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

A home extension in Camden typically costs £4,000 to £5,500+ per m² to build in 2026, at mid-range specification, before VAT and professional fees. Camden sits in inner London's most expensive construction zone, and its planning environment is among the tightest in the capital: conservation areas blanket much of the borough, Article 4 Directions in areas like Hampstead and Belsize remove ordinary householder rights, and every basement excavation in the borough needs planning permission. 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 Camden?

Some Camden extensions still fall under permitted development. Outside conservation areas, a single-storey rear extension up to 3 metres beyond the original rear wall (4 metres on a detached house) usually needs no planning application, and that covers a share of the Victorian terraces in Kentish Town, Gospel Oak and Dartmouth Park. Inside a conservation area, side extensions and rear extensions beyond 3 metres, and any rear extension of more than one storey, need planning permission.

Camden then goes further than most boroughs. Article 4 Directions remove additional permitted development rights from houses and flats in several conservation areas, including Belsize, Hampstead (with a separate Direction for Frognal Way), Fitzjohns Netherhall, Primrose Hill, South Hampstead (formerly Swiss Cottage), South Hill Park Estate and Redington Frognal. A batch of updated Directions for Belsize, Hampstead, Fitzjohns Netherhall, South Hampstead and Redington Frognal was adopted on 9 June 2026, each with its own fact sheet and design guide, so the rules on your street may have changed recently. Checking the current Direction against your address is the first job, before any design work.

Why does every Camden basement need planning permission?

Camden operates a borough-wide Article 4 Direction on basements, adopted with effect from 1 June 2017. It removes permitted development rights for basement excavation across the whole borough, so every basement scheme needs a planning application and is assessed against the council's basement policies, including impacts on neighbours, drainage and ground conditions. If you are weighing a basement against a rear extension or loft conversion in Camden, factor in the extra application work, technical reports and programme time from the start.

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

Camden sits in London's inner price band. From our 2026 Extension Cost Guide, built from BCIS indices, FMB build cost data and our own completed projects:

A single-storey extension in Camden costs £4,000 to £5,500+ per m² at mid specification in 2026. A loft conversion runs £3,200 to £3,800 per m², with inner-London projects tending toward the top of that range. 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 Camden 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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