extremes. A small extension with a high-end kitchen might split 50/50. A large extension with a budget kitchen might split 70/30. The 60/40 split applies to a typical mid-range project and is a reliable starting point for early-stage budgeting.
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Where Money Gets Wasted
Kitchen extensions have specific budget traps that catch homeowners on nearly every project. Here are the most common.
Over-specifying the build for a basic kitchen
Spending £5,000/m² on the extension shell with bespoke glazing and then fitting a £8,000 kitchen looks wrong and wastes value. The kitchen is what you see and use every day. If your budget is limited, put the money where it matters most: the kitchen and finishes, not the structural specification.
Under-sizing the extension for an expensive kitchen
A £35,000 kitchen crammed into a 12m² extension looks and feels wrong. If the budget only stretches to a small extension, a £15k mid-range kitchen will look better and function better in the space. Match the kitchen to the room, not the other way around.
Deciding the kitchen layout after construction starts
Drainage runs, gas supply, electrical positions, and extraction routing all need to be decided before the slab is poured. Moving a sink position after the ground floor is laid costs £2,000–£5,000. Engage your kitchen designer alongside your architect from the outset.
No contingency in the budget
Kitchen extensions encounter more unknowns than other extension types: existing drainage positions, soil conditions, asbestos in outrigger demolition, and unexpected structural requirements. Budget 10% contingency on the build cost as a minimum. In older London properties, 15% is safer.
Planning Route for Kitchen Extensions
Most kitchen extensions are single-storey rear extensions. The planning route depends on depth, house type, and whether your property is in a conservation area.
| Scenario | Route | Cost |
|---|---|---|
| Up to 3m depth (terraced/semi) | Permitted development | £0 |
| Up to 4m depth (detached) | Permitted development | £0 |
| 3–6m depth (terraced/semi) | Prior approval | £120 |
| 4–8m depth (detached) | Prior approval | £120 |
| Conservation area (any depth) | Full planning | £528 |
| Exceeds PD/prior approval limits | Full planning | £528 |
Most kitchen extensions in London are 3–5m deep and fall within either permitted development or prior approval. A 4m rear extension on a terraced house is the most common kitchen extension project in London and uses the prior approval route. Wrap-around extensions (rear plus side return) follow the same rules but the combined footprint must meet all PD conditions.
Planning permission adds 8–12 weeks to your timeline but does not significantly add to cost beyond the £528 application fee and potentially more detailed architectural drawings.
Timeline: Design to Cooking
Kitchen extensions take longer than other extension types because of the fit-out complexity at the end. Here is the realistic timeline.
Design and drawings
4–6 weeksArchitect design, structural engineer, kitchen layout coordination. The kitchen designer should be involved from this stage.
Planning / prior approval
0–10 weeks0 weeks for PD, 6–8 weeks for prior approval, 8–10 weeks for full planning
Party wall and building regs
2–4 monthsRuns in parallel with planning. Party wall notices should be served as soon as you have outline drawings.
Construction
12–18 weeksFoundation to weathertight shell: 8–10 weeks. Remaining time is second fix, plastering, and kitchen fit-out preparation.
Kitchen installation and finishes
3–5 weeksKitchen fitting, appliance connection, worktop templating and installation, flooring, tiling, and decoration.
Total project
5–9 monthsPermitted development with no party wall: 5–6 months. Prior approval with party wall: 7–8 months. Full planning with party wall: 8–9 months. Add 4–6 weeks if the kitchen units have a long lead time (common with bespoke manufacturers).
Kitchen lead times: Order your kitchen as soon as construction starts. Mid-range kitchens (Howdens, Wren, Magnet) typically deliver in 4–6 weeks. Bespoke manufacturers (Roundhouse, Plain English, DeVOL) can take 8–14 weeks. If you wait until the shell is built to order, you add months to the project.
Value Added: The Best Return on Any Extension
Kitchen extensions consistently deliver the highest return on investment of any home improvement project. A well-designed open-plan kitchen-diner in London typically adds 15–25% to property value. In high-demand boroughs like Wandsworth, Hackney, and Islington, the uplift can exceed the project cost.
