Rear extensions in Barnet depend on the house. Typical homes here: 1930s semi-detached houses in Finchley, Hendon, Edgware, Mill Hill and Whetstone; Arts and Crafts and neo-Georgian houses in Hampstead Garden Suburb. Designations to check first: Hampstead Garden Suburb: Article 4 direction and Trust consent; Conservation areas; Green Belt. Applications are decided by London Borough of Barnet and the Barnet Local Plan.
The permitted development rules for rear extensions
On a house, a single-storey rear extension is permitted development if it projects no more than 3 m from the original rear wall on a terraced or semi-detached house, or 4 m on a detached house, is no higher than 4 m, has eaves no higher than 3 m where it comes within 2 m of a boundary, and uses materials similar in appearance to the house. The larger home extension route allows 6 m or 8 m through a 42-day prior approval, where the council consults the neighbours.
Flats and maisonettes have no householder permitted development rights, so any rear extension to a flat needs planning permission. Previous extensions count against the allowance, and the larger home extension route is not available in conservation areas.
What changes in Barnet
In a conservation area a single-storey rear extension can still be permitted development within the 3 m or 4 m limit, but cladding it in materials that differ from the house is not, and the 6 m and 8 m prior approval route is closed.
The local constraints that most often decide the route in Barnet are listed below, taken from our Barnet area page. Each one is a reason to confirm the address on Barnet's constraints map before relying on permitted development.
- Hampstead Garden Suburb: Article 4 direction and Trust consent. Hampstead Garden Suburb is a conservation area with a long-standing Article 4 direction that removes most householder permitted development rights, so almost any external change needs planning permission. Source
- Conservation areas. Barnet has numerous conservation areas, including Hampstead Garden Suburb, Monken Hadley, Totteridge, Mill Hill, Finchley Church End and Hendon (The Burroughs). Source
- Green Belt. Large tracts of Totteridge, Arkley, Mill Hill and the northern fringe of the borough are Green Belt. Source
- Other Article 4 directions and HMOs. Beyond Hampstead Garden Suburb, Barnet may have Article 4 directions affecting other conservation areas and houses in multiple occupation. Source
What Barnet planning officers look for
The most common refusal reasons we encounter are two-storey side extensions that are not set back from the front elevation and create a terracing effect between semis, rear extensions deeper than the neighbour's that fail the 45-degree test, and front dormers. Hip-to-gable lofts are normally acceptable outside conservation areas. Barnet offers a paid pre-application service, worth using in Hampstead Garden Suburb and the Green Belt. Decision times often exceed the statutory 8 weeks; a written extension of time is common.
Fees and timelines
Barnet decides a householder application or a Lawful Development Certificate within 8 weeks of validation. The council fee is £528 for a householder application and £264 for a Lawful Development Certificate (England, from 1 April 2025; verify before applying).
Our own fee is fixed once quoted. The quote tool gives an indicative figure in minutes and a written quote follows within 24 hours.
Primary sources
- The Town and Country Planning (General Permitted Development) (England) Order 2015, Schedule 2: the permitted development limits quoted above.
- Planning Portal: do you need permission: the national guidance and the application service every council accepts.
- London Borough of Barnet: planning: the council's own constraints map, validation checklist and pre-application service.
