Extensions in East Barnet: design, planning and build

Approvals for an extension in East Barnet

In England a single-storey rear extension can usually go up to 3 m beyond the original rear wall of a semi-detached or terraced house, or 4 m on a detached house, without a planning application, provided it is no more than 4 m high, keeps eaves to 3 m within 2 m of a boundary and, with other buildings, covers no more than half the land around the original house. The larger home extension prior approval scheme raises those depths to 6 m and 8 m, with neighbours notified and a 42-day decision.

In England a two-storey rear extension is permitted development only if it projects no more than 3 m from the original rear wall, sits at least 7 m from the rear boundary, matches the roof pitch and uses obscure, non-opening side windows upstairs. Most two-storey extensions therefore go through a householder planning application, which costs £548 from 1 April 2026 and normally takes about 8 weeks.

In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.

If the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations.

Applications are decided by the local planning authority (your district, borough or unitary council).

What extensions cost in East Barnet

Use these East Barnet guide prices to sense-check a budget; the guide-price tool narrows them to your own size, and the site visit turns them into a written figure.

Which extension suits a East Barnet home?

Across London, terraced houses with narrow side returns and tight access are the norm, which shapes everything from party wall notices to how materials reach the back garden.

For many houses here, side return extensions, wraparound extensions or glass box extensions gives the most useful space for the budget.

Where we work near East Barnet

We cover East Barnet and the postcode districts EN4, EN5, N14, N20. The same team covers Barnet (2 miles), Friern Barnet (2 miles), Palmers Green (3 miles), Enfield (3 miles), Finchley (3 miles), all within easy reach. Potters Bar, in Hertfordshire, is roughly 3 miles from East Barnet and also on our list.

• Barnet
• Friern Barnet
• Palmers Green
• Enfield
• Finchley