Planning and Designing a Kitchen Extension in London: A Step-by-Step Guide

**Starting with the brief — what do you actually want from this space?**

Before approaching an architect or contractor, it is worth being clear about what you want the extended kitchen space to actually do:

• *Functions to plan for*:
• •Cooking: hob position (island? against wall? range cooker?), oven positions, extraction type and route
• •Dining: number of people to seat at an island, a dining table, or both
• •Socialising: open-plan connection to the garden; space for children to be visible from the kitchen
• •Utility: washing machine and dishwasher positions; larder storage; pantry
• •Study or homework area: desk or island seating as secondary function
• •Garden connection: bi-fold or sliding doors; level threshold to patio

**Layout options for a London rear kitchen extension**:

• *1. Simple rear extension (single storey)*:
• The most common type: extends the house straight back into the garden. For a typical London Victorian two-storey terrace (4–5m wide), a rear extension can be:
• •3m depth × full-width (under PD): approximately 12–17m² extension floor area — limited in a full-width context but useful for a galley-style or L-shaped kitchen addition
• •4m depth × full-width (requiring planning permission beyond PD in most boroughs): approximately 16–22m² extension
• •5–6m depth × full-width (planning permission always required): approximately 20–30m²

The structural opening from the existing kitchen into the new extension is typically the full width of the rear wall (or close to it) — this is the defining feature of the open-plan rear kitchen extension.

• *2. Side return infill extension*:
• Many London Victorian and Edwardian terraces have a narrow side return passage — typically 1–2m wide — running along the side of the house to the rear. Building into this side return adds width to the rear kitchen and can create an L-shaped plan:
• •Side return extensions add typically 10–20m² of floor area
• •The side return roof is usually a flat roof at a lower level than the main extension roof (or a glazed roof)
• •The combined rear + side return extension ('wrap-around') can create a much larger open-plan kitchen-diner

• *3. Wrap-around extension (rear + side return)*:
• The most transformative option for London Victorian terraces: a single-storey extension extending both into the side return and the rear garden simultaneously, typically creating an L-shaped or rectangular footprint:
• •Typical size: 25–45m² of new floor area
• •Creates a large open-plan kitchen-diner with multiple room uses
• •Always requires planning permission (exceeds PD limits in combination)
• •Costs typically £65,000–£110,000 (see `extension-cost-london`)

**What size kitchen extension works in a typical London Victorian terrace?**

• For a 4.5m-wide Victorian two-storey terrace (a very common London property type):
• •A 3m deep × 4.5m wide rear extension adds approximately 13.5m² (within PD in most boroughs for single-storey)
• •A 4m deep × 4.5m wide rear extension adds approximately 18m² (planning permission needed in most London boroughs)
• •Adding a 1.5m side return to a 4m rear extension creates approximately 24m² of new floor area (wrap-around, always planning permission)

For most London families, the wrap-around or 4m-deep rear extension produces the most useful kitchen-diner space — a 3m deep extension on a typical terrace feels limited once the kitchen is installed.

**Rooflight and glazing considerations for kitchen extensions**:

One of the defining features of a successful London kitchen extension is the quality of natural light. Key decisions:

• *Rooflights in a flat roof extension*:
• •One or two large rooflights (typically 1.5–3.0m × 0.7–1.0m or a bespoke size) in the flat roof dramatically increase daylight
• •Rooflight specification: Velux Modular Skylights, Glazing Vision, or similar — triple-glazed for Part L compliance (U-value ≤ 1.80 W/m²K for rooflights as per Part L)
• •Roof pitch: flat roof extensions have maximum falls of approximately 7°; roof windows require specific manufacturers' minimum pitches
• •25% glazing limit: Building Regulations Part L limits total glazed area (windows + rooflights + doors) to 25% of the new floor area for extensions, unless a SAP calculation demonstrates the glazing is energy-efficient (which it typically can be with triple-glazed rooflights and bi-fold doors)

• *Bi-fold or sliding doors to garden*:
• •The dominant opening to the rear garden in most London kitchen extensions
• •Bi-fold doors fold back against the walls — maximum open width; requires clear floor space at either end when open
• •Sliding doors (aluminium lift-and-slide or inline sliding) — no floor space required when open; better suited to smaller extensions
• •Level threshold (Part M accessible design requirement): the internal floor level and the external patio level must be coordinated — the level threshold channel drain detail is important (see `extension-utilities-guide`)
• •Minimum structural opening width for comfortable bi-fold doors: 2.4m (two-panel); 2.8m+ (three-panel)

*Fixed glazing over the return (rooflights or structural glass)*: Where a side return extension has a low flat roof, a full-width rooflight over the side return creates a light-well effect — bringing natural light deep into the plan.

