Rear extensions in Westminster depend on the house. Typical homes here: Stucco terraces and garden squares in Pimlico, Belgravia and Bayswater; Georgian townhouses and terraces in Marylebone, Mayfair, Fitzrovia and Soho. Designations to check first: Conservation areas; Basement Article 4 direction and basement policy; Listed buildings. Applications are decided by City of Westminster and the Westminster City Plan 2019–2040.
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 Westminster
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 Westminster are listed below, taken from our Westminster area page. Each one is a reason to confirm the address on Westminster's constraints map before relying on permitted development.
- Conservation areas. More than 50 conservation areas cover the great majority of Westminster's housing, including Pimlico, Belgravia, Bayswater, Maida Vale, St John's Wood and Queen's Park. Source
- Basement Article 4 direction and basement policy. Westminster has an Article 4 direction removing permitted development for basement excavations, and its City Plan basement policy limits new basements to a single storey beneath the house and no more than half the garden, with structural, drainage and construction management information required. Source
- Listed buildings. Westminster has more listed buildings than any other London borough, including whole terraces and squares in Belgravia, Pimlico, Mayfair and Marylebone.
- Class MA and other Article 4 directions. A Class MA Article 4 direction removes the commercial-to-residential prior approval route across the Central Activities Zone, and several conservation areas carry directions removing permitted development for front alterations.
- Thames flood zone. Pimlico, Millbank, Victoria Embankment and the riverside fall within Flood Zones 2 and 3, protected by the Thames Barrier and river walls. Source
What Westminster planning officers look for
Officers expect extensions to be subordinate, to follow the established pattern on the terrace and to use matching materials; rear extensions above closet-wing height, roof extensions on terraces with unbroken rooflines and front-elevation changes are commonly refused. Pre-application advice is available for a fee and we recommend it for most projects in the City.
Fees and timelines
Westminster 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.
- City of Westminster: planning: the council's own constraints map, validation checklist and pre-application service.
