House Extension Cost in Bromley: 2026 Price Guide

Plenty of homeowners in Bromley skip the kitchen-only extension and go straight for a side-return infill or a double-storey addition, adding genuine square footage rather than moving house - a particularly obvious choice on terraces where the side return would otherwise sit unused.

Typical costs

• Side return infill: roughly £25,000-£40,000
• Single-storey rear extension: roughly £35,000-£70,000
• Double-storey extension: roughly £70,000-£130,000+

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 locally

Bromley sits within the London Borough of Bromley, and a meaningful share of its housing stock falls inside the Chislehurst and Warren Wood Estate conservation areas - 47 in total across the borough, among the most of any London borough - which affects both what you're allowed to build and what materials you're expected to use. Matching original brick, slate or stone detailing on an extension in a conservation area typically costs more than a standard modern finish, and can extend the planning timeline too.

Tighter terraced streets bring the same access problem here as with any extension: scaffolding, skips and deliveries near Beckenham Place Park often need a council permit, and a builder who already works locally will usually have been through that process before.

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 from the London Borough of Bromley. Get a pre-application check if your street falls within a conservation area - it's a small upfront cost that can save a redesign later.