Why kitchen extensions justify their own category in London
Kitchen extensions are not 'just extensions with a kitchen in'. They are the highest-spec, highest-impact, highest-value form of home extension in London — and they bring distinct technical, design and budgeting considerations. A kitchen extension typically involves: removing the existing rear or side wall (structural), removing or modifying a second internal wall to open into adjacent dining or living space (structural), running new gas and water supplies to the new layout (if required), upgrading the consumer unit to handle induction, double-oven, dishwasher and HVAC loads (often required), specifying and installing bespoke or premium joinery cabinetry (£15,000–£60,000 separate budget), and integrating the new space with a feature glazing element (bifold/slider plus rooflight). All this within a finish quality that will sit on the cover of an architectural magazine if you choose. We build kitchen extensions weekly — it is our single most-requested service — and we have refined the process to a fine art.
Side return versus rear: the two routes to an open-plan London kitchen
On a Victorian or Edwardian terrace with a back addition (the long narrow projection at the rear), the side return alley is dead space. Infilling it adds 8–14m² of floor area, doesn't extend the rear building line (so usually permitted development with no neighbour objections), and squares off the kitchen into a usable rectangle. This is the lowest-cost, highest-value London kitchen extension move — and it's been our most-built type for the past decade. A pure rear extension, by contrast, projects beyond the existing rear wall, adds 12–25m² depending on depth, gives you a wider feature glazing run, but extends the building line into the garden (reducing outdoor space). The two are often combined as a wraparound, but cost rises sharply: a 4m rear plus 3m side return might cost £130,000–£170,000 versus £75,000 for a 6m rear alone. We assess plot, planning, light, garden use and budget — there is no universal best answer.
The structural reality: opening up the back of a London terrace
A typical London kitchen extension removes two walls: the original rear wall (carrying the floor above and the upper rear wall) and a 'spine wall' between the original kitchen and dining room. Each removal needs a steel beam, calculated by a structural engineer, sized to span the opening plus a safety factor, sitting on engineered pad-stones at each end, with the load path traced down to the foundations to confirm they can take the additional point load. For a typical 4m rear extension with a 3.5m kitchen-dining wall removal, we'd specify two beams of 254×146 UB or 254×102 UB section depending on loading. These are not casual day-rate calculations — get the spec wrong and you get cracks within months. Our in-house structural engineer signs and submits to building control, with full Sap and load calculations on file. Steels are usually exposed or boxed in plasterboard depending on aesthetic preference; exposed-and-painted is a popular industrial-loft look.
Glazing and rooflights: getting light into a north-facing London kitchen
Most London terraces face their rear elevation north or east — so a rear kitchen extension is daylight-challenged unless we engineer it. The solution is layered: full-width feature glazing (bifolds, sliders or steel-framed Crittall) at the rear delivers borrowed light from the garden; large rooflights or a roof lantern in the flat roof brings sky-light from above; clerestory windows above eye-level wall units add diffuse light without sacrificing wall space. On a typical 4×6m rear kitchen we'd specify 3.6m of bifolds or sliders, plus a 1.8×1.2m lantern, plus two 1.2×0.8m rooflights over the kitchen run. The combined effect is dramatic — average daylight factor (DF) above 4% on a 6×4m kitchen at noon, versus 1.5% in the unextended original. We model daylight in software during design before committing to specification.
Bespoke kitchen install: working with your kitchen designer or supplying through us
Roughly half our kitchen extension clients buy the kitchen separately from a specialist designer (deVOL, Naked Kitchens, Pluck, Plain English, Howdens at the budget end) and we install. The other half ask us to design and supply the kitchen end-to-end — we have an in-house joinery workshop in Bermondsey that produces hand-built cabinetry to spec, typically £18,000–£45,000 for a 25–35-unit kitchen excluding appliances and worktops. Whichever route, we co-ordinate first fix electrics and plumbing precisely to the kitchen plan: appliance points, dishwasher waste, tap and waste runs to the sink, induction-rated 32A circuits, extractor outlet, wine fridge cooling. Worktops follow second fix: stone (granite, quartz, Dekton, marble) is templated after units are in, fabricated off-site in 5–7 days, installed in a half-day. We coordinate appliance delivery (you supply the appliances, we install) within 48 hours of worktop install.
Underfloor heating, flooring and the floor build-up that ties it all together
Modern London kitchen extensions almost always specify underfloor heating (UFH) instead of radiators — wall space is at a premium and underfloor delivers a more even temperature, lower running cost, and a cleaner look. Wet UFH (warm water from the boiler) is the default for new extensions on a screed floor — heating loop laid in 100mm screed over 100mm insulation over a damp-proof membrane over the new slab. Total floor build-up: 250mm of work above the new slab, which has to be co-ordinated with door thresholds, step-ups to the existing house floor (which is usually at a different level), and the soffit height of any rear bifolds. Flooring of choice: large-format porcelain tiles (60×120 or 80×160) for a contemporary look; engineered oak boards (180–220mm wide) for a softer, warmer feel; or polished concrete for an industrial palette. Each has different installation requirements that we manage end-to-end.
Cost breakdown on a £110k kitchen extension: where the money sits
On a £110,000 rear kitchen extension: £14,000 groundworks and foundations, £17,000 superstructure (walls, roof, steels), £14,000 glazing (bifold + lantern + 2 rooflights), £9,000 electrics first and second fix (full new circuits, dimmable LED scheme, USB outlets, smart switches), £7,500 plumbing and heating (UFH, new gas line, rad zones), £6,500 plastering and decoration, £8,000 flooring (porcelain large-format with UFH installation), £7,500 worktops (quartz, 60mm), kitchen units excluded as separate, £4,000 lighting and joinery trim, £4,500 external (patio, threshold, drainage), £10,000 fees, £6,500 site management, £6,000 margin and contingency. Kitchen units, appliances and tap/sink are budgeted separately by you, typically £20,000–£45,000. The total walk-in cost — extension plus kitchen plus appliances — usually lands £140,000–£170,000 for a high-spec London terraced kitchen extension.
