How much does an extension cost in 2026?
Most house extensions in the UK cost between about £2,400 and £4,700 per square metre including VAT in 2026. A single-storey rear extension typically runs from £2,600 to £4,000 per square metre, two-storey extensions are cheaper per square metre, and side return and wraparound extensions cost the most because of the steelwork and glazing involved.
What does an extension cost per square metre?
These are guide ranges including VAT at 20%, for the building work from foundations to a decoration-ready finish:
| Extension type | Standard | Good | High |
|---|---|---|---|
| Single-storey | £2,600 to £3,000 | £3,000 to £3,500 | £3,500 to £4,000 |
| Two-storey | £2,400 to £2,900 | £2,900 to £3,400 | £3,400 to £3,850 |
| Side return | £3,350 to £3,700 | £3,700 to £4,150 | £4,150 to £4,550 |
| Wraparound | £3,400 to £3,800 | £3,800 to £4,250 | £4,250 to £4,700 |
Figures are per square metre of new internal floor area. London and the South East usually sit at the top of each range or above it.
What does a typical extension cost in total?
A 20 m² single-storey rear extension at a good specification usually comes to around £60,000 to £70,000 including VAT. A two-storey extension adding 40 m² across both floors is often around £115,000 to £135,000. A new kitchen, if you are replacing it at the same time, typically adds £10,000 to £40,000.
What makes an extension cost more?
- Glazing. Large sliding or bifold doors, roof lanterns and glazed roofs are among the most expensive elements.
- Structure. Removing the back wall of the house needs steel beams; corners and wide openings need more steel.
- Ground and drains. Poor ground needs deeper or engineered foundations, and a public sewer under the footprint needs a build-over agreement or diversion.
- Access. Terraces with access only through the house take longer.
- Finish. Underfloor heating, high-end flooring and bespoke joinery move a project up a tier.
What costs are on top of the build?
Budget separately for design fees (drawings, structural calculations), council fees for planning and building control, party wall surveyor fees if a neighbour appoints one, and a contingency of around 10%. Our quotes list which of these are included so you can compare like with like.
Is VAT charged on an extension?
Yes. Extensions and alterations to an existing home are standard-rated at 20% when built by a VAT-registered contractor. Reduced rates apply only in specific cases, such as renovating a home that has been empty for two years or more, or converting a building so that the number of homes changes.
Related projects
- Single-storey extensions
- Double-storey extensions
- Side return extensions
- Wraparound extensions
- Kitchen extensions
This guide is general information about building work in the UK, not legal or tax advice. Rules change, so check the current position for your property with the council, HMRC or a qualified adviser before relying on it.