Kitchen Extension Cost UK 2026: What to Really Budget For

Here is the question I asked before my kitchen extension started, and the answer I couldn't find: what does a kitchen extension actually cost?

Not the builder's quote. Not the per-square-metre figure from a magazine article. The actual, all-in, nothing-left-out total you need to have available in your bank account.

My extension finished in January 2024. The builder's original quote was £45,500. The final all-in cost was £120,480. The gap between those two numbers — £75,000 — is what this guide exists to explain.

The Short Answer

A single-storey rear kitchen extension in England typically costs:

• £1,100–£1,500 per m² for the builder's structural work alone
• £1,800–£3,500 per m² for everything, all-in
• £45,000–£87,500 total for a typical 25m² extension (fully kitted out)
• £72,000–£140,000 total for a 40m² extension (fully kitted out)

The reason these ranges are so wide is that the "everything" figure depends on your choices — whether you want bifold doors or a standard French door, a stone worktop or laminate, a premium boiler or a basic boiler.

My build: 55m² of new space, completed over 35 months, total cost £120,480. That works out at roughly £2,190 per m² all-in — which sits in the upper half of the typical range, largely because of bifold doors, premium tiling, and an unusually complicated steelwork saga.

Why the Builder's Quote Is Only Half the Story

When a builder quotes for a kitchen extension, they're pricing what they directly build: the foundations, walls, roof structure, and basic fit-out. They are not pricing:

• Architect's drawings
• Planning and building control fees
• Steelwork (often a provisional sum or separate quote)
• Windows and doors (often quoted separately or excluded entirely)
• Utility meter moves (a separate job with your energy supplier)
• Electrics (a separate trade)
• Plumbing (a separate trade)
• Screed (often a provisional sum)
• Plastering (sometimes included, sometimes not)
• Kitchen units and worktops
• Kitchen fitting labour
• Tiling
• Flooring
• Decoration
• Garden reinstatement
• Waste disposal

Every item on that list is real money. When I totted up all the invoices at the end of my build, the builder's work accounted for roughly £45,000 of a £120,000 total. The other £75,000 was made up entirely of the categories above.

Full Cost Breakdown: Category by Category

Here is what each category cost on my build, alongside the 2026 UK market range.

1. Professional Fees (Architect, Planning, Building Control)

You cannot start building without drawings, and you cannot submit drawings without fees.

Architect or architectural technologist: A full package for a single-storey extension — outline drawings, detailed plans, building control documents, and submission — costs £1,500–£2,500. My architect's fees totalled £1,905 for the core work, plus £655 in design modification fees when the steelwork design changed.

Planning application fee (England 2026): £548 for a householder application. (This was £231 when I applied in 2021 — fees have more than doubled since then.) If your extension falls under permitted development rights, you can skip planning permission — but many homeowners apply for a lawful development certificate for certainty. That costs £274 in England (half the planning fee).

Building control full plans application: £250–£550 depending on your local authority and the size of the extension. I paid £882 for a 55.5m² extension.

Party wall: If your extension is within 3 metres of a neighbouring property's wall, you need to serve a party wall notice. If your neighbour consents, there is no cost. If they appoint a party wall surveyor, expect £700–£1,500 per neighbour.

Thames Water (or your water company) build-over agreement: If you're building over or near a public sewer, you need a build-over agreement. I paid £299.

Total professional fees and council charges: £3,000–£6,000 for a typical project.

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2. Builder's Structural Work

This is what the headline quote covers: digging foundations, building walls, erecting the roof structure, making the existing house weathertight, and knocking through the opening.

For a typical single-storey rear extension:

• Foundations: £200–£350 per m² of floor area (normal ground conditions)
• Walls: £7,000–£14,000 total (cavity blockwork to wall plate height)
• Roof structure: £4,000–£7,000 (including insulation, excluding covering)
• Roof covering: £2,500–£4,500 for a typical 25–30m² extension
• Scaffolding: £1,200–£2,500

Total builder's structural work: £25,000–£45,000 for a 25–40m² extension, depending on complexity, size, and location.

