Kitchen Extension Cost UK 2026: Full Price Guide for Single-Storey Additions

Quick Answer

A single-storey kitchen extension in the UK costs £1,500–£2,500 per square metre for the structure. A common 3×4m (12m²) kitchen extension typically costs £25,000–£45,000 for the build, plus £8,000–£25,000 for kitchen units and appliances. Total project costs including kitchen fit-out: £35,000–£70,000. London and the South East add 20–30%. The work takes 8–16 weeks. Planning permission is often not required under permitted development, though this depends on the size and location.

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Why Kitchen Extension Costs Vary So Much

Two identically sized kitchen extensions in the same street can cost £20,000 or £50,000. The variables that drive price:

Structural complexity: A simple flat-roof extension with two new external walls is cheaper than a pitched-roof extension with multiple corners, rooflights, and bi-fold doors. Structural steel requirements vary by span.

Specification: A basic extension with standard double-glazed French doors, a flat roof, and standard brickwork is at the bottom of the price range. An extension with large aluminium bi-fold doors, a lantern roof, polished concrete floor, underfloor heating, and roof-integrated skylights sits at the top.

Foundation type: Clay soils may require deeper, more expensive foundations. Strip foundations are cheapest; reinforced raft or pile foundations significantly more expensive.

Existing rear access: If the builder has no vehicle access to the rear, materials need to be carried through the house — adding time and cost to every delivery.

Kitchen fit-out: The structure and the kitchen are separate costs. A flat-pack kitchen fitted by your builder adds £3,000–£8,000. A bespoke kitchen adds £15,000–£40,000+.

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Cost Per Square Metre: What to Expect

These are London-adjusted downwards — outside London, reduce by 20%.

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Typical Kitchen Extension Sizes and Costs

Note: extending beyond 3–4m depth (for mid-terraced houses) typically requires planning permission. Detached houses have more permitted development flexibility.

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What's Included in a Kitchen Extension Build Cost

A complete build quote should cover:

Groundworks and foundations: excavation, concrete strip or raft foundations, damp-proof membrane

Structure: external walls (brick/block or timber frame), internal wall removal and steel beam installation if required, roof structure

Roofing: flat roof (with GRP or EPDM waterproofing) or pitched roof (tiles to match existing), rooflights if specified

External finish: brickwork to match or contrast existing, render, or cladding

Windows and doors: supply and installation of bi-fold, French, or sliding doors; rear window if required; any rooflights

Insulation: floor, wall, and roof insulation to current Part L Building Regulations

First fix and second fix: electrics, plumbing rough-in, plastering, skirting, and architrave

Floor screed: ready for floor covering (not including the covering itself)

Building regulations: application, inspections throughout, and completion certificate

What's typically excluded: kitchen units and appliances, floor covering, decoration, landscaping, structural engineer's fees (usually separate £300–£800)

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Labour Rates: What Builders Charge for Extensions

Extension work involves multiple trades typically managed by a main contractor:

Labour typically represents 40–50% of total extension cost. For a £35,000 extension, expect £14,000–£18,000 in labour.

Most builders quote extensions as fixed-price contracts. This protects you from overruns and is the industry standard for this type of work. Insist on a fixed-price contract with a detailed specification — never proceed on a time-and-materials basis for an extension.

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Planning Permission: Do You Need It?

Permitted development (no planning required) for single-storey rear extensions:

• Up to 4m depth on a detached house
• Up to 3m depth on semi-detached or terraced houses
• Maximum height 4m (and no higher than the existing eaves)
• No side extensions on designated land or properties subject to Article 4 directions

Prior approval (simplified application): Extensions of 3–8m (detached) or 3–6m (other) require a prior approval application — neighbours are consulted but approval is usually straightforward.

Full planning permission required: Extensions exceeding the above dimensions, side extensions on most properties, properties in conservation areas, listed buildings, or where Article 4 removes permitted development rights.

Always check with your local planning authority or a planning consultant before assuming permitted development applies.

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Structural Engineer and Architect Fees

For a standard single-storey extension, fees:

• Structural engineer: £300–£800 (required for all extensions with load-bearing wall removal or steel beams)
• Architect/designer: £1,500–£5,000 for drawings and planning application (often not required for permitted development; useful for complex designs)
• Planning application fee (England): £258 for most householder applications

These are in addition to the build cost and are typically paid directly to the professionals rather than through the builder.

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How Long Does a Kitchen Extension Take?

The kitchen design and planning phase (choosing units, appliances, worktop) should happen in parallel with the build phase, not after. Lead times for bespoke kitchens run 8–14 weeks — order immediately after foundations are in to avoid your build finishing before the kitchen arrives.

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Frequently Asked Questions

How much does it cost to knock through from the existing kitchen into the extension? Removing a load-bearing rear wall requires a structural steel beam. Depending on span, the steel supply and installation adds £2,000–£5,000 to project cost. A structural engineer's calculations are required.

Is it cheaper to build up (add a storey) or out (single-storey extension)? For kitchen space specifically, single-storey outward extension is almost always cheaper. Adding a storey involves significantly more structural work and usually requires planning permission. Two-storey extensions (e.g., adding kitchen below and bedroom above) are more complex but better value per square metre than two separate projects.

What return will I get on a kitchen extension? A well-specified kitchen extension typically adds more value than it costs in areas with strong property markets. A £40,000 extension that converts a small galley kitchen into an open-plan kitchen/dining room can add £50,000–£80,000 of value in the right location. In lower-value property markets, the return may not recover the full cost.

Can I live in the house during a kitchen extension? Usually yes, though you'll be without a usable kitchen during construction. Plan for a temporary kitchen (microwave, kettle, camping stove in another room) for 8–12 weeks. The knock-through from existing to new space happens at the end of the build, minimising disruption.

What is the best foundation type for a kitchen extension? Strip foundations are standard for most extensions on stable ground. On clay soils or where there are tree roots nearby, deeper or reinforced foundations may be required. Your structural engineer will advise after a site investigation.