How much does a house extension cost in London?
A 2026 guide to single and double-storey extension costs in London.
Extensions in London cost more per square metre than most of the UK, with central boroughs highest. Here is what to expect in the capital in 2026.
Typical London extension costs
| Type | Typical London cost (2026) |
|---|---|
| Single-storey (outer London) | £2,500–£3,500 / m² |
| Single-storey (inner London) | £3,500–£5,000 / m² |
| Typical 20 m² extension | £50,000–£120,000 |
| Double-storey | Lower per m², higher total |
| Design, planning & VAT | Extra |
These are typical London guide prices for 2026 and will vary by job, borough and property. Always get written quotes for your own project.
What affects the cost?
- The size and specification
- Groundworks and structural work
- Inner versus outer London borough
- Access and materials storage on tight sites
- Design, structural engineer and building-control fees
- VAT
Extension costs across London
In London, single-storey extensions commonly run £2,500–£5,000 per square metre, with central boroughs 20–40% higher than outer London. Quotes are usually for construction only — add VAT and professional fees.
How to get a fair price in London
Get detailed like-for-like quotes, use a written contract with staged payments, and confirm who handles planning, party-wall and building control. See our full UK house extension cost guide.
Frequently asked questions
How much is a single-storey extension in London?
Around £2,500–£5,000 per square metre for construction, so a typical 20 m² extension often costs £50,000–£120,000 depending on the borough and finish — before VAT and fees.
Why are London extensions so expensive?
Higher labour rates, tight sites with difficult access, and premium finishes push London extension costs above the national average, with central boroughs highest.
Do quotes include VAT and fees?
Usually not. Extension quotes are typically for construction only — budget separately for VAT, design, structural engineer and building-control costs.
Planning an extension in London?
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