Kitchen Layout for Extensions and Renovations: What Works and What Doesn't

**1. Galley kitchen**:

*What it is*: Two parallel runs of base and wall units on facing walls, with a single corridor between them.

*When it works well*: Narrow spaces (typically 1.8–3.0m wide) where two-sided layout is the only option; properties where the kitchen is in a passageway or narrow outrigger; when a second person working in the kitchen is rarely needed.

*Minimum dimension*: A functional galley kitchen requires at least 1.0m clear between the two unit runs (ideally 1.2m) — enough for one person to work and for an oven door to open without blocking the passageway.

*When it doesn't work well*: Open-plan extensions where the kitchen is visible from the living and dining areas — a galley layout has a closed, service-corridor feel that conflicts with the sociable character of an open-plan space.

**2. L-shaped kitchen**:

*What it is*: Units on two adjacent walls, forming an 'L'. One run is typically the sink and preparation counter; the other is the hob, oven, and refrigerator.

*When it works well*: Medium-sized rooms (typically 3.0m × 3.5m or larger); open-plan extensions where the kitchen occupies one corner of the open space; when the dining area extends from one arm of the 'L'.

*Working triangle*: The 'kitchen work triangle' (the distance between sink, hob, and refrigerator) is naturally efficient in an L-shaped layout if the three elements are placed one on each arm of the 'L' — the triangle is compact and within a half-turn of movement.

**3. U-shaped kitchen**:

*What it is*: Units on three walls, forming a 'U'. The most work-efficient layout — everything is within arm's reach of a central working position.

*When it works well*: Larger rooms (minimum 3.5m × 3.5m — the open side of the 'U' needs to be at least 1.2m for comfortable movement); dedicated kitchen rooms rather than open-plan; when multiple people cook simultaneously.

*When it doesn't work well*: In an open-plan extension, the third arm of the 'U' often conflicts with the open flow between kitchen and dining/living areas — the visual 'closure' of the third run can make the space feel divided.

**4. Island or peninsula kitchen (open plan)**:

*What it is*: Base units along one or two walls, with a freestanding island (or peninsula — one end fixed to a wall) in the centre of the space. The island typically contains the hob (with extraction above) and/or additional preparation space.

*When it works well*: Large open-plan kitchen-dining-living extensions (typically 30–50m² open plan space); when the kitchen forms the social hub of the home — an island is the most 'sociable' layout, allowing conversation while cooking; when children or guests can sit at the island on bar stools while the cook works.

*The extraction challenge for islands*: A hob on an island requires ceiling-mounted extraction — either a ceiling extractor (hanging from the ceiling above the island) or a downdraft extractor (integrated into the island worktop, drawing vapour down rather than up). Both have implications for the kitchen extension design: ceiling extraction requires ducting through the ceiling or roof structure to an external wall; downdraft extraction requires space within the island structure and a duct to the outside. For an extension with a flat roof, the extraction duct must be designed before the roof structure is fixed — retrofitting extraction ductwork through a finished flat roof is expensive.

**The drainage constraint — why the sink position matters**:

The sink position is determined by the drainage run — the waste pipe from the sink must fall at minimum 1:40 gradient (1cm drop per 40cm horizontal run) to the nearest soil stack or external gully. In a rear extension, the drainage connection point is typically at the rear of the extension or at a side gully — which means the sink should ideally be positioned on the external wall nearest the drainage connection.

*The consequence of a remote sink position*: Placing the sink on a kitchen island or on a wall far from the drainage connection requires a long, low-gradient drainage run below the floor — which is achievable but adds cost (longer pipe run, a deeper or sloped floor void). A rule of thumb: every 1m of horizontal pipe run requires at least 25mm of drop — over 4m horizontal, the pipe drops 100mm. If the floor void is shallow (standard suspended timber floor), a long drainage run may not be achievable without raising the floor level, which has implications for thresholds and headroom.

