Rear extensions for detached houses

What can you do with the back of a detached house?

Width is the opportunity. A full-width extension can hold a kitchen, dining area and family room side by side, each with its own doors to the garden. A vaulted pitched roof or a central glazed gable gives height that a flat roof cannot.

How much does a detached house rear extension cost?

Allow £1,950–£3,200 per square metre including VAT for a standard specification. A 4 m × 6 m extension typically comes to £47,000–£77,000, and a 5 m × 8 m extension to £78,000–£128,000. Oak frames and structural glazing are at the top of the range.

Do you need planning permission?

In England a single-storey rear extension can often be built under permitted development: up to 3 metres beyond the original rear wall of an attached house, or 4 metres on a detached house, no higher than 4 metres, with eaves no higher than 3 metres if any part is within 2 metres of a boundary.

England also has the larger home extension route: a single-storey rear extension of up to 6 metres on an attached house or 8 metres on a detached house, after prior approval from the council. The council notifies your neighbours and has 42 days to decide; the fee is £249 (£310 for applications made from 8 December 2026). The route is not available on designated land such as conservation areas.

What is included?

• Full-width design options
• Vaulted, flat or glazed-gable roofs
• Oak, steel or timber frames
• Large-format glazing
• Heating and ventilation for big rooms
• Landscaping tie-in with the patio
• Planning or prior approval
• Building control sign-off

Guide prices by region

Per square metre of new floor, including VAT, standard specification.