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 Lewisham
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 Lewisham are listed below, taken from our Lewisham area page. Each one is a reason to confirm the address on Lewisham's constraints map before relying on permitted development.
- Conservation areas. Lewisham has numerous conservation areas, including large ones at Brockley and Blackheath and others in Forest Hill, Sydenham, Lee Manor, Telegraph Hill and Deptford. 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. The Brockley conservation area and some others in Lewisham carry Article 4 directions removing permitted development for front alterations, windows, roofs and boundary treatments. Coverage varies by area, so we check the schedule for your street before recommending a permitted development route.
- Ravensbourne, Quaggy and Pool river flood zones. The Ravensbourne, Quaggy and Pool rivers run through Catford, Lewisham town centre, Ladywell, Lee and Bellingham, and land along them falls within Flood Zones 2 and 3. The Thames frontage at Deptford is also Flood Zone 3. Basements and new ground-floor habitable rooms there may need a flood risk assessment. Source
- Listed buildings in Blackheath and Deptford. Blackheath, Blackheath Park, Deptford High Street and St Paul's Deptford contain many listed Georgian and Victorian buildings. Listed houses need listed building consent for almost any alteration, and extensions to neighbours are judged on their effect on the setting.
- Metropolitan Open Land. Blackheath, Hilly Fields, Beckenham Place Park, Mountsfield Park and the Waterlink Way corridor are Metropolitan Open Land. Houses fronting or backing onto them are judged on the effect of extensions and outbuildings on openness and setting.
What Lewisham planning officers look for
Lewisham's officers apply the Alterations and Extensions SPD fairly closely. Rear extensions deeper than neighbouring precedent, side returns that breach the 45-degree rule and roof extensions in Brockley, Blackheath and other conservation areas are the common refusal reasons; front dormers are resisted almost everywhere. On 1930s streets in Grove Park and Downham side extensions are expected to be set back and subordinate. Lewisham 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.
