Home Extension Design in Greenwich: Planning, Costs and What's Realistic in 2026

A home extension in the Royal Borough of Greenwich typically costs £3,200 to £4,500 per m² to build in 2026, at mid-range specification, before VAT and professional fees. Much of the borough, from Charlton's terraces to Eltham's interwar semis, sits in ordinary permitted-development territory. The exceptions are its conservation areas and a set of Article 4 direction areas, including West Greenwich, the Ashburnham Triangle and the Progress Estate, where the council says you may need permission for most works, down to replacing windows and doors. This page covers what the council allows and what it costs.

Studio MASS is a residential design practice led by an architectural technologist. We design and deliver extensions, loft conversions and refurbishments across London, from first feasibility check to completed build.

Do you need planning permission for an extension in Greenwich?

Many Greenwich extensions do not need planning permission. Outside conservation areas, a single-storey rear extension up to 3 metres beyond the original rear wall (4 metres on a detached house) usually falls under permitted development. Inside a conservation area, side extensions and rear extensions beyond 3 metres, and any rear extension of more than one storey, need planning permission.

Royal Greenwich has designated conservation areas across the borough, from the World Heritage streets of West Greenwich to Victorian Westcombe Park and the garden-suburb Progress Estate in Eltham. The council's conservation pages list each area with maps, and the first feasibility step is always the same: check the address against the conservation area and Article 4 boundaries before assuming permitted development applies.

Where do Greenwich's Article 4 directions apply?

Greenwich uses Article 4 directions where it judges an area's character to be under threat, and most of them cover conservation areas. In these areas less permitted development is allowed, and the council's own guidance says you may need to apply for planning permission for most works, including replacing windows and doors and re-roofing.

Named Article 4 areas with published council guidance include the Ashburnham Triangle (a 2013 direction confirmed in May 2014, replacing a 1994 direction), West Greenwich, East Greenwich, Trenchard Street, Rectory Field, Shrewsbury Park and the Progress Estate. Each has its own guidance note setting out which works need permission, so the practical rule in these streets is to check before ordering so much as replacement windows.

How much does a home extension cost in Greenwich in 2026?

Greenwich sits in London's mid-price construction zone. From our 2026 Extension Cost Guide, built from BCIS indices, FMB build cost data and our own completed projects:

A single-storey extension in Greenwich costs £3,200 to £4,500 per m² at mid specification in 2026. A loft conversion runs £3,200 to £3,800 per m². Conservation area projects carry roughly 15% on top for material restrictions and period-appropriate detailing. These figures are construction only; VAT at 20% and professional fees are additional.

Before a brick is laid, expect £8,000 to £16,000 in professional and statutory fees on a typical project, including the £548 planning application fee that applies from April 2026.

The full breakdown is in our free Extension Cost Guide 2026, no email required. For a sense of how we work and what finished projects cost, see the Rathcoole Gardens project page and the Drakefield House project page, both completed London projects with real budgets.

Who designs your extension if not an architect?

An architectural technologist designs buildings with a focus on how they are built: construction detail, building regulations, and buildability, alongside layout and light. In the UK "architect" is a legally protected title, so we don't use it. What matters for a Greenwich extension is the same either way: design within the local planning context, technical drawings a builder can price accurately, and someone accountable from first idea to finished build. That is what we do, through one team and five stages, starting with a Stage Zero review that tells you what is realistic for your budget and what planning will allow before design begins.

Start with a conversation

The best starting point is our short questionnaire. It takes a few minutes and tells us about your home, your brief and your budget. We review it and arrange a free thirty-minute call, with an honest view on feasibility either way.

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