**Is planning permission needed for a kitchen extension in London?**

Many rear kitchen extensions in London are built under permitted development (PD) rights — without needing a formal planning application. The PD limits for householder extensions in England are:

• *Single-storey rear extension PD limits*:
• •Detached house: maximum 8m depth from the original rear wall
• •Semi-detached or terraced house: maximum 6m depth from the original rear wall
• •Maximum height: 4m (or 3m if within 2m of a boundary)
• •Materials: must be similar in appearance to the existing house

*IMPORTANT — London-specific complications that often remove or restrict PD rights*:

1. *Conservation areas*: In a conservation area, cladding the rear elevation, extending beyond the rear wall line of the side elevation (visible from the highway), or adding large glazing to a traditionally designed property may all require planning permission even if the size is within PD limits. Side extensions in conservation areas ALWAYS need planning permission (PD side extension rights are removed in conservation areas). Check your borough's conservation area designation.

2. *Article 4 Directions*: Some London boroughs have Article 4 Directions that remove permitted development rights in specific areas — including rear extensions and associated glazing changes. Common in Islington, Hackney, Camden, Kensington and Chelsea, and Westminster.

3. *Flats and maisonettes*: PD rights do not apply to flats and maisonettes (or to houses that have been converted into flats). Extensions to flats always need planning permission.

4. *Larger home extension scheme*: For rear extensions between 4m–6m (terraced/semi) or 4m–8m (detached), the Prior Approval (Larger Home Extension) scheme applies — you must notify the council, which consults neighbours, and if neighbours object the council must assess the impact. This is NOT the same as full planning permission but is a required notification process.

5. *Previous extensions*: If the property has already had extensions built under PD rights (even by a previous owner), the allowance is cumulative and the available PD depth may have been partly used.

**Applying for planning permission for a kitchen extension in London**:

• Where planning permission is needed:
• •Application fee: £258 for a householder application (2025)
• •Required drawings: site location plan, block plan, existing and proposed floor plans and elevations (see `planning-application-drawings-guide`)
• •Decision period: statutory 8 weeks (standard) or 13 weeks (where an Environmental Impact Assessment is required — rare for residential householder applications)
• •Pre-application advice: for conservation area extensions or any extension where the planning position is uncertain, use pre-application advice (see `pre-application-advice-guide`)

**Building Regulations requirements for a London kitchen extension**:

Regardless of whether planning permission is needed, all structural extensions require Building Regulations approval. The main compliance areas for a kitchen extension:

*Part A (Structure)*: Foundation design and structural beam to SE's calculations

*Part B (Fire safety)*: Smoke alarms; fire doors where required (kitchen-to-hallway connection in a two-storey house); escape route from upper floors not blocked

*Part C (Moisture)*: DPC at 150mm minimum; DPM in floor; cavity closers at jambs and heads; drainage management

*Part E (Acoustics)*: Where the extension is attached to another property, wall construction must meet minimum airborne sound insulation requirements (Rw ≥ 40dB for walls between dwellings)

*Part F (Ventilation)*: Kitchen extract fan at minimum 60 l/s (intermittent extraction) or 13 l/s (continuous extract system); trickle ventilators in all new windows and doors

*Part H (Drainage)*: All new drainage compliant with Part H; drainage plan to be approved

*Part L (Energy efficiency)*: All new thermal elements to meet backstop U-values; any new windows/rooflights/bi-fold doors not to increase heat loss beyond Part L limits; total glazed area not to exceed 25% of new floor area unless SAP demonstrates compliance

*Part M (Access)*: Level threshold to bi-fold doors; minimum door widths

*Part P (Electrical)*: All new electrical work by NICEIC or NAPIT registered electrician; EIC certificate on completion

