A kitchen extension is one of the most rewarding home improvements you can undertake. By extending your property to create an open-plan kitchen, dining, and living space, you can completely transform your daily lifestyle and add massive appeal for future buyers.
However, kitchen extensions are more expensive to construct than standard bedroom extensions. They require extensive plumbing, high-power electrical configurations, gas connections, ventilation, structural steel (to support knock-throughs), and high-end cabinetry. In this 2026 guide, we outline average costs, planning tips, and key considerations for your kitchen extension.
Average kitchen extension costs in 2026
On average, building a kitchen extension in the UK costs between £1,900 and £3,300 per square metre for the structural shell. A typical small kitchen extension of 20 square metres costs between £35,000 and £70,000 for construction alone, before you buy the kitchen cabinets, worktops, and appliances.
Estimated project costs by extension size and specification level (excluding VAT):
| Extension Size | Estimated Area | Average Build Cost (Shell only) |
|---|---|---|
| Small (Side Return) | 12 m² | £24,000 - £40,000 |
| Medium (Rear Extension) | 20 m² | £38,000 - £66,000 |
| Large (Open-Plan Diner) | 40 m² | £76,000 - £130,000+ |
Fitting out your new kitchen extension
When budgeting, it is critical to separate the build cost (the bricks, mortar, steel, and plastering) from the fit-out cost (the kitchen units, plumbing hookups, and finishes):
- Budget Fitting (£5,000 - £12,000): Standard MDF cabinetry from high-street suppliers, laminate worktops, and basic appliances.
- Mid-Range Fitting (£12,000 - £25,000): Solid wood or high-grade painted units, stone/quartz worktops, integrated mid-range appliances, and under-cupboard lighting.
- Premium/Bespoke Fitting (£25,000 - £50,000+): Completely custom-built cabinetry, luxury marble or Dekton worktops, high-end smart appliances, and custom kitchen islands.
Why kitchen extensions cost more than normal rooms
Several factors push kitchen extensions to the higher end of extension pricing:
- Structural Knock-Throughs: Creating a seamless open-plan space usually requires knocking down the existing rear house wall. This requires structural engineers to specify heavy steel RSJ beams, which typically costs £1,500 to £4,000 to supply and install.
- Plumbing and Drainage: Relocating sinks, washing machines, and dishwashers requires extending waste and hot/cold feed pipework under the floor, costing £1,000 to £2,500 depending on the distance to the main soil stack.
- Heating Options: Kitchen diners are large spaces with exterior glazing. Underfloor heating (UFH) is highly recommended. Expect to pay £1,500 to £3,500 for a wet underfloor heating system connected to your boiler.
- Glazing & Bi-folds: Large bi-fold doors or sliding glass panels are staple features of modern extensions. Expect to pay £3,000 to £8,000 depending on size and frame material (aluminium is premium and highly durable).
Finding trusted kitchen extension builders on GetBuilder
A kitchen extension requires coordination between builders, plumbers, electricians, and kitchen fitters. To find a vetted main contractor to manage your build, follow these steps:
- Post your requirements: State your extension dimensions and project goals for free on GetBuilder.
- Compare itemized quotes: Ensure quotes distinguish between structural shell work, utility routing (plumbing/electrics), plastering, and final kitchen installation.
- Vetted local pros: Connect with local builders holding validated references, previous project portfolios, and active insurance coverage.
