What changed in Barnet's extension guidance in 2026?

The Sustainable Design and Development Guidance SPD, adopted on 15 June 2026, replaced the 2016 Residential Design Guidance. Part 4 now sets explicit maximum depths and heights for each type of extension, with diagrams.

Can I build a wraparound extension in Barnet?

Yes. Barnet's 2026 guidance allows extensions into the side return of an outrigger and wraparound extensions, which should not normally project more than 3 metres beyond the outrigger's two-storey rear wall. The council may ask for skylights or internal openings so rooms behind still get daylight.

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Extensions · Barnet

House extensions in Barnet

We build rear, side, wraparound and two-storey extensions across Barnet, designed to the council's Sustainable Design and Development Guidance SPD adopted in June 2026.

Area: Barnet
Planning authority: London Borough of Barnet

Single-storey brick rear extension with a glazed hipped roof and dark grey sliding doors on a semi-detached house, opening onto a grey patio and lawn — AI-generated illustration; not a completed Mirion project.

What to know in Barnet

Barnet's 2026 limits for single-storey rear extensions

Width: up to the full width of the original house.
Depth: a maximum of 3 metres on terraced houses, 3.5 metres on semi-detached houses and 4 metres on detached houses, measured from the original rear wall.
Height: up to 4 metres, with eaves no higher than 3 metres.
Garden: no more than half the length of the garden, keeping the Local Plan's outdoor amenity space standards.

If the council has already confirmed a larger extension through the prior approval process, those approved dimensions can be built instead. Flat roofs on single-storey extensions should not be used as balconies.

Side, wraparound and two-storey extensions

Single-storey side extensions should be no more than half the width of the original house. Extensions to outriggers can fill the side return, and wraparound extensions should not normally extend more than 3 metres beyond the outrigger's two-storey rear wall, or be more than 2 metres high on the boundary. Two-storey side extensions keep a 1-metre gap to the boundary at first floor and are set down 0.5 metres from the ridge. Two-storey rear extensions are usually limited to 3 metres deep, kept 1 to 2 metres from the boundary depending on the neighbour, with no flat roof.

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

Barnet extensions: common questions

: The Sustainable Design and Development Guidance SPD, adopted on 15 June 2026, replaced the 2016 Residential Design Guidance. Part 4 now sets explicit maximum depths and heights for each type of extension, with diagrams.
: Yes. Barnet's 2026 guidance allows extensions into the side return of an outrigger and wraparound extensions, which should not normally project more than 3 metres beyond the outrigger's two-storey rear wall. The council may ask for skylights or internal openings so rooms behind still get daylight.