Wandsworth Council's Planning Applications Committee has approved plans for a single-storey rear extension, a two-storey side extension, and a rear mansard roof extension at 3 Southdean Gardens, SW19 6NT. The decision was made despite objections from neighbours who raised concerns about overdevelopment, the scale and massing of the proposed extensions, and the impact on their outlook, daylight, sunlight, and privacy.
The committee heard that the applicant had made several amendments to the original proposal in response to these concerns. These included reducing the height of the eaves on the western side of the single-storey rear extension by 0.2m, altering the rear elevation to a pitched roof on the western side, and amending the two-storey side infill extension to have a chamfered edge, reduced eaves height by 0.5m, and a 1.7m deep section angled 25 degrees away from the neighbouring property. Additionally, the rear roof dormer was changed to a mansard form with fenestrations within dormers, and inconsistencies in measurements were addressed. First-floor western side elevation windows were also amended to be obscure glazed.
Council officers concluded that the proposed development, despite its scale, would remain subservient to the host property and would not cause unacceptable harm to the amenities of neighbouring properties or the character of the area.
Defining 'Subservient' and 'Unacceptable Harm'
For the single-storey rear extension, officers determined it would remain subservient due to its proportional scale and form relative to the host property, its appropriate siting away from the rear boundary ensuring a substantial depth of the original rear garden remained free of buildings, and its concealment from the public realm. The two-storey side extension was considered subservient as it did not exceed the height of the existing flank wall towards the front and remained subordinate to the overall scale and form of the existing building. Amendments, including a chamfered edge and angled section, further reduced its perceived scale and massing. The rear mansard roof extension was considered acceptable as it was set down from the main roof ridge and had pitches to the side and rear elevations, remaining subordinate to the site and surrounding area. The pitched roof above the front bay and porch was deemed modest and acceptable in scale, complementing the host property.
In the context of neighbour amenities, 'unacceptable harm' was assessed based on policies that consider harm through unacceptable loss of daylight/sunlight, increased overshadowing, loss of outlook, privacy, increased sense of enclosure, and visual intrusion. For the single-storey rear extension, while some additional overshadowing and increased sense of enclosure were noted for neighbouring properties, these were deemed not to be to an unacceptable degree, and satisfactory outlook and privacy were maintained. The two-storey side extension was assessed to have limited perceptible additional enclosure and no material perceptible impact on outlook. The rear mansard roof extension was unlikely to cause significant loss of daylight/sunlight or outlook. The pitched roof at the front was considered to have no undue impact on outlook or sense of enclosure. Overall, the proposal was considered not to cause unacceptable harm to neighbour amenities.
Conditions of Approval
Conditions have been attached to the approval, including requirements for materials to match the existing building. Specifically, the two windows in the western side elevation at first-floor level of the proposed infill extension are to be obscure-glazed and non-opening, unless any opening element is positioned more than 1.7 metres above the internal floor level. This obscure glazing is to be retained thereafter. The proposed obscure-glazed windows and screened terrace were assessed to not cause harmful views or an unacceptable level of overlooking.
Further details on the planning application can be found in the Public reports pack for the Planning Applications Committee meeting on 17th September 2026.