# House extensions in Barnet

Canonical URL: https://mirion.uk/areas/barnet/extensions/

> Rear, side, wraparound and two-storey extensions in Barnet under the council's June 2026 guidance: depths, heights, garden limits and boundary gaps.

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.

### 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.

Barnet extensions: common questions

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.