Value uplift by property type
Figures based on London estate agent valuations 2025–2026. Actual uplift depends on design quality, kitchen specification, and local market conditions. An open-plan kitchen-diner is the single most requested feature among London buyers.
The reason is simple: a kitchen extension transforms everyday life. It is the room you use most and the room buyers judge most. Every pound spent on a well-designed kitchen-diner is more visible to a buyer than the same pound spent on a loft conversion or basement.
Frequently Asked Questions
How much does a kitchen extension cost in London in 2026?
A kitchen extension in London costs £60k–£220k+ all-in (inc VAT) depending on size and specification. That includes the build AND the kitchen. Small (12–15m²): £60k–£110k. Medium (16–24m²): £85k–£160k. Large (25–36m²): £120k–£220k. Build cost alone is £3,000–£5,500/m², then add £8,000–£40,000+ for the kitchen units, appliances, and finishes.
What is the cost per m² for a kitchen extension in London?
Build cost per m² in London 2026: budget spec £3,000–£3,600/m², mid-range £3,600–£4,500/m², high-spec £4,500–£5,500/m². All figures include VAT. These are construction costs only — add the kitchen (£8,000–£40,000+), professional fees (£8,000–£16,000), and 10% contingency for the all-in figure.
How much should I budget for the kitchen itself?
Budget kitchen (IKEA, Howdens basic range): £8,000–£12,000. Mid-range (Howdens premium, Wren, Magnet): £12,000–£25,000. Bespoke (Roundhouse, Plain English, DeVOL): £25,000–£40,000+. Add £3,000–£6,000 for a mid-range appliance package or £8,000–£20,000+ for premium brands like Miele or Sub-Zero.
Do I need planning permission for a kitchen extension in London?
Most single-storey kitchen extensions qualify for permitted development (no application needed) within 3m depth for terraced/semi-detached or 4m for detached houses. Between 3–6m (terraced/semi) or 4–8m (detached), a prior approval application is needed (£120 fee). Conservation areas and listed buildings need full planning permission (£528 fee).
How long does a kitchen extension take from start to finish?
Total project: 5–9 months. Design: 4–6 weeks. Planning/prior approval: 0–10 weeks. Construction: 12–18 weeks. Kitchen installation and finishes: 3–5 weeks. The party wall process (2–4 months) runs in parallel. Order your kitchen as soon as construction starts to avoid delays — bespoke kitchens can take 8–14 weeks to manufacture.
Does a kitchen extension add value to my London home?
Yes, a kitchen extension is the highest-ROI home improvement in London. A well-designed open-plan kitchen-diner typically adds 15–25% to property value. On a £700,000 London terraced house, that is £105k–£175k of added value against a typical project cost of £100k–£140k. The return depends on design quality and finish level.
What is the 60/40 rule for kitchen extension budgets?
The 60/40 rule is a budgeting guide: roughly 60% of your total budget goes on the extension build (construction, professional fees, contingency) and 40% goes on the kitchen and finishes (units, appliances, flooring, lighting, decoration). On a £120k total budget, that means £72k on the build and £48k on the kitchen. The ratio shifts at extremes.
What hidden costs are there in a kitchen extension?
Common hidden costs: island plumbing and drainage (£1,500–£3,000), gas supply to island (£800–£1,500), extraction ducting (£600–£2,000), underfloor heating (£3,000–£6,000), party wall surveyors (£800–£1,400 per neighbour), and the kitchen itself if not factored in from the start. Always budget 10–15% contingency on top of quoted costs.
Summary
A kitchen extension is the most valuable home improvement you can make in London, but it is also the one most likely to go over budget. The reason is always the same: the kitchen itself was not included in the original budget.
Use the 60/40 rule as your starting framework. Set the total budget first, then work backwards into what size extension and what quality kitchen that affords. Get your kitchen designer involved during the design stage, not after construction. Order the kitchen as soon as the build starts.
A typical 20m² mid-range kitchen extension in London costs £100k–£140k all-in. That buys a properly generous open-plan kitchen-diner that transforms how you live and adds 15–25% to the value of your home. There is no better investment in a London house.
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