*Part S (EV charging)*: Where extension triggers planning permission and property has parking, EV charging infrastructure required

**Party wall considerations for kitchen extensions in London**:

• If the kitchen extension is built up to or along the boundary with a neighbouring property (as is almost always the case for a side return extension, and often for rear extensions that run to the rear of a terrace), the Party Wall etc. Act 1996 may apply:
• •Building a new wall on or along the boundary (line of junction) triggers the Act
• •Excavating within 3m of a neighbouring structure (foundation of the extension near a party wall) triggers the Act
• •The Act requires serving notice on affected neighbours (2 months' notice for party wall works; 1 month for excavations)
• •If the neighbour does not consent within 14 days, a party wall surveyor must be appointed
• •Cost: party wall surveyor fees typically £800–£2,000 per neighbouring property affected (see `party-wall-act-guide`)

**Kitchen extension costs in London (2025 indicative)**:

Kitchen extension costs in London depend heavily on size, specification level, and whether a wrap-around or simple rear extension is chosen. The following figures are indicative:

| Extension type | Indicative cost (construction only, client-supplied kitchen) | |---|---| | Simple rear extension 3m × 4m (12m²) | £35,000 – £52,000 | | Standard rear extension 4m × full width (18–20m²) | £45,000 – £70,000 | | Wrap-around (rear + side return, ~25–35m²) | £65,000 – £110,000 | | Double-storey rear (ground floor kitchen + upper bedroom) | £80,000 – £130,000 |

*Note*: Kitchen furniture, appliances, and floor finishes are typically client-supplied in RCB's standard contracts and are excluded from the above figures. A mid-range kitchen (units, appliances, worktops) adds £10,000–£35,000 depending on specification. Floor tiles and fitting add £3,000–£8,000.

**What affects the cost of a London kitchen extension**:

• •*Size and shape*: Larger extensions cost more — but the cost per m² typically falls as size increases (fixed costs are spread over more floor area)
• •*Structural opening size*: Larger steel beams and more complex propping arrangements cost more
• •*Roof type*: Flat roofs are generally cheaper than pitched; glazed roofs are premium
• •*Glazing specification*: Large bi-fold or sliding door systems (especially aluminium) are significant cost items — typically £4,000–£12,000 per set
• •*Rooflights*: Large structural rooflights add £1,500–£6,000 per unit
• •*Ground conditions*: Where piled foundations are needed (near trees, in poor ground, near basements), foundation costs increase significantly
• •*Party wall*: Neighbouring party wall surveys add professional fees
• •*Design costs*: Architect's fees (planning + Building Regulations) typically £3,000–£8,000 for a kitchen extension project

**Programme for a London kitchen extension**:

• A typical London rear kitchen extension (15–25m², structural opening, flat roof, bi-fold doors):
• •Pre-construction (planning, Building Regs, procurement): 3–6 months
• •Construction on site: 10–16 weeks
• •Total from first conversation to completed kitchen: 6–12 months (depending on planning authority processing times)

**What to look for when choosing a contractor for your kitchen extension**:

When choosing a contractor for a London kitchen extension, the key questions to ask are:

1. *Principal contractor capability*: Can they coordinate all trades in sequence (structural, drainage, electrical, plumbing, plastering, carpentry, kitchen installation) under one roof, or will you need to manage multiple contractors yourself?

2. *Building Regulations experience*: Have they done full Building Regulations applications and dealt with Building Control inspections before? Can they provide completion certificates?

3. *Party wall experience*: Have they worked with party wall agreements before? Do they understand the timing requirements for party wall notices?

4. *Kitchen installation coordination*: Do they work with your kitchen designer (or supply and install the kitchen), or do you need to separately manage the kitchen installer alongside the building contractor?

5. *Structural engineer*: Do they have a preferred SE, or do you appoint independently?

6. *References*: Can they provide references from previous kitchen extension clients in London — specifically from clients whose projects have been completed for at least 6 months, so any defects period issues are known?

RCB Design & Build handles all of the above under one principal contractor appointment — from planning support through Building Regulations, structural engineering coordination, party wall, drainage, M&E, plastering, carpentry, and kitchen installation coordination.