The permitted development rules for loft conversions
A loft conversion with a rear dormer is permitted development on a house if the added roof volume is no more than 40 m³ on a terraced house or 50 m³ on a semi-detached or detached house, the dormer sits at least 200 mm back from the eaves and no higher than the ridge, there is no dormer on the roof slope facing the road, materials are similar in appearance, and side windows are obscure-glazed.
Flats and maisonettes have no permitted development rights, so a loft to a top-floor flat always needs planning permission. Full-width box dormers that reach the ridge, and hip-to-gable conversions on semis whose volume exceeds 50 m³, also fall outside the allowance.
What changes in Southwark
Roof extensions are not permitted development in a conservation area, so a dormer or hip-to-gable there needs a householder planning application designed to the area's appraisal.
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.