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3. Steelwork

Almost every kitchen extension requires at least one RSJ steel beam where you knock through the existing house wall. This is typically included in the builder's quote as a provisional sum, but the actual cost varies widely with complexity.

• Simple opening (single RSJ): £900–£1,600 supply and installation
• Complex steelwork (longer spans, corner posts, bifold openings): £3,000–£6,000+

My steelwork cost £7,750 across multiple invoices — an outlier caused by a cantilever design, a builder who made unauthorised changes to the structural engineer's spec, and two separate steel redesigns. A straightforward opening would have cost a fraction of that.

Typical steelwork: £3,000–£8,000. Always ask the structural engineer to specify the steelwork in their scope and ensure your builder prices it as a confirmed figure, not a provisional sum.

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4. Glazing (Windows, Bifolds, Roof Lights)

This is where cost ranges get enormous, driven almost entirely by what you choose.

Standard windows for a single-storey extension: £2,000–£5,000 supply and fit.

Aluminium bifold doors (3–5 panels, supply only): £3,150–£7,200. Add £600–£1,200 for installation labour.

Roof lights: £1,000–£3,000 each depending on size and specification.

My glazing was at the top end: HBD Systems roof lights (£11,748) plus Supreme Bifolds replacement doors after my original supplier went bust (£15,693). Total glazing: £27,441. For a standard single-storey with a French door and one roof light, you'd be looking at £4,000–£8,000.

Budget for glazing based on what you actually want. The gap between a basic door-and-window setup and a premium bifold-and-skylights configuration is £15,000+.

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5. Utility Meter Moves

If your gas or electricity meter is on the wall where the extension is being built, it must be moved before construction starts. This is done by your Distribution Network Operator (DNO) for electricity, and your gas network operator for gas.

• Gas meter relocation: £600–£1,200 (scheduled, without complications)
• Electricity meter relocation: £500–£1,200

I paid £808 for gas and £1,020 for electricity. Then on the day of the gas trench digging, the groundworker struck the gas pipe, triggering an emergency reroute. The emergency repair cost an additional £856, partially offset by a refund on the scheduled work.

Total utility costs (meter moves + trenching by a groundworker + emergency): £5,427.

If your meters don't need moving, this category is zero. If they do, budget £1,500–£3,000 for straightforward moves, more if you need trenching work.

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6. Electrics

A kitchen extension needs substantial electrical work: first fix cabling for sockets, lighting, underfloor heating controls, and cooker supply; second fix for installing fittings; and potentially a consumer unit upgrade.

• Extension electrics (both fixes): £1,500–£5,000 for a standard specification
• Additional fittings (chrome faceplates, dimmer switches, downlights): £200–£500 on top

My electrician quoted £3,290 for the core wiring (excluding fittings, which he bought separately). By the end, including consumer unit work, the move of the unit during construction, additional jobs, and materials, I had paid roughly £6,600 in total. Consumer unit upgrades and smart home additions (Ring doorbell, Hive thermostat, extra island sockets) drove that upward.

Typical extension electrics: £3,000–£6,000 for a well-specified kitchen.

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7. Plumbing

Plumbing scope varies the most of any trade. At minimum, you need hot and cold water to the sink and dishwasher; at maximum, you're rerouting a boiler, adding underfloor heating, installing a quooker tap, and running pipes for a fridge ice maker.

• Extension plumbing (full specification, excluding boiler): £5,000–£8,000
• Full scope including boiler work: £8,000–£18,000

My plumber's total (two invoices plus additional work) came to £10,394, including a Quooker boiling water tap and a water softener. The original quote was £10,400 — which turned out to be accurate, though spread across multiple invoices.

Plumbing is where costs can spiral. Every additional appliance — island tap, water softener, wine cooler — adds a pipe run and connection. Scope this carefully.

