House Extension Cost in Greenwich: 2026 Price Guide

Beyond the kitchen-focused rear extension, many homeowners in Greenwich look at side-return infills or full double-storey extensions to add real square footage without moving house - particularly on the terraced streets where a side return is otherwise wasted space.

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

A significant part of Greenwich falls inside the Greenwich Town Centre and Maritime Greenwich conservation areas, part of a UNESCO World Heritage Site, part of the Royal Borough of Greenwich's wider planning area - which shapes both what's permitted and what materials are expected. Matching original brick, slate or stone detailing here usually costs more than a standard modern finish, and tends to add time to the planning process as well.

Tighter terraced streets bring the same access problem here as with any extension: scaffolding, skips and deliveries near the Cutty Sark, the Royal Observatory and the Old Royal Naval College 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 Royal Borough of Greenwich. 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.