Two-storey 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 two-storey extensions
A two-storey rear extension is permitted development only within tight limits: no more than 3 m deep, at least 7 m from the rear boundary, no higher than the existing house, eaves matching the existing eaves, materials similar in appearance, and any upper-floor side window obscure-glazed and non-opening below 1.7 m.
Most two-storey extensions exceed one of those limits, most often the 7 m rear boundary rule on London plots, so the usual route is a householder planning application. Flats have no permitted development rights.
What changes in Barnet
Extensions of more than one storey are not permitted development in a conservation area, so planning permission is always needed there.
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.
