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

A home extension in Southwark typically costs £4,000 to £5,500 or more per m² to build in 2026, at mid-range specification, before VAT and professional fees. The planning picture varies sharply across the borough: 48 conservation areas, an Article 4 Direction over the Sunray Estate in north Dulwich, and a second layer of control in Dulwich itself, where the Dulwich Estate's Scheme of Management requires its own approval on top of planning permission. This page covers what applies where, and what building actually 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 Southwark?

Plenty of Southwark extensions still proceed without a planning application. 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 the borough's 48 conservation areas, side extensions and rear extensions beyond 3 metres, along with any multi-storey rear extension, need planning permission.

One conservation area carries a specific householder Article 4 Direction: the Sunray Estate on Denmark Hill in north Dulwich, covering Sunray Avenue, Sunray Gardens, Casino Avenue, Nairne Grove, Red Post Hill and part of Herne Hill, where development that would normally be permitted requires an application. The council's other Article 4 Directions mainly concern HMOs, demolition, pubs and commercial changes of use rather than home extensions.

Dulwich adds a further layer. Across the Dulwich Estate, alterations and extensions need approval under the Estate's Scheme of Management as well as any council permission, a separate process that typically takes eight to ten weeks. Checking which of these layers applies to your address is part of our Stage Zero review, before any design work starts.

What kind of homes are we extending in Southwark?

Southwark runs from riverside warehouses to leafy Victorian suburbs in the space of four miles. Bermondsey and Borough hold converted warehouses and mansion flats, where extensions are rare and internal reconfiguration rules. Camberwell keeps some of south London's best Georgian terraces. East Dulwich, Nunhead and Peckham Rye are classic Victorian terrace territory, and Dulwich Village adds detached and semi-detached period houses under the Estate's watchful eye.

The staple brief in East Dulwich and Peckham is the side-return or wraparound kitchen extension with a loft conversion above. Georgian properties in Camberwell need a lighter touch and often listed building awareness. In Dulwich, designs must satisfy the Scheme of Management's design guidelines as well as the council, which rewards getting both consents moving early and in parallel.

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

Southwark sits in London's inner-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 Southwark costs £4,000 to £5,500 or more 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, and Dulwich Estate approval adds programme time more than cost. 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 by extension type and specification level is in our free Extension Cost Guide 2026, no email required. To see how we design and deliver this kind of work, with real budgets attached, have a look at the Rathcoole Gardens project page and the Drakefield House project page, two completed London projects.

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 Southwark 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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