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 Kensington and Chelsea
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 Kensington and Chelsea are listed below, taken from our Kensington and Chelsea area page. Each one is a reason to confirm the address on Kensington and Chelsea's constraints map before relying on permitted development.
- Conservation areas. More than 30 conservation areas cover roughly 70 per cent of Kensington and Chelsea, so almost every house in the borough is inside one. Roof extensions, cladding and most external alterations need planning permission rather than permitted development. The council publishes conservation area appraisals that officers use to judge design. Source
- Basement Article 4 direction and basement policy. The council has an Article 4 direction removing permitted development for basement excavations across the borough, and its Local Plan basement policy limits new basements to a single storey beneath the house and no more than half the garden, with structural, drainage, construction traffic and neighbour-impact information required. Basements are common but tightly controlled. Source
- Listed buildings. Kensington and Chelsea has thousands of listed buildings, including whole terraces and squares in Kensington, Chelsea and Notting Hill. Listed houses need listed building consent for almost any alteration, internal or external, and the setting of listed terraces is considered for extensions to neighbours.
- Article 4 directions on external alterations. Several conservation areas carry Article 4 directions removing permitted development for front alterations, painting, windows, roofs and boundary treatments. Coverage differs by area, so we check the schedule for your street before recommending any permitted development route.
- Thames flood zone. Chelsea Embankment, Cheyne Walk and the riverside streets fall within Flood Zones 2 and 3, protected by the Thames Barrier and river walls. Basements there need a flood risk assessment and may need flood-resilient design. Source
What Kensington and Chelsea planning officers look for
Kensington and Chelsea is the strictest householder planning authority in London. Officers expect extensions to be subordinate, to follow the established pattern on the terrace and to use matching materials and traditional detailing; rear extensions that rise above the closet wing, roof extensions on terraces with unbroken rooflines and any front-elevation change are commonly refused. Basements are decided as much on construction method and neighbour impact as on design. Pre-application advice is available for a fee and we recommend it for almost every project in the borough.
Fees and timelines
The council fee for a householder application is £528 and for a Lawful Development Certificate £264 (England, from 1 April 2025; verify before applying). Both are decided within 8 weeks of validation.
Our own fee for the drawings and the application is fixed once quoted and depends on the project type, its size and the constraints above. Answer six questions in the quote tool and we email you an indicative figure within minutes, then a written fixed-fee quote within 24 hours.