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8. Screed

If you're installing underfloor heating (which I'd recommend for a ground floor extension), the UFH pipes need to be embedded in screed. Liquid screed is the standard choice for UFH.

• Liquid screed (50m²): £2,000–£3,000
• Traditional sand-and-cement screed (50m²): £800–£1,500

My screed specialist cost £2,622 for liquid screed. The builder had quoted a provisional sum of £1,300 — roughly half the actual cost. Provisional sums for screed are almost always optimistic.

Budget for liquid screed at its actual rate: £18–£34 per m². Don't let a builder's provisional sum mislead you.

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9. Plastering

Screeding and plastering follow each other in sequence. Once the screed has dried (allow several weeks for liquid screed), the plasterer plasterboards the walls and ceiling and applies skim coats.

• Plastering a kitchen extension: £1,500–£3,500 depending on size and complexity

My plasterer's work across the extension was spread across multiple invoices and partly covered within the builder's labour. Standalone plaster costs for the extension area were approximately £2,000.

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10. Tiling and Flooring

Flooring and tiling is where taste-driven cost variance is highest.

• Porcelain floor tiles (supply and labour): £60–£120 per m²
• Wall tiles (supply and labour): £50–£100 per m²

I chose large-format 60x60 Bravestone Gray porcelain tiles. With 81m² of floor space and some wall tiling, the total came to £7,033: £3,933 for the tiles themselves (bought with a 20% trade discount) and £3,100 in labour.

For a 25m² extension with a reasonable tile choice:

• Floor tiling (25m²): £1,500–£3,000
• Kitchen wall splashback tiles: £500–£1,500

Total tiling and flooring: £2,000–£5,000 for a typical kitchen.

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11. Kitchen Fit-Out (Units, Worktops, and Fitting)

This category is entirely budget-dependent. The kitchen units themselves are a separate purchase — not included in any builder's quote — and the cost range is enormous.

• Kitchen fitter labour: £1,500–£3,500
• Kitchen units and appliances: £3,000 (flat-pack, self-sourced) to £50,000+ (fully bespoke)
• Stone worktop templating and fabrication: £1,500–£4,000 depending on material and length

The kitchen fit-out is the part of the project most directly under your control. Our kitchen — sourced through an independent kitchen designer — was in the mid-range. The fitter's labour was part of a wider arrangement.

For budgeting purposes, a mid-range kitchen for a 25–30m² extension runs £8,000–£20,000 including units, worktops, and fitting, but not appliances. Allow separately for appliances.

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12. Decoration

Once the plastering has dried and cured (at least 4 weeks, ideally longer), the decorator applies a mist coat and two finish coats.

• Decoration (painting) for a kitchen extension: £1,000–£2,500

My decoration came to approximately £1,188, spread across the kitchen, utility room, and some upstairs rooms affected by the build.

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13. Garden Reinstatement

Construction destroys the garden behind your house. Temporary fencing, concrete, mortar spills, and equipment storage leave the patio area in a state. Budget for making it good.

• Patio (supply and lay): £60–£120 per m² depending on material
• Garden clearance and reinstatement: £2,000–£8,000 depending on scope

My landscaping came to approximately £4,500 including patio laying, soak-away work, and a new front drive. The front drive was needed partly because the gas trench ran through it.

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14. Waste Disposal

During construction, you will fill multiple skips. The builder typically provides some skips within their quote, but extras are often charged separately.

• Builder's skip (6–8 yard): £200–£500 each
• Total waste budget for a full extension: £800–£1,500

My skip costs were spread across the build and garden work: at least three skips at around £240 each.

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What Drives Cost Up

In my experience, four factors blow extension budgets:

1. Steelwork complexity. A simple opening is cheap. Corner posts, cantilevers, and structural changes to upper floors are expensive. Worse, steelwork problems compound — once my builder made unauthorised changes to the spec, it cascaded into months of delays and additional fabrication costs.

