A rear kitchen extension is the most popular home improvement project in London. It transforms the most-used room in the house — opening up the ground floor, connecting kitchen and garden, and creating the open-plan family space that modern family living demands. But what does it actually cost? Here is a realistic breakdown for 2025.
What's Included in a Kitchen Extension?
A complete kitchen extension project includes:
- Structural works (foundations, walls, roof, beam to open up the existing rear wall)
- External envelope (rear and side walls, flat roof or pitched roof, glazing)
- M&E first fix (plumbing, electrics run through new works)
- Insulation and plastering
- M&E second fix (sockets, switches, lighting, plumbing connections)
- Floor finish
- Underfloor heating if required
- Kitchen fit-out (if included in the package)
- Decoration
- Party wall works if required
- Planning (if required)
- Structural engineer fees
- Architect / design fees
Typical Costs by Extension Size
Small Extension (up to 3m × 3m, 9m²)
- Build cost (shell and plaster, no kitchen fit-out): £45,000–£70,000
- Kitchen supply and fit (mid-range): £10,000–£20,000
- Floor finish: £1,500–£4,000
- Underfloor heating: £2,500–£4,000
- Professional fees (architect, SE): £5,000–£10,000
- Approximate all-in: £64,000–£108,000
Mid-Size Extension (4m × 4m, 16m²)
- Build cost (shell and plaster): £75,000–£110,000
- Kitchen supply and fit (mid-range): £15,000–£30,000
- Floor finish: £2,500–£5,500
- Underfloor heating: £3,500–£5,500
- Professional fees: £6,000–£14,000
- Approximate all-in: £102,000–£165,000
Larger Extension (5m × 5m, 25m²)
- Build cost (shell and plaster): £110,000–£160,000
- Kitchen supply and fit (mid-range): £20,000–£40,000
- Floor finish: £3,500–£7,500
- Underfloor heating: £5,000–£8,000
- Professional fees: £8,000–£18,000
- Approximate all-in: £146,500–£233,500
What Affects Cost Most?
- Specification of glazing: Premium roof lanterns, sliding doors, and skylights versus standard units can add £10,000–£25,000
- Kitchen specification: A German engineered kitchen can cost 3–4× the price of a mid-market equivalent
- Structural complexity: Removing chimney breasts, multiple beams, or party wall complications add cost
- Finishes specification: Stone floors and premium tiling versus LVT and standard tiles
rcbGroup
rcbGroup provides detailed estimates for kitchen extension projects based on a properly specified scope — not a vague ballpark. We help clients understand what they are getting for their budget before committing to construction.