Kitchen Extension Costs UK — Single Storey, Rear and Side Return Extension Pricing Guide (2026)
A kitchen extension is the most popular domestic building project in the UK — and consistently the one that delivers the highest return on investment for homeowners. Knocking through the back and extending creates the open-plan kitchen-diner that buyers pay a premium for, without the cost and upheaval of moving. But prices have climbed hard since 2021: materials inflation, wage increases, and the surge in demand for skilled trades means that what cost £35,000 four years ago often costs £50,000 or more today. This guide gives builders and homeowners accurate 2026 UK figures for every type of kitchen extension, a full cost breakdown by trade, and a clear picture of planning, party wall, and structural requirements.
Kitchen extension costs at a glance (2026)
All figures below are complete project costs including all trades, materials, architect or designer fees, structural engineer, building regulations, and scaffolding. They represent what the end client pays for a fully finished, signed-off project.
| Extension type | Cost per m² | Typical project cost |
|---|---|---|
| Single storey rear (mid-range) | £1,500 – £2,500 | £30,000 – £50,000 (20m²) |
| Single storey rear (premium spec) | £2,500 – £3,500 | £50,000 – £80,000 (20m²) |
| Side return (London terrace) | £1,800 – £3,200 | £30,000 – £60,000 |
| Wrap-around (rear + side) | £2,000 – £3,500 | £50,000 – £120,000+ |
UK averages 2026. London and South East: add 20–30% to figures above. Costs exclude VAT where applicable.
Extension types in detail
Single storey rear extension
The most common kitchen extension type in the UK. A 20m² footprint is the standard benchmark — deep enough to create a meaningful open-plan kitchen and dining area without eating the entire garden. At mid-range specification (blockwork cavity walls, flat or monopitch roof, aluminium bi-fold or French doors, mid-range kitchen), expect £1,500–£2,500/m², putting a typical 20m² project at £30,000–£50,000 fully finished. Premium specification — roof lantern, structural glazing, underfloor heating, high-end kitchen fit-out — pushes cost per m² to £2,500–£3,500 and the total project to £50,000–£80,000+. The single biggest variables are the kitchen fit-out budget and the glazing package.
Side return extension
Fills in the narrow passageway that runs down the side of Victorian and Edwardian terraced and semi-detached houses. Typically 2–3m wide and 6–9m long, a pure side return does not deliver dramatic floor area gains — but when combined with opening up the existing kitchen footprint, it transforms a cramped galley into a proper kitchen-diner. The structural complexity is higher than a straightforward rear extension: the existing side wall is usually load-bearing, the roof junction is complex, and working in a narrow space with plant and materials is slower. For a typical London terrace, budget £30,000–£60,000 for a side return extension. At the upper end of that range you are getting a glazed roof over the full length of the return, quality aluminium joinery, and a mid-to-premium kitchen.
Wrap-around extension (rear + side combined)
Combines a rear extension with a side return to create a large L-shaped ground floor extension. The most dramatic transformation possible on a terraced or semi-detached house — and the most structurally complex. The junction between the rear and side sections requires careful engineering; the existing corner of the house typically needs a steel frame to maintain structural integrity. Cost: £50,000–£120,000+ depending on the footprint and specification. Planning permission is almost always required. Clients who commission wrap-around extensions typically have larger budgets and longer wish lists — get written specification sign-off on every element before pricing.
Full cost breakdown by trade
The figures below are what you should expect to pay subcontractors and suppliers for a typical 20m² single storey rear kitchen extension in 2026. These are subcontract and materials costs — add your project management margin (15–25%) on top.
Bi-fold doors and roof lanterns
Glazing is the single most variable cost on a kitchen extension and the item clients most often upgrade after the quote is agreed. Get written specification sign-off before ordering anything.
