Kitchen Islands for London Home Extensions: Design, Size, and What to Consider

The most common mistake with kitchen islands in London home extensions is making the island too large for the available space. The result is a beautiful piece of joinery surrounded by insufficient circulation space that makes the kitchen uncomfortable to use — particularly when two people are cooking simultaneously or when guests are standing at the island while the cook is working. The fundamental sizing rule: the minimum clear distance between the face of the island and any facing run of kitchen units, appliances, or walls should be 1,000mm. This allows one person to stand in front of a low-level oven or open a dishwasher without being physically blocked. 1,200mm is the recommended dimension for comfortable two-cook use, and 1,400mm is ideal. In a kitchen extension of 4 metres in internal width (a fairly typical width for a London terraced house rear extension), an island of 1,200mm width leaves 1,400mm on one side and leaves 1,400mm on the other — only achievable if the kitchen units are very narrow or the island sits very centrally. In practice, a 4-metre-wide kitchen comfortably accommodates an island of 800-1,000mm width. A kitchen extension of 5-6 metres width can accommodate a 1,200-1,500mm island with comfortable circulation on both sides. For a typical London rear extension of 4-5 metres width, the island width is often constrained to 900-1,100mm rather than the 1,200-1,500mm that clients initially have in mind.

Island length (the dimension running parallel to the main kitchen run) is typically less constrained than island width. The minimum useful island length for cooking purposes is approximately 1,200mm — enough for a 600mm hob with preparation space on each side. A length of 1,500-2,000mm is comfortable for a combined preparation and cooking island. Beyond 2,400mm, an island starts to dominate the room and may interrupt natural traffic flow through the kitchen. Islands intended for seating require additional length: each seated person needs approximately 600mm of linear worktop space. Adding two bar stools to a cooking island therefore requires at least 1,200mm of seating overhang length. A combined cooking and seating island of 2,200-2,400mm length (with hob at one end, seating at the other) is achievable in a kitchen extension of 5-6 metres length. The island should be proportional to the room: in a 3.5-metre-long kitchen, a 2.4-metre island leaves only 550mm of circulation at each end — too little. The end circulation clearance should be a minimum of 900mm, preferably 1,000mm.

Incorporating a sink or hob in a kitchen island has implications that must be planned before the floor slab or screed is poured — after which point they become significantly more expensive or disruptive to add. Sink drainage: draining a sink in the centre of the kitchen (rather than against the wall, where drainage runs back through the wall cavity) requires a drainage pipe to run either: under the floor slab to the nearest drainage point (typically the kitchen drain in the existing floor plan area); or within a raised floor section beneath the island (a raised plinth arrangement that accommodates the drainage fall without running under the slab). Both approaches are achievable, but both must be incorporated into the drainage design before the concrete floor is poured. Retrofitting drainage for an island sink in an existing screed floor requires breaking up the floor and relevelling — expensive. Water supply: a cold water supply and a hot water supply to the island sink must be run through the floor in coordination with the drainage design. Electrical for hob: a kitchen island hob requires a 32-amp or 45-amp electrical circuit (depending on the hob type). This circuit must be run to the island position before the floor is finished. For an induction hob (which requires a larger electrical load than gas), the circuit should be run in cable sized for the full hob load. USB/data: increasingly, clients request USB charging points and data connections in the island worktop. These low-voltage circuits can be added after the floor is finished (surface-run or chased) more easily than power circuits, but are cleaner if planned from the outset.

Positioning a hob on a kitchen island creates an extraction challenge: the conventional wall-mounted extractor hood cannot be used because there is no wall above the hob. The extraction options for an island hob are: Ceiling-mounted extractor hood (island hood): a canopy-style extractor suspended from the ceiling above the island hob, ducted through the ceiling void and up through the roof or out through the rear wall to the exterior. Island hoods range from £400 (entry-level) to £3,000+ (high-end designer models with integrated lighting). Extraction performance is measured in m³/hour — for a domestic kitchen island, a minimum of 600-800 m³/hour is recommended, with 1,000 m³/hour or more for heavy cooking. Downdraft extractor: a unit that rises from the worktop surface behind the hob (or from within the hob frame in integrated models) and draws cooking fumes downward rather than upward. Downdraft extraction requires the extracted air to be ducted through the floor and away from the building, which again requires a duct chase to be planned before the floor is poured. Performance of downdraft extractors has improved significantly but they remain less effective than ceiling-mounted hoods for high-heat cooking. Recirculating ceiling-mounted hood: an island hood that filters and recirculates the extracted air rather than ducting it to the exterior. This avoids the need for external ducting but requires regular filter replacement and is significantly less effective at removing moisture and cooking odours than a ducted system. For best results with an island hob, a ducted ceiling-mounted island hood is the recommended specification.

Kitchen islands are available in two broad categories: Freestanding island units (purchased as furniture, not fixed joinery): available from kitchen and furniture retailers at price points from £300 (basic butcher block on legs) to £3,000-£5,000 (substantial painted or solid wood freestanding units). Freestanding islands cannot be plumbed for a sink or hob without significant adaptation; they are primarily useful for additional preparation surface and storage. A freestanding island can be moved if the layout needs to change, which is an advantage in rental properties or where flexibility is valued. Fitted bespoke or semi-bespoke island (integral to the kitchen fit-out): a fixed island is integrated into the kitchen cabinetry design, using the same door style and materials as the rest of the kitchen. It provides solid structural support for a sink, hob, and heavy worktop materials (stone, porcelain). Storage within a fitted island can incorporate: deep pan drawers (the most useful low-level storage in a kitchen); wine racks or wine fridges; recycling and waste management; electrical appliance garages with retractable doors; or charging drawers. Cost of a fitted kitchen island (cabinetry only, excluding worktop, sink, and appliances) in a mid-range London kitchen: £2,000-£6,000 for a standard semi-bespoke kitchen. £6,000-£15,000+ for a bespoke handmade island with custom features. A large statement island in a high-specification London kitchen extension, with bespoke joinery, a feature lighting pendant, a stone waterfall worktop, and integrated sink, can cost £15,000-£30,000 for the island element alone.