Kitchen Extension — The Complete Design and Build Guide for London Homeowners

A kitchen extension is a rear extension to a house that creates additional floor space, combined with either the relocation of the kitchen into the new space or the expansion of an existing kitchen layout. In most London terraced houses, it creates an open-plan kitchen-dining-living area across the full width of the rear of the house.

• The typical project involves:
• •A single-storey rear extension (3–6 metres deep, 4–6 metres wide)
• •A structural opening between the existing house and the new extension
• •Relocation of the kitchen into the back of the new space
• •A dining area and/or living/family room area in the front part of the new space
• •Full-width glazed rear elevation (bifold doors, sliding doors, or French doors with flanking windows)
• •New kitchen installation
• •Structural works to connect old and new

The result is a ground floor that feels like one connected space from front to back — very different from the original house, which typically has a narrow kitchen at the back, a separate dining room in the middle, and a sitting room at the front.

Kitchen extension costs in London (2025) depend heavily on the size, specification, and whether the kitchen itself is included:

• **Extension build only (no kitchen):**
• •3m × 4m single-storey rear: £40,000–£60,000
• •5m × 5m single-storey rear: £55,000–£80,000
• •Side return + rear (wrap-around): £65,000–£100,000

• **Extension build with kitchen installation:**
• •4m × 5m with mid-range kitchen: £65,000–£90,000
• •5m × 6m with premium kitchen: £90,000–£130,000
• •Wrap-around with premium kitchen and lantern: £100,000–£150,000+

• **Key cost variables:**
• •**Kitchen specification**: the kitchen units themselves can range from £8,000–£40,000+ depending on brand and quality. RCB installs client-supplied kitchens as standard.
• •**Glazed rear elevation**: full-width bifold doors (£5,000–£12,000) or aluminium sliding doors (£6,000–£15,000) are a significant cost item
• •**Glazed roof lantern or roof lights**: structural glass lantern (£8,000–£20,000) vs. standard EPDM flat roof (included in base cost)
• •**Structural opening**: removing the wall between the existing house and the extension and installing a steel beam costs £4,000–£7,000
• •**Kitchen relocation**: if the existing kitchen plumbing and gas supply need to be moved to the new location, budget £2,000–£4,000 extra
• •**Underfloor heating**: over the new concrete slab, water UFH costs £2,500–£5,000 for the system
• •**External landscaping**: decking or paving to the rear garden (if included) costs £3,000–£8,000+

The planning rules for a kitchen extension are the same as for any single-storey rear extension.

• **Permitted Development (most common)**:
• Most single-storey rear extensions on terraced and semi-detached houses are Permitted Development:
• •Up to 4 metres deep: standard Permitted Development (no planning application needed)
• •Up to 6 metres deep: Prior Approval scheme (Neighbour Consultation Scheme — you notify the council, they consult neighbours, 42-day process)
• •Detached houses: up to 8 metres standard PD, same under Prior Approval

• **Full planning permission required when:**
• •The extension exceeds the PD/Prior Approval depth limits
• •The property is in a Conservation Area and the extension would be visible from the street
• •The property is listed
• •The property is a flat
• •An Article 4 Direction applies

• **Other approvals needed regardless of planning status:**
• •Building Regulations: always required. New extension structure, drainage, electrical works, and structural openings all need Building Control notification and inspections
• •Party Wall: almost certain to be required for a rear extension on a terraced house — excavations for foundations will be within 3 metres of the adjoining property

For a standard 4–5 metre deep kitchen extension on a non-Conservation Area terraced house in London, the planning route is typically: 1. Prior Approval application (if over 4m) or LDC (to confirm PD status) 2. Building Regulations — Full Plans application 3. Party Wall notice (served in parallel with planning)

The kitchen extension creates more square footage than almost any other project for a terraced house — but whether the new space works brilliantly or just adequately depends on the design decisions made early.

**Kitchen placement and flow** The most common successful layout puts the kitchen along the back or one side of the new space, with a dining island or breakfast bar creating a transition to the dining area, and the dining space flowing into a seating or family area. The key principle: the kitchen should face the garden, with the cook looking out rather than at a wall.

**Natural light** A deep rear extension can create a dark zone in the middle of the house (between the existing front rooms and the new rear extension). Solutions: roof lantern or glazed roof section over part of the extension, skylights in the flat roof, or a large rear glazed wall that floods the space with afternoon and evening light.

**Connection to the garden** Full-width bifold or sliding doors to the rear garden are the defining feature of most London kitchen extensions. They transform the relationship between interior and exterior. The decision is width (how many panels), threshold (level access vs. a low step), and material (aluminium is standard for quality and thermal performance).

**The structural opening** The structural opening from the existing house into the extension determines how connected the old and new spaces feel. A full-width opening (typically 3–4 metres, the full width of the room) with the minimum structural column depth creates the most open feel. A narrower opening (single doorway) creates a more defined separation between rooms. Most clients opt for the widest opening the structure allows.

**Underfloor heating or radiators?** Underfloor heating suits kitchen extensions well — it works with hard floors (tile, stone, engineered wood) and creates an even heat that suits the open-plan space. A single radiator in a large open-plan kitchen-dining room is rarely adequate. If the floor is a new concrete slab, installing water UFH pipes now is significantly cheaper than retrofitting later.

A typical kitchen extension with kitchen relocation in a London terraced house takes 12–16 weeks on site.

**Weeks 1–2: Strip-out and preparation** Demolition of the existing rear wall, removal of the old kitchen if it is in the area to be extended. Scaffold erected. Enabling works.

**Weeks 2–4: Excavations and foundations** Strip foundations (or deeper if ground conditions require) excavated and poured. Drainage rerouted or extended to the new position.

**Weeks 3–5: Concrete slab and walls** Concrete ground slab poured. External walls of the new extension built (blockwork or timber frame). Structural steel beams installed where the new extension connects to the original house.

**Weeks 5–7: Roof** Roof structure built. Flat roof covering installed (EPDM rubber or GRP). Roof lantern or skylights installed if specified. This is the critical path — once the roof is watertight, all internal works can proceed.

**Weeks 6–9: First-fix services and insulation** Electrical first fix. Kitchen plumbing rerouted to new position. Underfloor heating pipes laid and screed poured. Insulation to walls and roof.

**Weeks 8–12: Internal finishes** Plastering. Second-fix electrics. Second-fix plumbing. Kitchen installation (units, worktops, appliances). Splashback tiling.

**Weeks 11–15: Completion** Bifold/sliding door installation. Flooring throughout the new space. Decoration. Snagging. Building Control final inspection and completion certificate.