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

A home extension in Bromley typically costs £2,800 to £3,800 per m² to build in 2026, at mid-range specification, before VAT and professional fees. Build costs sit at the lower end of the London range, but the planning map is busier than the leafy streets suggest: Bromley has 47 conservation areas, plus 13 designated Areas of Special Residential Character, including Petts Wood and Bickley, where the council protects the look of whole neighbourhoods. This page covers what the council allows, what those designations mean, 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 Bromley?

Many Bromley 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, and detached and semi-detached houses with generous gardens make Bromley well suited to it. Inside one of the borough's 47 conservation areas, which include Shortlands Village and Chislehurst, side extensions and rear extensions beyond 3 metres, and any rear extension of more than one storey, need planning permission.

Beyond conservation areas, Bromley's Local Plan (Policy 44) designates Areas of Special Residential Character, and the council uses Article 4 Directions to remove permitted development rights where they would harm those areas. The practical rule is the same as anywhere with layered designations: check the address before assuming anything, which is what our Stage Zero review does first.

What is an Area of Special Residential Character?

An Area of Special Residential Character is Bromley's own planning designation for residential neighbourhoods with special and distinctive qualities, protected under Policy 44 of the Bromley Local Plan. Thirteen are designated, including Petts Wood, Bickley, Chelsfield Park, Park Langley in Shortlands and the Marlings Park Estate in Chislehurst. Development within them is expected to respect and strengthen the established character: plot sizes, spacing between houses, tree cover and materials all carry weight.

Petts Wood is the best known example, an interwar garden suburb where the council applies this protection alongside Article 4 Directions. An extension there is entirely achievable, but it needs to be designed to the character of the estate rather than to the maximum the general rules allow.

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

Bromley sits in London's outer, lower-cost construction 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 Bromley costs £2,800 to £3,800 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 Bromley 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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