Question 1

How much does a kitchen extension cost in London?

Accepted Answer

A kitchen extension in Greater London typically costs £70,000-£120,000 for a single-storey rear extension (20-30m2) including the shell structure, services, decoration and flooring but excluding the kitchen units and appliances (client-supplied). The kitchen fit-out itself (units, worktops, appliances) typically adds £10,000-£40,000 depending on specification. Budget, mid-range and premium kitchen brands range from £5,000 (flat-pack) to £25,000+ (handleless German kitchens from brands like Nobilia, Schuller or Hacker).

Question 2

What size kitchen extension do I need for an island?

Accepted Answer

To accommodate a kitchen island with comfortable circulation, you need a minimum internal width of 3.6m and a minimum clearance of 900mm (ideally 1,100mm) around all sides of the island. A practical island is typically 1,200mm x 600mm minimum. For an island with seating on one side, add 300mm depth for an overhang and allow 600mm per stool. This means the extension should be at least 4.5m wide internally if the kitchen runs along one wall with an island in the centre. A side return infill combined with a rear extension is the most common way to achieve this width.

Question 3

Should I choose bi-fold doors or sliding doors?

Accepted Answer

Bi-fold doors fold and stack to one side, creating a near-full opening (typically 90% of the aperture is clear). They cost £3,000-£8,000 for a 3-4m span in aluminium. Sliding doors (inline sliders) have one or more panels that slide behind a fixed panel, so only 50-66% of the opening is clear, but they are more airtight (better U-values), require less space to operate and have a cleaner aesthetic. Slim-frame sliding systems like Reynaers CP 155 cost £4,000-£10,000. For maximum opening to the garden, bi-folds win. For thermal performance and contemporary aesthetics, sliders are increasingly preferred.

Question 4

Do I need planning permission for a kitchen extension?

Accepted Answer

A single-storey rear kitchen extension up to 6m deep (terraced/semi) or 8m deep (detached) is usually covered by Permitted Development under the Neighbour Consultation Scheme. You must apply for Prior Approval through your local council (8-week process, typically £96 fee). If the extension exceeds these limits, is in a conservation area, or involves a side extension, you may need full planning permission (13-week decision period, £258 fee for a householder application). RCB handles all planning applications and provides a pre-application feasibility assessment at the initial site visit.

Question 5

What flooring works best in a kitchen extension?

Accepted Answer

Popular options include: (1) Large-format porcelain tiles (600x600mm or 600x1200mm) - durable, waterproof, easy to maintain, work well with underfloor heating (£40-£100/m2 supply, £40-£60/m2 install); (2) Polished concrete or micro-cement screed - industrial aesthetic, seamless, works with UFH (£80-£150/m2); (3) Engineered wood - warm underfoot, works with UFH if under 15mm thick (£40-£80/m2 supply); (4) Luxury vinyl tile (LVT) - waterproof, soft underfoot, many designs (£25-£50/m2). Laminate is our standard specification. Carpet is not installed by RCB. Note: ceramic tiles must be 300x300mm minimum per our standard specification.

Question 6

Should I install underfloor heating in a kitchen extension?

Accepted Answer

We strongly recommend underfloor heating (UFH) in kitchen extensions, particularly with tiled or stone floors which are cold underfoot without it. Wet UFH systems (connected to your boiler or heat pump) cost £50-£80/m2 to install in a new extension and run approximately 15-20% more efficiently than radiators because they operate at lower water temperatures. Electric UFH mats cost £30-£50/m2 but are more expensive to run. UFH must be installed before the screed is poured, so it needs to be decided early in the project. The screed takes 21-28 days to cure before tiling can begin.

Question 7

What utilities need to be moved for a kitchen extension?

Accepted Answer

Common utility relocations include: (1) Drainage - the soil pipe and waste runs may need rerouting if the extension covers the existing manhole or drain run (£1,500-£4,000); (2) Gas meter - if the meter is on the rear wall it must be relocated (contact your gas supplier, typically free or low cost but takes 4-6 weeks to arrange); (3) Electrics - the consumer unit may need upgrading and exterior cables/junction boxes relocated; (4) Boiler flue - if the boiler is on the rear wall, the flue must not terminate inside the new extension (either move the boiler or extend the flue). These are identified during the site survey and included in the quotation.

Question 8

How do I design an open-plan kitchen-diner that works?

Accepted Answer

Key principles: (1) Zone the space - use flooring changes, ceiling height drops or pendant lighting to define cooking, dining and living areas; (2) Position the kitchen along one or two walls with the sink facing the garden; (3) Place the island to create a natural barrier between cooking and living zones; (4) Ensure the "working triangle" (sink, hob, fridge) stays compact - no more than 6m total; (5) Plan storage carefully - open-plan means you see everything; (6) Ventilation is critical - a high-extraction cooker hood (minimum 600m3/h) or ceiling-mounted extractor prevents cooking smells reaching the living area; (7) Consider an acoustic ceiling treatment if the space is large and hard-surfaced.

Question 9

What roof options are there for a kitchen extension?

Accepted Answer

Options include: (1) Flat roof with roof lantern - the most popular choice, GRP or single-ply membrane roof with a glazed lantern bringing light to the centre (total £8,000-£15,000 for the roof and lantern); (2) Flat roof with skylights - Velux or similar flat-roof windows (£800-£1,500 each installed); (3) Pitched/lean-to roof - traditional look, tiles to match existing house (£5,000-£10,000); (4) Part-glazed flat roof - larger glazed sections for maximum light; (5) Green roof - sedum or wildflower covering on a flat roof (£60-£100/m2 additional). All flat roofs must have a minimum 1:40 fall for drainage and meet Part L insulation requirements (U-value 0.18 W/m2K).

Question 10

How do I light a kitchen extension effectively?

Accepted Answer

A layered lighting plan works best: (1) Task lighting - under-cabinet LED strips for worktops (essential for food prep safety), pendant lights over the island; (2) Ambient lighting - recessed downlights on a dimmer circuit (one per 1.5-2m2 of floor area), cove lighting in ceiling details; (3) Natural light - roof lanterns, skylights and full-height glazing to the rear; (4) Accent lighting - shelf lighting, display lighting, plinth lights under kitchen units. All circuits should be on separate dimmers so you can switch between bright working mode and relaxed dining mode. Smart lighting (Philips Hue, Lutron) adds convenience but is a client-supplied second-fix item.

Kitchen Extension FAQs

Ready to start your project?