How Much Does a Rear Extension Cost in the UK?
A single-storey rear extension is the most straightforward way to extend a UK home. It extends the back of the house into the garden, typically to create a larger kitchen, kitchen-diner, or open-plan living space. Under permitted development rules, many rear extensions can be built without planning permission, though this depends on the size, property type, and location.
Typical Cost (UK, 2026)
Approximately £1,500–£2,500 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
Depth
Permitted development allows 3m (attached) or 4m (detached) without planning permission. Larger extensions require full planning permission.
Width
A full-width rear extension maximises floor area and typically reduces cost per square metre.
Roof type
A flat roof with an internal gutter is cheapest. A pitched roof, roof lantern, or fully glazed roof all add cost.
Glazing
Bifold or sliding doors across the rear elevation are popular but add £5,000–£15,000 compared with a standard French door.
Groundwork
Good ground conditions with strip foundations are cheapest. Clay or made ground may need deeper foundations.
Location
London and the South East attract a 20–30% premium. Northern England and Wales are at the lower end of the range.
Cost Breakdown
| Item | Basic | Mid-range | High-end |
|---|---|---|---|
| Foundations and groundworks | £4,000 | £7,000 | £12,000 |
| Walls (blockwork, brick outer leaf) | £5,000 | £9,000 | £15,000 |
| Roof structure and covering | £4,000 | £7,000 | £12,000 |
| Windows and bifold / sliding doors | £3,000 | £7,000 | £15,000 |
| Internal finishes (plaster, screed, flooring) | £4,000 | £8,000 | £14,000 |
| Electrics and plumbing | £3,000 | £5,500 | £9,000 |
| Architect and planning fees | £2,000 | £4,000 | £7,000 |
Costs are indicative and exclude VAT. Regional variations apply.
Typical Timeline
10–14 weeks on site
Frequently Asked Questions
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