What conservation area designation means
A conservation area is a designated zone where the local authority has determined the architectural or historic character justifies special protection. There are over 1,100 conservation areas in London covering significant portions of every borough. Designation does not stop development — it changes the planning regime. Within a conservation area: permitted development rights for cladding, painting, satellite dishes and many alterations are removed by the GPDO directly. Article 4 Directions can additionally remove PD rights for windows, doors, roof slopes and rear extensions. The council publishes a Conservation Area Appraisal and Management Plan for each area setting out the protected character — what materials, scale and detailing are expected. Most heritage boroughs (Camden, Islington, Hammersmith and Fulham, Kensington and Chelsea, Westminster, Wandsworth) have detailed character appraisals — read yours before designing.
Design rules that consistently win approval
Matching materials: London stock yellow brick (or red brick matching neighbours) with lime mortar; natural slate or clay tile to match existing roof; timber sash windows with traditional glazing bars; cast iron or aluminium rainwater goods. Set-back additions: rear extensions should sit below the original eaves line, set back from the side elevations, with parapet walls hiding the new roof from the street. Subordinate scale: the addition should read as secondary to the host building — never taller, never wider, never more prominent. No street-facing alterations: rear-only dormers, mansards or rear-only rooflights; no PVC, no UPVC, no exposed concrete on street elevations. Lightweight glazed boxes work well behind closed-board fences but rarely on prominent street elevations. Designed-in conservation: bird and bat boxes, swift bricks, brown roofs and green walls increasingly help planning approval.
What gets refused
Front dormers in conservation areas — almost universally refused. Roof terraces visible from the street — refused unless screened. Full-width rear extensions wider than 50–60 percent of the rear elevation — often refused as overdevelopment. Modern materials (cladding, render, exposed steel) on prominent elevations — refused without strong design justification. Sash window replacements in PVC — refused; replacements must be timber sash, like-for-like. Rear extensions that exceed the depth of the existing rear closet wing — assessed sharply on light and amenity impact. Side extensions that fill the gap to a neighbour without setback — refused on streetscape impact. Roof additions that breach the existing ridge line — refused unless replicating a mansard already present on the terrace.
