Kitchen Extension Cost UK 2026: Full Price Guide for Single-Storey Additions
Written by Tom Ellis · Senior Trades Editor
Last updated: August 2026
Last updated: August 2026 · United Kingdom
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.
Cost Per Square Metre — UK 2026
| Specification | Cost per m² (build only, excl. kitchen) |
|---|---|
| Basic (flat roof, standard spec) | £1,500–£1,800/m² |
| Mid-range (pitched roof, bi-folds) | £1,800–£2,200/m² |
| High specification (lantern roof, UFH, premium glazing) | £2,200–£2,800/m² |
| Premium (bespoke glazing, structural steel frame) | £2,800–£4,000/m² |
Outside London — reduce by 20% for regions beyond the South East.
Typical Extension Sizes and Build Costs
| Extension size | Floor area | Mid-range build cost |
|---|---|---|
| 3m × 3m | 9m² | £18,000–£27,000 |
| 3m × 4m | 12m² | £25,000–£36,000 |
| 4m × 4m | 16m² | £32,000–£48,000 |
| 4m × 6m | 24m² | £48,000–£70,000 |
| 5m × 7m | 35m² | £65,000–£100,000 |
What's Included in a Kitchen Extension Build Cost
- Groundworks and foundations: Excavation, concrete strip or raft foundations, damp-proof membrane
- Structure: External walls, internal wall removal and steel beam installation if required, roof structure
- Roofing: Flat roof (GRP or EPDM waterproofing) or pitched roof with tiles to match existing; rooflights if specified
- External finish: Brickwork to match existing, render, or cladding
- Windows and doors: Supply and installation of bi-fold, French, or sliding doors; rooflights
- Insulation: Floor, wall, and roof insulation to 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, and completion certificate
Typically excluded:Kitchen units and appliances, floor covering, decoration, landscaping, structural engineer's fees (usually separate £300–£800).
Labour Rates: What Builders Charge for Extensions
| Trade | Day rate (outside London) |
|---|---|
| Bricklayer | £180–£350/day |
| Carpenter | £200–£350/day |
| Roofer | £200–£320/day |
| Plasterer | £180–£300/day |
| Electrician | £250–£400/day |
| Plumber (heating and underfloor) | £250–£400/day |
Labour typically represents 40–50% of total extension cost. Most builders quote extensions as fixed-price contracts — insist on this rather than time-and-materials.
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)
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, properties in conservation areas, listed buildings, or where Article 4 removes permitted development rights. Always check with your local planning authority before assuming permitted development applies.
How Long Does a Kitchen Extension Take?
| Stage | Duration |
|---|---|
| Design and planning (if required) | 8–16 weeks |
| Groundworks and foundations | 1–2 weeks |
| Structure (walls and roof) | 3–5 weeks |
| First fix, plastering, second fix | 3–5 weeks |
| Kitchen fit | 1–2 weeks |
| Total (build phase) | 8–16 weeks |
Order the kitchen while foundations are going in — bespoke kitchens have 8–14 week lead times. Don't wait until the build is finished.
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 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.
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) for 8–12 weeks. The knock-through from existing to new space happens at the end of the build.
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.
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