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 Southwark
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 Southwark are listed below, taken from our Southwark area page. Each one is a reason to confirm the address on Southwark's constraints map before relying on permitted development.
- Conservation areas. Southwark has numerous conservation areas, concentrated in Camberwell, Dulwich, Peckham Rye, Nunhead, Bermondsey Street and Borough. Roof extensions and cladding in these areas need planning permission rather than permitted development. Check the council's constraints map for your address before assuming PD applies. Source
- Article 4 directions. Southwark has Article 4 directions in several conservation areas removing permitted development for front alterations and boundary treatments, and a Class MA Article 4 covering the Central Activities Zone and town centres that removes the commercial-to-residential prior approval route. We confirm coverage for your address with the council.
- Thames flood zones. Bermondsey, Rotherhithe, Borough and the riverside fall within Flood Zones 2 and 3, protected by the Thames Barrier and river walls. Basements and new ground-floor habitable rooms there may need a flood risk assessment. Source
- Listed buildings and Metropolitan Open Land. Camberwell, Dulwich Village, Borough and Bermondsey Street contain many listed buildings needing listed building consent for alterations. Dulwich Park, Peckham Rye, Burgess Park and Southwark Park are Metropolitan Open Land, and houses adjoining them are judged on openness and setting.
What Southwark planning officers look for
Southwark's officers apply the Southwark Plan and the residential design standards fairly predictably. Rear extensions deeper than neighbouring precedent, side returns that breach the 45-degree rule and roof extensions in conservation areas are the common refusal reasons; front dormers are resisted almost everywhere. On the Dulwich Estate the Estate's own design expectations are often stricter than the council's. Southwark is a busy authority and householder decisions can run past the statutory period. Pre-application advice is available for a fee.
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.
