How much does a house extension cost in the UK?
Last updated 9 July 2026 · 7 min read · Reviewed by the GotAPal editorial team
Heads up on prices: the figures below are broad UK guide ranges based on common market rates. Actual costs vary by region, job and tradesperson. Always confirm the price directly with the trade before booking.
An extension is one of the biggest jobs most homeowners ever take on, and prices vary hugely by size, finish and where you live. Extensions are usually costed per square metre, so once you know the going rate you can sanity-check any builder's quote.
The short version
- Single-storey extensions typically cost £1,800 to £3,000 per m², before finishes.
- In London and the South East, expect £2,800 to £4,500 per m².
- A typical 20m² rear extension runs about £40,000 to £55,000.
- Kitchens, bathrooms and high-end glazing are extra, and so is VAT.
- Get a detailed, itemised written quote and pay in stages, never a big lump up front.
The short answer
- Single-storey: £1,800 to £3,000 per m² at standard quality (before kitchens/bathrooms).
- Double-storey: often £1,500 to £2,200 per m², better value per m² as you share foundations and roof.
- London and the South East: add roughly 20 to 40%.
Typical prices
Guide figures including labour and materials, before finishes and VAT.
| Item | Typical cost |
|---|---|
| Single-storey extension (per m²) | £1,800 to £3,000 |
| Double-storey extension (per m²) | £1,500 to £2,200 |
| Typical 20m² rear extension | £40,000 to £55,000 |
| Builder day rate (labour) | £200 to £300 |
| Labourer day rate | £120 to £180 |
| Architect / drawings | £1,500 to £5,000 |
| Structural engineer | £400 to £1,000 |
What affects the price
- Size and finish. Standard vs premium fittings can swing the total by tens of thousands.
- Groundworks. Deep foundations, drains or tricky access push costs up fast.
- Glazing. Bifold doors and large rooflights are lovely but pricey.
- Location. London and the South East carry a clear premium.
- VAT. Most extensions are standard-rated, so factor 20% in.
How to get a fair deal
- Get an itemised written quote: labour, materials, and what's excluded.
- Ask the right questions before you sign. (See questions to ask before hiring a builder.)
- Pay in stages tied to progress, never a large sum up front.
- Compare two or three quotes and check reviews and insurance.
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