Bi-fold and sliding doors
A 3m bi-fold door set in aluminium costs £2,500–£5,000 supply and fit at mid-range (good quality uPVC or standard aluminium). Premium powder-coated aluminium systems from Schuco, Origin, or similar brands run £4,000–£8,000 for the same opening. Sliding door systems (which many architects now specify in preference to bi-folds) sit at a similar price point. French doors for the same opening are £1,500–£3,000 — significantly cheaper and often more practical where the garden is small. Where the client wants a full-width glazed rear wall, budget £5,000–£12,000+ for the complete glazing package.
Roof lanterns
A roof lantern over a flat or low-pitch extension roof is the detail clients see on Instagram and want most. A standard aluminium roof lantern in the 1.5m × 1m range costs £1,500–£2,500 supply and fit. A 2m × 3m lantern — the size that makes a real impact — runs to £3,500–£7,000. Structural glazing systems and bespoke lanterns can reach £10,000+. The structural beam that spans the opening for a large lantern adds another £500–£1,500 depending on the span. Always include the structural engineer's cost for lantern beam design if the opening is more than 2m in any direction.
Permitted development vs planning permission
Whether a kitchen extension needs a planning application depends on the extension type, size, and the property's location. Getting this wrong can mean enforcement action and demolition costs — not a risk worth taking.
Single storey rear — permitted development rules
Single storey rear extensions fall within permitted development (PD) up to 3m depth on an attached (terraced or semi-detached) house and 4m depth on a detached house, provided the extension does not exceed 4m in height. Larger extensions — up to 6m on attached and 8m on detached properties — may be possible under the Neighbour Consultation Scheme (notifiable PD). Under this route the local planning authority notifies adjoining owners and has 42 days to consider objections before confirming PD rights. Always advise clients to obtain a Lawful Development Certificate even for clear-cut PD cases — it protects them on sale. LDC application fee in England (2026): £258.
Side return and wrap-around extensions
Side extensions are generally not permitted development if the flank elevation faces a highway. In all other cases a single storey side extension may technically fall within PD if it does not exceed half the width of the original house — but in practice most side return and wrap-around projects require a full planning application. Planning application fee in England (2026): £258 for a householder application. Programme: allow 8–13 weeks for the application and decision, plus the pre-application engagement period if used.
Neighbour impact and light
Planning officers weigh the impact on neighbouring amenity heavily, particularly loss of light and overlooking. A rear extension that shadows a neighbour's kitchen or garden is likely to generate objections. The 45-degree rule — where the extension must not cross a 45-degree line drawn from the centre of the neighbour's nearest window — is commonly applied. Even where an extension is permitted development, a neighbour can still raise objections through the Neighbour Consultation Scheme. Advise clients to speak to their neighbours before serving formal notices wherever possible.
Conservation areas and listed buildings
Permitted development rights are withdrawn or significantly restricted in conservation areas, National Landscapes (previously Areas of Outstanding Natural Beauty), and for listed buildings. Any extension to a listed building requires listed building consent as well as any required planning permission. Do not assume PD applies without checking the planning constraints register for the specific property.
Party wall agreement: when you need one and what it costs
The Party Wall etc. Act 1996 applies whenever work is carried out on or close to a shared wall or boundary. Kitchen extensions on terraced and semi-detached houses almost always trigger the Act.
- →Work on a shared (party) wall. Side return extensions almost always involve the shared flank wall of a terraced or semi-detached property. Any work to this wall — cutting in beams, raising the height, or removing sections — triggers the Act and requires a Party Wall Notice to be served on the affected neighbour.
- →Excavation near neighbouring foundations. New foundations within 3m of the neighbour's existing foundations (or within 6m if the new foundations go deeper than a 45-degree line drawn from the neighbouring foundation) also trigger the Act — covering most extension footprints on a typical terraced street.
- →Timescales. Party Wall Notices must be served at least one to two months before work begins. If the neighbour consents, you can proceed. If they dissent or do not respond within 14 days, a surveyor must be appointed to draw up a Party Wall Award. The building owner pays the costs in most cases.
