How much does a house extension cost in 2026?

Short answer

A single-storey extension typically costs £1,950–£2,900 per m² of floor area including VAT, and a double-storey extension £1,650–£2,500 per m² of floor area (both floors). A 20 square metre rear extension usually lands between about £40,000 and £60,000 before kitchen and finishes, with London around 30% higher.

What does the price per square metre include?

Our guide rates cover the build: foundations, walls, roof, insulation, glazing allowance, steel beams to open up the house, first and second fix electrics and heating, plastering and building control inspections. They do not include a new kitchen, flooring or decoration unless stated. Design, structural calculations and council fees are priced separately; drawings for a typical extension are £1,500–£4,500 for planning and building regulations drawings for a typical extension.

Typical guide prices by project

Project	UK guide (inc VAT)
Single-storey extension	£1,950–£2,900 per m² of floor area
Double-storey extension	£1,650–£2,500 per m² of floor area (both floors)
Side return extension	£2,300–£3,300 per m² of floor area
Wraparound extension	£2,200–£3,200 per m² of floor area
Orangery	£2,400–£3,400 per m² of floor area
Kitchen extension	£2,250–£3,400 per m² including a mid-range kitchen

What makes an extension cost more?

Ground conditions. Clay soils, trees and nearby drains can mean deeper or piled foundations.
Glazing. Large sliding or bifold doors and roof lanterns add cost quickly.
Opening up the house. Long steel beams and propping cost more than a simple doorway.
Access. Mid-terrace houses with no rear access mean materials come through the house.
Finishes. A kitchen, flooring and underfloor heating can add a third to the build cost.

How do prices vary across the UK?

Labour and materials cost most in London and the South East and least in Northern Ireland and the North East. As a rough guide, London prices run about 30% above the UK average and Northern Ireland about 14% below. Each of our local pages shows the guide range adjusted for that region.

How to get an accurate price

A guide price is a starting point. A fixed quote needs a survey and drawings so every item can be measured. Use our guide price tool for an instant range, then book a free home visit for a written, itemised quote.

Sources and further reading

Planning Portal: extensions

This guide is general information, not legal or tax advice. Rules change and depend on your property; we confirm what applies to your project at the survey.