How Much Does a Single-Storey Extension Cost in the UK?
A single-storey extension is one of the most popular ways to add living space to a UK home. Costs vary enormously depending on size, specification, and location — but as a rule of thumb, expect to pay £1,500–£2,500 per square metre in most of England, or up to £3,000 per square metre in London.
Typical Cost (UK, 2026)
Approximately £1,500–£3,000 per m² including labour and materials
All costs are indicative estimates. Obtain at least 3 quotes from qualified builders. Prices exclude VAT (20%).
Factors Affecting the Cost
Size
A 20m² extension costs significantly less per square metre than a 10m² one due to fixed setup costs.
Specification
A basic extension with standard finishes will cost less than one with underfloor heating, bifold doors, and high-end kitchen.
Location
London and the South East attract a 20–30% premium over the Midlands and North.
Foundations
Ground conditions affect foundation costs significantly. Clay soils may need deeper or reinforced foundations.
Roof type
A flat roof is cheaper to build than a pitched roof. A lantern or roof light adds cost.
Structural changes
Removing a load-bearing wall adds structural engineer and steel beam costs (£2,000–£5,000 extra).
Cost Breakdown
| Item | Basic | Mid-range | High-end |
|---|---|---|---|
| Groundworks and foundations | £3,000 | £5,000 | £10,000 |
| Structure (walls, roof) | £8,000 | £15,000 | £25,000 |
| Roofing | £2,000 | £4,000 | £8,000 |
| Windows and doors | £2,000 | £5,000 | £15,000 |
| Electrics | £1,500 | £2,500 | £4,000 |
| Plumbing | £500 | £2,000 | £5,000 |
| Plastering and insulation | £1,500 | £3,000 | £5,000 |
| Flooring | £1,000 | £3,000 | £8,000 |
| Decoration | £1,000 | £2,000 | £4,000 |
| Architect and planning fees | £1,500 | £3,500 | £6,000 |
Costs are indicative and exclude VAT. Regional variations apply.
Typical Timeline
3–5 months from planning to completion
Frequently Asked Questions
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