- →Surveyor costs. Party Wall surveyor fees run to £700–£1,500 per affected neighbour for a straightforward Award. On a mid-terrace with two affected neighbours, budget £1,400–£3,000. Complex disputes or contentious projects cost more. Always flag this to the client in writing before work starts — it is a surprise cost that regularly causes friction if not discussed upfront.
Structural engineer and architect: when you need them
Structural engineer
A structural engineer is required for any kitchen extension that involves an opening in an existing structural wall, a roof lantern wider than 2m, or a long-span steel beam. On a typical rear extension knocking through from the existing kitchen into the new space, you need beam calculations and drawings to satisfy building control. Structural engineer fees: £500–£1,500 for a domestic extension. Some builders charge this back to the client as a pre-contract cost; others absorb it as a cost of winning the work. Either is acceptable — what is not acceptable is quoting foundation and beam sizes without engineering input and hoping the numbers are right.
Architect: when you need one and when you don't
For a straightforward single storey rear extension under permitted development, an architect is not legally required. Many builders manage the planning drawings and building regulations package themselves or use a local architectural technician (typically £800–£2,500 for drawings only). Where an architect adds genuine value: complex planning applications in sensitive areas, listed buildings, wrap-around extensions requiring detailed structural design coordination, and premium projects where the client expects interior design input alongside the build. Architect fees for a full service on a domestic extension run to 10–15% of build cost. On a £60,000 extension, that is £6,000–£9,000 — money well spent on a complex project, harder to justify on a straightforward PD rear extension.
Project management: main contractor vs managing trades yourself
Kitchen extensions involve multiple trades working in sequence — groundworker, bricklayer, roofer, electrician, plumber, plasterer, kitchen installer, flooring fitter, decorator — and the programme only works if each trade finishes on time and the next arrives promptly. Homeowners who try to manage this themselves on a fixed budget consistently underestimate the coordination overhead and the cost of delays when a trade overruns.
A main contractor who manages the full programme charges a margin (typically 15–25% on subcontract costs) for doing so. On a £40,000 project the contractor's management margin is £6,000–£10,000. That is real money — but so is the cost of a two-week delay caused by a missed handover, a plasterer who turns up before the first fix is done, or a kitchen delivery that arrives before the screed has cured. For most clients on projects over £30,000, a main contractor is better value than self-management even when the margin is visible on the quote.
Groundwork surprises: what to watch for
- →Soil conditions. Clay soils prone to shrinkage and swelling (common across London, the Midlands, and parts of the South East) require deeper strip foundations or engineered solutions. Made ground — garden areas that have been built up over decades with demolition rubble, ash, or general fill — cannot support standard strip foundations without excavating to undisturbed ground. High water table on riverside or low-lying sites triggers tanking or drainage requirements. A soil investigation (desk study or trial pit) costs £500–£1,500 and is cheap relative to the cost of underquoting foundations on a difficult site.
- →Existing drainage. Back gardens on Victorian terraces frequently contain original Victorian clay drainage runs that are not on any plans. Striking a drain during groundworks means a drainage survey, potential diversion, and building control notification. Budget a drainage contingency of £1,000–£3,000 on any project where the existing drainage layout is uncertain.
- →Existing foundations. Where the extension footprint is adjacent to the existing house foundations, the depth and condition of those foundations determines whether underpinning is required. On Victorian and Edwardian properties, existing foundations are typically shallow (600–900mm) — sufficient for the original structure but potentially insufficient once the load distribution changes with an extension. Always flag this as a risk item in the quote with a provisional sum.
- →Tree proximity. A mature tree within 5–10m of the extension footprint can require root barrier installation, deeper foundations, and a Tree Protection Plan agreed with the council. The structural engineer and arboriculturalist need to be involved before groundworks start. The cost of getting this wrong is subsidence — an insurance claim, not a builder's problem on paper, but catastrophic for a client relationship and your reputation.
