Kitchen Extension Costs in London: What to Budget in 2025

Kitchen extension costs are driven by four main variables:

**1. Size of the extension**: The single biggest cost driver. A 12m2 extension at the back of a house costs significantly less than a 35m2 wrap-around. Material quantities, foundation lengths, roof area, and trade time all scale with floor area.

**2. Specification level**: A standard-finish kitchen extension with a mid-range kitchen, tiles, and painted walls is very different in cost from a high-specification project with structural glazing, bespoke joinery, stone worktops, and underfloor heating. The difference between a basic and a high-spec finish on the same extension can be £20,000–£50,000+.

**3. Structural complexity**: A straightforward rear extension with a simple flat roof and no structural opening into the existing house is the cheapest structural scenario. Add a large structural opening (requiring a steel RSJ), a rear wall knocked through, or drainage diversion, and structural costs increase significantly.

**4. Location within London**: Labour and material costs vary across Greater London. Central and south-west London typically commands higher contractor rates than outer boroughs. Allow 10–20% premium for central and premium south-west London postcodes.

Based on London market conditions in 2025:

**Small rear kitchen extension (12–18m2 floor area)** Suitable for a modest improvement to an existing kitchen, adding a dining area. Flat roof with one rooflight, single structural opening. - Basic finish: £35,000–£55,000 - Mid-range finish: £55,000–£75,000 - High specification: £75,000–£100,000

**Medium rear kitchen extension (20–30m2 floor area)** The most common project: an open-plan kitchen-diner, typically 3–4m deep extension across the full width of the rear elevation. Flat roof with lantern or two rooflights. - Basic finish: £55,000–£80,000 - Mid-range finish: £80,000–£120,000 - High specification: £120,000–£175,000

**Large extension or wrap-around (30–45m2 floor area)** Full-width open-plan across rear and side return, or deeper extension creating a full family room addition. - Basic finish: £85,000–£130,000 - Mid-range finish: £130,000–£185,000 - High specification: £185,000–£280,000+

These figures include the building works and kitchen supply and installation. They do not include professional fees (architect, structural engineer, planning) or landscaping.

A complete kitchen extension cost can be broken down into the following elements:

**Structure (40–50% of total cost)** - Demolition and enable works - Foundations and substructure - Walls and external envelope - Roof structure and weatherproofing - Structural opening(s) into existing house - Drainage alterations where required

**First-fix services (12–18%)** - Electrical first fix (rewiring, new circuits, consumer unit upgrades) - Plumbing first fix (underfloor heating pipework, boiler extensions, radiators) - Heating system works

**Insulation and plastering (8–12%)** - Wall and floor insulation to Part L compliance - Screeding or timber floor deck - Plastering and skim coat

**Kitchen supply and installation (15–30% — the widest variable)** - Kitchen units: IKEA/Wickes level at £3,000–£8,000; mid-range (Howdens, Wren, Magnet) at £8,000–£20,000; bespoke joinery at £25,000–£80,000+ - Worktops: laminate (£500–£1,500), quartz/granite (£2,000–£6,000), stone (£4,000–£15,000+) - Appliances: £2,000–£15,000 depending on brand and specification

**Second-fix and finishing (10–15%)** - Tiling, flooring, decoration - Doors, skirting, architrave - Electrical second fix (sockets, switches, lights) - Plumbing second fix (sinks, taps)

**Glazing (variable — can be 5–20% of total)** - Standard rear doors: £1,500–£4,000 per set - Bi-fold doors: £4,000–£12,000 for 3–4 panels - Roof lantern: £4,000–£9,000 - Structural glazed roof: £600–£1,200/m2

Professional fees are often excluded from contractor quotes and ballpark estimates. Budget separately for:

- **Architect / architectural designer**: 8–12% of construction cost for full design service; fixed-fee alternatives from £4,000 for drawings only - **Structural engineer**: £600–£2,500 for calculations and specification - **Planning application fee**: £258 (if required) - **Building Regulations / Building Control**: £800–£2,000 (full plans route) - **Party wall surveyor**: £800–£2,000 per side (if applicable) - **Quantity surveyor / cost consultant** (optional): £800–£2,500

Allow 12–15% of construction cost for professional fees on a typical kitchen extension project.

**Costs more than average**: - Conservation area (matching bricks, pitched roof requirement, heritage windows) - Drainage diversion of soil stack or shared drain - Party wall complexity (multiple neighbours, structural issues) - High-water-table or poor ground conditions requiring deeper foundations - High specification kitchen, stone surfaces, bespoke joinery - Structural glazing or full-width roof glazing - Underfloor heating throughout - High-end appliances

**Costs less than average**: - Simple single-storey rear extension in a straightforward semi-detached house - No drainage complications - No structural openings or minimal opening - Mid-range kitchen from a modular supplier - Standard bifolds and rooflight rather than structural glazing - Outer London location with lower contractor rates

**Common budget mistakes**: - Underestimating the kitchen itself — many clients budget heavily for the structure but then find the kitchen and glazing cost as much as expected for the whole project - Forgetting professional fees - Not allowing for contingency (recommend 10–15% of construction cost) - Treating the ballpark as the final price before scope and specification are fixed