How deep can a rear extension be in Brent?

With planning permission, Brent's 2025 SPD says single-storey rear extensions could be up to 6 metres deep on terraced and semi-detached homes and 8 metres on detached homes, as long as they use no more than half the garden. Without an application, permitted development allows 3 metres (4 metres detached), or up to 6 or 8 metres through prior approval.

Does Brent's extensions SPD apply in conservation areas?

No. The SPD says it is not intended for properties in conservation areas or for listed buildings. In those areas the relevant conservation area design guide applies, and Brent's Article 4 directions may remove permitted development rights.

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Extensions · Brent

House extensions in Brent

We design and build rear, side, side-return and wraparound extensions across Brent, working to the council's Residential Extensions and Alterations SPD adopted in January 2025.

Area: Brent
Planning authority: London Borough of Brent

Kitchen-diner in a side-return extension of a Victorian terraced house, with a glazed roof along an exposed London stock-brick wall and glazed doors to a small courtyard — AI-generated illustration; not a completed Mirion project.

What to know in Brent

What Brent's 2025 guidance allows

Single-storey rear extensions could be up to the full width of the original house and up to 6 metres deep on terraced and semi-detached homes, or 8 metres on detached homes, but no more than half the length of the garden.
Height: extensions up to 3 metres deep (4 metres on a detached house) could be up to 4 metres high with eaves no higher than 3 metres; deeper ones should keep the eaves to 2.5 metres along the boundary.
Two-storey rear extensions are limited to 3 metres deep on attached homes and 4 metres on detached homes, and must stay within a 45-degree line from the nearest habitable-room windows next door.
Side extensions should be no wider than two-thirds of the original house. A two-storey side extension should be set back at least 0.5 metres at first floor and roofed to match the house.
Outrigger extensions on Victorian houses could fill the side return and extend up to 3 metres beyond the end of the outrigger, at a maximum of 3.5 metres high.

These are guidance figures, not guarantees. The council still looks at neighbours' windows, ground levels and existing extensions, and the SPD is not used in Brent's 22 conservation areas, where the relevant design guide applies instead.

Permitted development first

Many Brent houses can add a single-storey rear extension of up to 3 metres (4 metres if detached) without an application, or up to 6 or 8 metres through prior approval, provided the house keeps its permitted development rights and is not on designated land. We check which route is quickest and safest for your house before any design work. See the Planning Portal's extension guidance for the national limits.

How we approach extensions

Our process, from survey and design to building and handover, is explained on the main service page.

Go to our main extensions page

Brent extensions: common questions

: With planning permission, Brent's 2025 SPD says single-storey rear extensions could be up to 6 metres deep on terraced and semi-detached homes and 8 metres on detached homes, as long as they use no more than half the garden. Without an application, permitted development allows 3 metres (4 metres detached), or up to 6 or 8 metres through prior approval.
: No. The SPD says it is not intended for properties in conservation areas or for listed buildings. In those areas the relevant conservation area design guide applies, and Brent's Article 4 directions may remove permitted development rights.