2. Glazing choices. There is a £15,000+ gap between standard doors and a premium bifold setup. Decide early and budget accordingly.

3. Utility complications. If your meters need moving AND you discover utility pipes in the dig, costs escalate quickly. My gas pipe was struck twice during groundwork. This wasn't anyone's fault — the utility plans were inaccurate — but it cost several hundred pounds and days of delay.

4. Provisional sums. Builders use provisional sums for work they can't precisely price at quote stage: steelwork, screed, glazing, drainage. These sums are almost always optimistic. My screed provisional sum was £1,300; the actual cost was £2,622. Treat every provisional sum as a minimum, not a budget.

The 2026 Cost per Square Metre

Category	Typical Range (2026)
Builder's structure only	£1,100–£1,500/m²
All-in (excluding kitchen units and appliances)	£1,800–£2,800/m²
All-in (including mid-range kitchen)	£2,000–£3,500/m²

These figures are based on UK national averages. London adds 20–30% to most trade costs.

How Much Contingency Do You Really Need?

Every guide says budget 10–15% contingency. My experience says this is not enough.

My build overran by £75,000 against the builder's original quote — though it's fairer to say the original quote never covered the full scope. When I look at unexpected costs only (the ones nobody saw coming), the overruns included:

• Steelwork redesigns: £3,500
• Insulation upgrade required by BCO: £773
• Bifold supplier insolvency, replacement premium: ~£3,000 extra
• Emergency gas pipe fix: ~£800
• Screed provisional sum shortfall: £1,300

That's about £9,000 in genuinely unforeseeable overruns — roughly 20% of the builder's quote.

Budget 20% contingency on the total all-in figure, not just the builder's quote. On a £80,000 project, that means keeping £16,000 in reserve. It feels like a lot. By the end, you will wish you had it.

The Complete Budget Summary

Category	Typical (25m²)	My Build (55m²)
Professional fees (architect, fees)	£3,000–£5,000	£3,560
Builder's structure	£28,000–£40,000	~£45,000
Steelwork	£3,000–£6,000	£7,750
Glazing (bifolds, windows, rooflights)	£4,000–£12,000	£27,441
Utility meter moves	£0–£6,000	£5,427
Electrics	£3,000–£6,000	£6,600
Plumbing	£5,000–£12,000	£10,394
Screed	£1,500–£3,000	£2,622
Plastering	£1,500–£3,500	~£2,000
Tiling and flooring	£2,000–£5,000	£7,033
Kitchen units (mid-range)	£8,000–£20,000	not shown
Decoration	£1,000–£2,500	£1,188
Garden reinstatement	£2,000–£8,000	£4,500
Waste disposal	£800–£1,500	~£800
Total (before kitchen units)	£63,000–£110,000	~£120,480

My build figures include costs at 2021–2024 prices. Adjust upward by approximately 10–15% for 2026 material and labour inflation.

What I Would Do Differently

Get a full scope breakdown before signing anything. My builder's quote covered the structural work. Everything else — electrics, plumbing, glazing, screed, kitchen fitting — was either in provisional sums or simply not on the quote. I didn't realise the true scale of what was missing until the invoices started arriving.

Always ask your builder for a line-by-line breakdown, then check each line against the categories above. If anything is missing, ask where it sits in the budget.

Budget based on what you actually want, not what's vaguely implied by a headline figure. The bifold doors that turn a kitchen extension into something special cost £10,000–£25,000 more than a standard French door setup. If you want them, budget for them explicitly — don't hope the builder's provisional sum will cover it.

Keep 20% contingency, not 10%. Construction throws surprises. Ground conditions, structural discoveries, BCO requirements, supplier failures — any of these can add thousands. A 20% contingency on the all-in figure gives you room to absorb them without crisis.

For a full walkthrough of the sequence, what happens at each stage, and what building control inspects, see our guide on the complete timeline for project managing a kitchen extension.