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

A home extension in Brent typically costs £3,200 to £4,500 per m² to build in 2026, at mid-range specification, before VAT and professional fees. Planning depends heavily on the street. Brent has 22 conservation areas, from Queen's Park to Kensal Rise, and every one of them carries an Article 4 Direction removing permitted development rights for common external works. Outside them, most of the borough is ordinary permitted-development territory. This page covers what the council allows, what its January 2025 extensions guidance asks for, 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 Brent?

Many Brent 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.

Brent's conservation areas deserve particular care because all 22 have Article 4 Directions. Depending on the area, these remove permitted development rights for changing front windows and doors, painting the front of the house, paving over front gardens, removing front boundary walls, replacing roof tiles, taking down chimneys and building rear outbuildings. Queen's Park (designated 1986), Mapesbury (1982), Brondesbury (1990) and the newly designated Kensal Rise (May 2024) are among the areas affected. Separately, a borough-wide Article 4 in force since November 2022 restricts converting family homes to small HMOs; it does not affect extensions.

What does Brent's new extensions guidance mean for your project?

Brent adopted SPD2, its Residential Extensions and Alterations Supplementary Planning Document, on 16 January 2025, and it is the yardstick for every householder application in the borough. It sets out how the council judges rear and side extensions, roof alterations and outbuildings against neighbour amenity, character and daylight.

Working with the grain of that guidance is usually faster than fighting it. Brent also publishes dedicated design guides for several conservation areas, including Queen's Park, Mapesbury and Roe Green Village, which spell out expected materials and details. Checking your street against the conservation area maps and the relevant design guide is part of our Stage Zero review, before any design work starts.

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

Brent 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 Brent 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, which matters in Brent given how much of the Victorian south falls within designated areas. 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 Brent 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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