Kitchen Extension Costs in London 2025: From £50K to £150K+ Explained

The most common kitchen extension types in London and their planning status: Single-storey rear extension: extends the kitchen at the rear of the property. Typically 3-6m deep and the full or partial width of the house rear. Planning status: permitted development (PD) for a depth of up to 6m from the original rear wall on a terraced or semi-detached house (8m for detached) under the Prior Approval / Householder Permitted Development rights (GPDO Part 1 Class A). In a conservation area: rear extensions are generally PD up to the full extent of Class A limits, but materials must match the existing house. London boroughs: some London boroughs have removed Class A PD rights through Article 4 Directions — check before assuming PD. Wrap-around extension: combines a rear single-storey extension with a side infill or side return extension, creating an L-shaped ground floor extension. Very popular in inner London where the narrow alley or side return between the terrace and the boundary wall can be filled. Planning status: the side return element (where the side elevation faces a highway) will typically require full planning permission even where the rear element is PD. Many London boroughs have restrictions on side return extensions in conservation areas. The total extension creates a larger footprint, with a distinctive wide-spanning open-plan space at the rear. Double-storey rear extension: extends both the ground floor (kitchen extension) and the first floor (typically an additional bedroom or bathroom). Planning status: requires full planning permission in most London locations (double-storey rear extensions are not PD). Basement extension with rear: combines an excavated basement with a rear extension, creating two additional levels of living space. Requires planning permission. Always requires structural engineer input.

A typical single-storey rear extension for an open-plan kitchen, dining, and family room in inner London (2025 cost data): Extension shell (structure, roof, external doors, and windows): For a 4m x 5m (20 sq m) single-storey rear extension: Groundworks (excavation, strip foundations in London clay 1.0-1.5m deep, drainage connection): £8,000-£15,000. Structural walling (blockwork cavity walls, insulation, brick facing outer leaf to match existing): £6,000-£12,000. Roof structure (flat roof with warm deck build-up: vapour barrier, PIR insulation, OSB deck, single-ply membrane; or pitched roof tiled to match): £6,000-£15,000 for a flat roof; £10,000-£22,000 for a pitched roof. External doors and glazing: bi-fold door or sliding door across the full rear of the extension (3m-5m wide): £4,000-£14,000 for PVCu/aluminium bi-fold; £6,000-£18,000 for thermally broken slim-frame aluminium (premium); roof lights (2 x Velux-type or flat roof light over the extension): £1,500-£5,000. Structural opening in the rear wall of the existing house (to connect extension to existing kitchen and create open-plan space): steel beam, padstones, propping, and making good: £3,000-£8,000 (depending on span, floor above, and structural configuration). Total extension shell: £28,000-£67,000 for a 20 sq m single-storey rear extension in London. For a wrap-around extension (including side return fill, typically adding 8-15 sq m to the rear extension): add £15,000-£35,000 to the shell cost above. Internal fit-out (kitchen, finishes, M&E): Kitchen supply (mid-specification from a trade supplier such as Howdens, Benchmarx, or Magnet, with a standard quartz or laminate worktop): £8,000-£18,000. Kitchen supply (bespoke or higher specification — Wren, John Lewis Kitchens, Smallbone, Tom Howley): £20,000-£60,000+. Kitchen installation (carcass fitting, worktop cutting, plumbing connections): typically included in the kitchen company's installation package or quoted separately by the main contractor as part of the second fix package. Plastering and internal finishes (walls and ceiling in extension, making good to existing house where structural opening was formed): £3,000-£8,000. Flooring (porcelain tile or engineered oak throughout extension and into existing kitchen — 35-50 sq m supply and install): £4,000-£12,000. M&E (electrical, plumbing, underfloor heating): electrical first fix and second fix for extension (sockets, switches, downlights, extractor fan): £2,500-£6,000. Gas or electric underfloor heating (wet UFH connected to existing boiler, or electric mat system): wet UFH supply and installation for 20 sq m: £2,500-£6,000. Plumbing modifications (moving kitchen sink, adding dishwasher connection, connecting extension drainage): £1,500-£4,000. Decoration (painting, skirting boards, architraves): £2,000-£5,000. Total internal fit-out (mid-specification): £25,000-£55,000 (excluding premium kitchen).

Compact single-storey rear extension (20 sq m, mid-specification kitchen, standard bi-fold, flat roof): total project cost: £55,000-£90,000. Medium single-storey rear extension (25-35 sq m, mid-upper kitchen specification, slim-frame aluminium doors, structural rooflights, wet UFH, porcelain tile floor): total project cost: £75,000-£120,000. Wrap-around extension (rear 20 sq m + side return 10-15 sq m = 30-35 sq m total, mid-upper specification): total project cost: £90,000-£145,000. Kitchen extension with basement and rear (rear 20 sq m + excavated 30 sq m basement): total project cost: £200,000-£350,000+ depending on complexity. What drives the variance in kitchen extension costs in London: Roof specification: flat roof (warm deck with single-ply membrane) is the most common choice for rear extensions and is generally the most cost-effective. A pitched tiled roof to match the existing house is more expensive (more complex roof structure) but may be preferred in conservation areas or where planning requires matching materials. A lantern roof or large structural roof light above the dining area significantly increases cost. Glazed door specification: PVCu bi-fold is the entry-level option. Aluminium bi-fold is the standard mid-market choice. Slim-frame aluminium (Schuco, Smart Visofold, Origin) is the premium option. Slide-and-stack or pocket door (fully receding into the wall) is the top-spec option. Premium glazed door systems add £5,000-£15,000 to the standard bi-fold cost. Kitchen specification: the single biggest variable in a kitchen extension project. A standard Howdens or Benchmarx kitchen with laminate worktops and standard appliances can cost £8,000-£18,000 all-in. A bespoke English-made kitchen with granite or quartz worktops and Miele or Gaggenau appliances can cost £40,000-£80,000+. Building Control and professional fees: Building Control application fee (full plans application, typical rear extension): £400-£900. Structural engineer (foundation and beam design): £800-£2,000. Architect or designer (drawings for planning, Building Control, and construction): £2,000-£6,000 for a typical rear extension. Party wall surveyor (where a party wall notice is required — e.g., for foundations within 3m of the party wall): £700-£2,500 for a simple agreed award.

A well-designed kitchen extension is typically one of the best-value home improvements for a London property in terms of added market value relative to the cost of the works. For a typical inner London Victorian or Edwardian terrace or semi-detached property (2025 market values): A rear extension that adds an open-plan kitchen, dining, and family living room (20-35 sq m) adds approximately £80,000-£150,000 to the market value of the property in inner London. The extension cost (£55,000-£120,000 for a standard to mid-upper specification project) therefore produces a net value uplift of approximately £0 to £60,000. In terms of percentage return on cost: in inner London (where property values are highest), the percentage value uplift from a kitchen extension is typically 100-130% of the construction cost — meaning that for every £100,000 spent on a kitchen extension, the property typically increases in value by £100,000-£130,000. In outer London (where property values are lower), the percentage uplift is typically 80-110% of construction cost. The financial case for a kitchen extension in London is therefore strong, particularly for long-term owner-occupiers who will benefit from the improved space for several years before any eventual sale. For investment purposes: the capital value uplift from a quality kitchen extension typically takes 3-7 years to fully be reflected in market conditions for a specific property — the extension must be well-designed and well-specified to maximise market value uplift.