How much does a house extension cost? How long does it take to build?
House extension prices typically start from around £1,100 per square metre (plus VAT) and rise well over £2,600 per square metre, depending on quality, complexity, specification, size, site conditions and location.
House extension cost guide
As a rule of thumb, extension prices can start from £1,100 per square metre (plus VAT) and rise well over £2,600 per square metre (plus VAT).
The final figure depends on quality, complexity, specification, shape, size, number of storeys, drainage, layout, site conditions and location. Narrow, small extensions tend to cost more per square metre than square, large ones, and prices in London are higher than in other areas.
You should also factor in kitchen elements and whether you will be able to stay in the property while the work is carried out.
Additional costs to consider
On top of the building costs, there are several other expenses to budget for:
- Drawings and structural calculations for planning and building regulations (from around £800)
- Party wall agreement (around £1,000 if an agreed surveyor is used)
- Insurance cost
- Internal alterations, rewiring, asbestos removal, a new boiler system and decoration
Example 1: single-storey extension
An 18 square metre (6m x 3m) single-storey rear extension with bi-fold doors, a roof lantern and a flat roof would cost around £27,000 plus VAT (20%), plus kitchen cabinets and sanitaryware.
This typically takes around 2 months to build, depending on site and weather conditions.
Example 2: double-storey extension
A 36 square metre (6m x 3m) double-storey rear extension would cost around £50,000 plus VAT (20%), plus kitchen cabinets and sanitaryware.
This typically takes around 3 months to build, depending on site and weather conditions.
Get multiple quotes
Because so many factors affect the final price and timeline, it is important to get multiple quotes for house extensions before you commit. These figures are general market guidance from 2020, not AVA's fee , and should be treated as a starting point.