Single or two-storey extension: which is right for you?

Cost

National guides for 2026 put build costs, before VAT, at roughly:

• Single-storey: about £2,200 to £3,300 per m²
• Two-storey: about £2,000 to £3,200 per m²

A two-storey extension costs more in total, but often less per square metre, because the foundations and roof cover two floors. See extension costs in North Devon.

Planning

• Single-storey rear extensions up to 3 m (semi or terrace) or 4 m (detached) can often be permitted development, and up to 6 m or 8 m through the larger home extension scheme.
• Two-storey rear extensions can be permitted development only if they are no more than 3 m deep and at least 7 m from the rear boundary, with other conditions. Many need planning permission.
• In conservation areas and the North Devon Coast National Landscape, two-storey extensions always need planning permission.

Space and garden

A single-storey extension uses more garden for the same floor area. A two-storey extension adds bedrooms or a bathroom upstairs as well as living space, while keeping more of the garden.

Disruption

Single-storey extensions are usually quicker, and most of the work happens outside until the final break-through. Two-storey extensions involve more work on the existing house, especially where the new upstairs joins the old.

Which is right?

• Choose single-storey for a bigger kitchen or open-plan living space, a quicker build, or where planning or neighbours rule out going up.
• Choose two-storey when you need extra bedrooms, want the most space for the money, or have a small garden.

Talk it through

We can look at your house, check what planning allows, and price both options. See extensions, or our Barnstaple and Bideford pages.