Kitchen Extension London: What It Costs, What It Involves, and Is It Worth It?

Most London Victorian and Edwardian terraces have the same layout: a narrow kitchen at the rear of the property, accessed through a back reception room, with a small outbuilding or lean-to beyond. The kitchen is dark, disconnected from the garden, and too small for a family to use comfortably.

• A rear kitchen extension changes this completely. By removing the rear wall, demolishing the outbuilding, and extending out into the garden, the kitchen can become:
• •An open-plan kitchen-dining space large enough for a dining table, island, and cooking area
• •Connected directly to the garden via bifold or sliding doors
• •Well-lit from above via a roof lantern or glazed roof section
• •Integrated with a utility room, snug, or additional reception space

Estate agents consistently report that this type of project — open-plan kitchen-diner extension — is the single highest-impact project for family home value in London. It changes both how the house feels to live in and how it presents to buyers.

Most single-storey kitchen extensions in London are permitted development, subject to size limits:

• •Maximum 4m depth from the rear wall (detached house) or 3m depth (semi-detached or terraced house) without planning permission
• •Height must not exceed 4m at the ridge or 3m at the eaves
• •The extension must not cover more than 50% of the total garden area

Larger Home Extension Scheme (prior approval): since May 2019, it has been possible to extend up to 8m depth (detached) or 6m depth (semi/terrace) under a prior approval process — not a full planning application, but a 42-day notification period during which neighbours can raise concerns. This is useful where the standard permitted development limits are too restrictive for the desired kitchen size.

Conservation areas: in a conservation area, permitted development rights for rear extensions may be restricted. Check with your local authority before assuming PD applies.

Planning permission: required when the extension exceeds PD limits, is in a conservation area or Article 4 zone, or involves other changes (upper floor, changes to the front elevation). Planning applications for kitchen extensions in London typically take 8–13 weeks.

The single most important structural element in a kitchen extension is the opening between the existing house and the new extension. In a Victorian or Edwardian terrace, the rear wall of the property is load-bearing — it carries the floor above and potentially the roof structure. Removing all or part of this wall requires a structural steel beam.

The process: 1. A structural engineer designs the steel beam (size, bearing details, padstones) 2. The existing wall is temporarily propped with acrow props and needles 3. The wall is carefully removed within the prop line 4. Padstones are cast or set in the piers remaining on each side 5. The steel beam is lifted and installed on the padstones 6. The props are removed 7. The steel is fire-protected and the opening is finished

• Cost of a structural opening in a London terrace:
• •3m wide opening: £5,000–£8,000 (steel, labour, temporary propping, making good)
• •4m wide opening: £7,000–£11,000
• •Full-width opening (5m+): £9,000–£15,000

This cost is frequently underestimated or buried in a vague 'structural works' line in a contractor's quote. Always ask for this to be itemised — it is one of the largest single cost elements in a kitchen extension.

The quality of the structural opening also affects everything that follows. A poorly executed opening — insufficient bearing length, inadequate padstones, twisted steel — will cause settlement cracks, sticking doors, and structural problems years later. This is not an area to cut costs.

The roof of a kitchen extension significantly affects the light, atmosphere, and cost of the space. Main options:

Flat roof with EPDM membrane: the most common and most cost-effective. Creates maximum internal ceiling height. Allows for a roof lantern to be added without changing the roof structure. Modern EPDM single-ply membranes have a 25-year warranty and are very reliable when correctly installed. Cost: included in standard extension price.

Roof lantern: a glazed lantern (typically 1.0m x 1.5m or larger) set into a flat roof brings natural light into the centre of a deep extension that might otherwise be dark. This is probably the single most impactful £3,000 you can spend on a kitchen extension — the quality of light changes dramatically. Cost: £2,500–£6,000 for a standard powder-coated aluminium lantern, plus installation.

Full-width glazed roof: sliding or fixed structural glazing across the full width of the extension. Creates a strong architectural statement and exceptional light levels. Requires solar control glazing to prevent overheating. Cost: £8,000–£25,000+ for the glazed system.

Pitched tiled roof: more traditional in appearance, often required in conservation areas or where PD conditions require it to match the existing house. Adds 3–4 weeks to the programme and £4,000–£9,000 versus flat. Reduces internal ceiling height at the rear of the extension.

Walk-on glass or decking above: where an upper floor room opens onto the extension roof and access is desired, a walk-on roof system can be specified. Adds significant cost and complexity — budget £8,000–£18,000 additional.

Bifold or sliding doors connecting the kitchen extension to the garden are the single most-desired feature in a London kitchen extension project. They are also one of the most variable cost items.

• Bifold doors: fold back in sections to create a full-width opening to the garden. The most popular specification. Cost breakdown:
• •3-panel timber bifold (budget): £2,500–£4,000 supply only
• •3-panel aluminium bifold (standard): £3,500–£6,000 supply and install
• •4-panel aluminium bifold: £5,000–£8,000 supply and install
• •5-panel aluminium bifold: £6,500–£10,000 supply and install
• •Premium German-engineered bifolding system (Schuco, WERU): £10,000–£18,000

Sliding doors: slide on a track rather than folding. Can span wider openings than bifolding. Less 'open plan' feel — a portion of the frame is always in the sightline. Growing in popularity for contemporary interiors. Similar price range to bifolding for comparable widths.

Fixed glazing plus opening door section: where full bifold is not required (smaller opening, more moderate budget), a large fixed pane with a single casement or French door is effective and significantly cheaper.

Glazing specification: all bifold and sliding doors in a kitchen extension should be double-glazed as a minimum. Triple glazing is worth considering if the extension faces north or east. Solar control glass on south and west-facing extensions reduces overheating risk significantly.

This is where many homeowners underestimate the total project cost. The kitchen extension build (structure, roof, doors, plaster, electrics) is one budget. The kitchen itself is a separate and often equally large budget.

• Kitchen supply and installation cost ranges in London 2025:
• •Budget (IKEA, B&Q, Wickes): £5,000–£12,000 for a medium-sized kitchen, supplied and installed
• •Mid-range (Howdens, Wren, Magnet): £12,000–£28,000
• •Upper-mid (Second Nature, Symphony, Masterclass): £22,000–£45,000
• •High-end bespoke joinery: £40,000–£100,000+

• Appliances (separate from kitchen units):
• •Budget appliance package: £2,000–£5,000
• •Mid-range (Bosch, Siemens, Neff): £5,000–£12,000
• •Premium (Miele, Gaggenau, AEG): £10,000–£25,000+
• •Range cooker (Rangemaster, Falcon, AGA): £3,000–£20,000

Underfloor heating: wet UFH (connected to the boiler) for a 20m² extension floor: £3,000–£5,500 installed. The most comfortable and energy-efficient heating for a kitchen extension.

• A realistic total project budget for a quality kitchen extension in London:
• •Build cost (structure, roof, doors, finishes): £55,000–£85,000
• •Kitchen (mid-range): £18,000–£30,000
• •Appliances: £5,000–£12,000
• •Underfloor heating: £3,500–£5,500
• •**Total: £81,500–£132,500 + VAT**