How Much Does a Single Storey Extension Cost in the UK?
A single storey rear or side extension is the most popular way to add ground-floor space. It is priced per square metre of new floor area, then adjusted for the fit-out.
Typical 15–20m² single storey extension, built and fitted. Kitchens and glazing push it higher.
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Cost by size (built & fitted)
What affects the price
- •Size and finish level — a basic shell costs far less per m² than an extension with a fitted kitchen.
- •Glazing — bifold doors, sliding doors and roof lanterns are premium items.
- •Groundworks and foundations, especially near drains, trees or on a slope.
- •Whether you are knocking through into the existing house (structural steel).
- •Planning, Building Regulations and party-wall agreements where relevant.
Regional price variation
Labour is the biggest regional swing. London and the South East typically run 20–30% above the national average, while the North of England, Scotland and Wales tend to sit 5–15% below it. Material prices are fairly consistent nationwide — it is day rates that move the total. The ranges on this page assume South of England pricing unless stated.
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Frequently asked questions
How much does a single storey extension cost in the UK?
A single storey extension typically costs £30,000–£55,000 for an average 15–20m² build, or around £1,800–£2,600 per square metre. A small 10m² extension is £18,000–£30,000 and a large one £45,000–£80,000.
Do I need planning permission for a single storey extension?
Many single storey rear extensions fall under permitted development within size limits (typically up to 3–4m deep for a terrace or semi, more for a detached house under the larger-home scheme), but you always need Building Regulations approval. Check with your local council.
How long does a single storey extension take?
A single storey extension usually takes 8–14 weeks to build, plus design and planning time beforehand. A kitchen fit-out and knock-through add to the programme.