For a kitchen island with a sink, confirm the drainage route with the contractor or structural engineer before finalising the layout — it is a design decision that interacts with the floor structure.

**The extraction constraint — why the hob position matters**:

• Extraction over the hob (to meet Part F Building Regulations ventilation requirements and to keep the kitchen functional) requires either:
• •A wall-mounted canopy extractor: the hob is on a wall run, the extractor is mounted on the wall above the hob, and the duct exits through the wall or a cabinet to outside
• •A ceiling-mounted island extractor: the hob is on an island, the extractor hangs from the ceiling above, and the duct runs through the ceiling structure to an external wall or through a concealed route in the roof
• •A downdraft extractor: the duct exits through the floor or island structure to outside

The extraction route must be planned before the walls and roof are built — particularly for extensions with flat roofs or where the extraction duct must pass through structural elements.

**Part F ventilation minimum standard**:

• •Kitchen extract must achieve 60 l/s during cooking (cooker hood) or 30 l/s continuous extract
• •The extract must be ducted to outside — recirculation filters are not Part F compliant (they clean the air but do not remove moisture)
• •Trickle ventilation (a trickle vent in the kitchen window) provides background ventilation independent of extract

**Structural constraints — walls to be removed and the beam position**:

For open-plan kitchen-dining-living extensions, the removal of the existing rear wall and possibly internal walls creates a large structural beam overhead — the steel lintel (RSJ) spanning the opening between the existing house and the extension. The beam position and depth affects the ceiling height at the junction and the design of any bifold or sliding door. The beam must be specified by the structural engineer before the kitchen layout is finalised — the beam depth dictates the ceiling height at the threshold, which affects worktop heights and pendant light positions in the kitchen adjacent to the junction.

**Mistake 1: Placing the dishwasher far from the sink**:

Dishwashers require hot and cold supply, a 13A socket, and a waste pipe to the same drain as the sink. Placing the dishwasher more than 300mm from the sink creates a long waste pipe run inside the unit cabinet — awkward to install and prone to blockage. The dishwasher should be placed immediately adjacent to the sink (ideally on the left if the user is right-handed, so clean items can be taken to a drying area to the right).

**Mistake 2: Specifying an extraction system after the roof is built**:

As described above, an island hob or a hob on a wall without an adjacent external wall requires a planned extraction route. Many extension kitchen layouts are designed with an island hob without considering how the extraction duct reaches outside — and the solution (a bulkhead in the ceiling, an external duct box, or a downdraft unit) that is required after the roof is built is more expensive and less attractive than one designed in.

**Mistake 3: Under-specifying worktop depth at the hob**:

Standard worktop depth is 600mm (matching standard base unit depth). If the hob is a 90cm wide 5-burner unit (common in London extension kitchens), the worktop on each side of the hob should be at least 300mm wide to allow pan handling space. Design the worktop run and unit layout with the actual hob size in mind, not a standard 60cm hob position.

**Mistake 4: Ignoring the relationship between kitchen worktop height and window sill**:

In an extension with windows above the sink or along the wall runs, the window sill height relative to the worktop height is critical. Standard worktop height is 900mm from finished floor level. If the architect has specified 900mm window sills (to provide privacy or security), the window sill will sit flush with the worktop — making the window inoperable and the reveal unusable. Window sill heights in a kitchen extension should be confirmed against the worktop height and ideally be 1,000–1,200mm from floor level if privacy allows, allowing a tiled splashback between worktop and window sill.

**Mistake 5: Open-plan kitchen with no acoustic separation**:

In a full open-plan kitchen-dining-living space, the kitchen extraction noise, appliance noise, and cooking smells are shared with the living and dining areas. For many clients this is a desired feature of open-plan living — but for others, the noise and smell during cooking is a nuisance. Consider: semi-open plan with a pocket door or sliding panel that can close off the kitchen when not in use; acoustic-rated extraction; or a separate utility room for washing machine, tumble dryer, and secondary prep that limits noise and laundry activity in the main open space.