Regional variation: London premium and national averages
London and the South East consistently sit 20–30% above the national average for extension costs. The drivers are higher labour rates across all trades, higher material delivery costs, more difficult access in dense urban areas, and a planning environment that frequently requires more detailed applications and more specialist input. The figures below compare a typical 20m² rear kitchen extension across regions:
| Region | Typical 20m² rear extension |
|---|---|
| London and South East | £45,000 – £80,000 |
| East of England | £38,000 – £65,000 |
| South West | £35,000 – £60,000 |
| East Midlands / West Midlands | £32,000 – £55,000 |
| North West / Yorkshire | £30,000 – £52,000 |
| Scotland / Wales / North East | £28,000 – £48,000 |
Mid-range specification. Premium spec adds 30–50% across all regions.
Build timeline: what to expect
A typical 20m² rear kitchen extension runs 12–20 weeks from contract signature to practical completion. The programme below assumes planning is already in place or permitted development confirmed.
Total on-site programme: 12–18 weeks for a 20m² rear extension. A side return or wrap-around extension with higher structural complexity runs 16–22 weeks. Plaster and screed drying time cannot be rushed — a screed laid in week eight needs at least three to four weeks before floor finishes go down. Include these waiting periods explicitly in your programme so clients understand why trades are not on site every day.
Quoting guide for builders doing kitchen extensions
Kitchen extensions are high-value, long-programme jobs. Underquoting is the single biggest financial risk on this type of work. Here is how to structure the quoting process to win work at the right price.
Site visit is mandatory
Never price a kitchen extension from drawings alone. Walk the full footprint: check access for machinery and materials, look for signs of tree root activity, locate existing drainage runs, check the condition of the existing rear wall and roof junction. Any of these can materially affect your price. A 30-minute site visit that surfaces a drainage diversion requirement saves a £2,000–£5,000 omission from the quote.
Use provisional sums for high-variability items
Include provisional sums for: foundations (pending soil investigation), glazing (pending client specification sign-off), kitchen fit-out (pending kitchen selection), and any drainage works. Present these clearly in the quote with written explanations of what will cause the provisional sum to move up or down. This is not a way to avoid commitment — it is a way to be transparent about where the real cost risk sits and to protect yourself when clients change their minds.
Break out prelims as a separate line item
Preliminaries on a 14–18 week kitchen extension project are significant: scaffolding hire (£1,500–£3,000), skip hire across the programme, plant hire, welfare facilities, and general labourer time. Present these as a distinct section of the quote rather than spreading them invisibly across trade costs. This protects your margin and prevents clients from comparing your trade costs line-by-line with cheaper quotes that have buried their prelims in the unit rates.
Stage payment schedule
A kitchen extension requires a milestone payment schedule. Five stages is standard: contract signing (10%), foundations complete (20%), watertight structure (25%), first fix complete (25%), practical completion and BC sign-off (20%). Include the payment schedule in the quote, not as a separate document issued after acceptance. Clients who see a clear payment programme before signing have fewer disputes about when payments fall due.
How Trade2Base helps builders win and track extension work
Kitchen extension enquiries are the highest-value leads a domestic builder receives. They come from multiple channels — Google Search, Checkatrade, Houzz, word of mouth, local Facebook groups, previous client referrals — and the conversion rates, average job values, and cost per lead vary significantly across those channels. Most builders have no visibility of which channel is actually delivering the work that converts and makes money.
Trade2Base tracks every enquiry from first contact through to signed contract and completed job. When a kitchen extension enquiry comes in, Trade2Base records where it came from, whether it converted to a quote, whether the quote was won, and the final job value. Over time, this gives you the data to answer the questions that actually determine whether your marketing budget is working: Is your Google Ads spend producing extension enquiries at a cost per lead that makes sense given your conversion rate and average job value? Are referral clients more likely to accept your quote than Checkatrade clients? Which channel produces the clients who pay on time and do not generate variations?
For builders running extension projects worth £30,000–£120,000+, understanding marketing attribution is not a nice-to-have — it is the difference between a marketing budget that grows the business and one that wastes money on channels that produce tyre-kickers.
Win more extension projects
Trade2Base shows builders which marketing channel brings in extension enquiries that convert — so you quote the right jobs and win the right work.
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