House Extension Cost in South West England: 2026 Price Guide

Beyond the kitchen-focused rear extension, many homeowners across South West England, including in Bristol, Plymouth, Exeter and Bath, look at side-return infills or full double-storey extensions to add real square footage without moving house.

Typical costs

• Side return infill: roughly £18,000-£30,000
• Single-storey rear extension: roughly £25,000-£55,000
• Double-storey extension: £55,000-£100,000+

A double-storey extension isn't simply double the cost of a single-storey one - the roof, foundations and scaffolding are a large fixed cost, so the additional storey is often better value per square metre.

What affects the price

Properties within a conservation area face tighter controls on matching brick, roofline and window styles to the existing building, which can add to material costs even for an extension that wouldn't otherwise need planning permission. Access is another factor on tighter terraced streets, where scaffolding, skips and material deliveries often need council permits that a local builder will usually already be familiar with.

Planning permission

Side return and single-storey rear extensions often qualify for permitted development if they stay within set size limits, but double-storey extensions almost always need full planning permission - and permitted development rights have size and height limits that vary by property type, and can be reduced or removed altogether in a conservation area or on a listed building - always confirm with your local council before committing to a design.