Kitchen Extension Cost Guide 2026
A kitchen extension is one of the most popular home improvement projects in the UK, typically adding both living space and property value. Costs vary significantly depending on size, specification, and where you live. This guide breaks down what you should expect to pay in 2026, based on real trade cost data across 14 categories.
Whether you're planning a modest galley extension or a large open-plan kitchen-diner, understanding the cost components helps you evaluate builder quotes and spot potential overcharges before committing.
Cost summary
| Size | Basic | Standard | Premium |
|---|---|---|---|
| 20m² | £17,020 | £30,400 | £47,120 |
| 30m² | £25,530 | £45,600 | £70,680 |
| 40m² | £34,040 | £60,800 | £94,240 |
Costs shown are direct trade costs (national average). Apply regional factors below for your area. Main contractor route adds 20–35%.
Trade-by-trade breakdown
Standard specification, mid estimate. Per-sqm rates for direct trades.
Regional cost variations
| Region | Factor | Adjusted cost |
|---|---|---|
| Inner London | ×1.35 | £2,052/m² |
| Outer London | ×1.22 | £1,854/m² |
| South East | ×1.08 | £1,642/m² |
| South West | ×1.00 | £1,520/m² |
| East Midlands | ×0.92 | £1,398/m² |
| North West | ×0.90 | £1,368/m² |
| North East | ×0.85 | £1,292/m² |
Multiply the national average cost by the regional factor for your area.
Key cost factors
Size and layout complexity
Larger extensions benefit from economies of scale, but L-shaped or wrap-around designs add structural complexity and cost.
Foundation type
Standard strip foundations suit most ground conditions. Poor ground may require piled foundations, adding £5,000–£15,000.
Specification level
Premium kitchens (stone worktops, integrated appliances, underfloor heating) can double the fit-out cost compared to basic spec.
Planning and Building Regs
Permitted development covers many single-storey rear extensions. Full planning adds 8–12 weeks and £200–£500 in fees.
Access and site constraints
Restricted access for deliveries, shared walls, or sloping sites increase costs by 10–20%.
Frequently asked questions
How much does a kitchen extension cost per m²?
In 2026, expect £670–£1,840 per m² depending on specification. Standard spec averages around £1,190/m² for direct trade costs, or £1,550–£1,670/m² with a main contractor.
Do I need planning permission for a kitchen extension?
Many single-storey rear extensions fall under permitted development rights. However, if your extension exceeds certain size limits, is on designated land, or faces a highway, you'll need full planning permission.
How long does a kitchen extension take to build?
A typical 20–30m² kitchen extension takes 12–16 weeks from groundworks to completion. Larger or more complex builds may take 20+ weeks.
Should I use a main contractor or manage trades myself?
A main contractor adds 20–35% markup but handles coordination, scheduling, and liability. Managing trades directly saves money but requires significant time and construction knowledge.
What adds the most value to a kitchen extension?
Open-plan layouts with good natural light, quality flooring, and a well-designed kitchen consistently add the most value. Bi-fold or sliding doors connecting to the garden are particularly valued.
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