A full-width rear extension in Battersea starts with the existing rear building line and the depth of garden behind it. The 'between the commons' terraces typically have an original rear outrigger — the closet wing — set beside a narrow side return, so the back of the house steps in and out rather than running flat. A full-width extension squares that off, projecting across the whole width to a new, single rear building line. The useful question is how far that line can move: far enough to transform the ground floor, but not so far that it swallows the garden, overshadows a neighbour or reads as an over-development of a modest terrace plot.
The projection depth is the decision everything else follows from. On a Victorian terrace the defensible depth is set by the garden that remains behind the new wall, the daylight reaching adjoining rear windows and the way the extension sits against the run of rear elevations along the terrace. A depth that is unremarkable on a wide end-of-terrace house can overshadow the attached neighbours on a narrow mid-terrace plot, so the same figure is not equally available to every house. We model the extension in section against both boundaries early, so the footprint is agreed on evidence rather than optimism, and so the garden keeps a usable proportion.
Daylight is where a full-width rear differs most from a narrower addition. Because it runs the whole width of the house, the new wall stands hard against the party boundary on both sides, so its effect on the rear windows of the neighbour to the left and the neighbour to the right both come into the assessment. Wandsworth tests daylight and sunlight to neighbouring windows using the established BRE method, and a full-width extension is more exposed to those tests than a side-return infill that only touches one boundary. A carefully controlled height near each boundary, and a roof that steps down at the edges, is usually what keeps a scheme within them.
Roof form and materials decide whether the addition reads as part of the house or as an afterthought. A flat roof with a discreet parapet, a shallow mono-pitch falling away from the original wall, or a glazed lantern set into a flat roof each suit different rear elevations, and the right choice depends on the height of the existing ground-floor windows, the position of the first-floor sill above and how the extension is seen from the garden and from neighbouring gardens. On the terrace streets we detail the junction with the original rear wall carefully, and choose brick or render to sit quietly against the host, so the original elevation stays legible above the new roof.
Where the property sits within a conservation area, the back-of-terrace rhythm becomes part of the assessment. The rear elevations of the 'between the commons' streets repeat down the terrace, and a full-width extension is judged on how it reads within that pattern rather than in isolation. That rarely rules out a rear extension, but it does raise the bar on roof form, height and materials, and it makes a subordinate, well-detailed design the route through. We check whether a conservation designation applies to your street and, where it does, set out the case in the planning drawings and a short supporting statement.
From there the route is a coordinated one. We survey the house, test the projection against the daylight and amenity constraints and the terrace rhythm, and develop a design a Wandsworth case officer can support, then produce the planning drawings and, once the principle is settled, the building regulations package covering structure, drainage, insulation and the new opening between old and new. A full-width rear extension almost always bears on or excavates near both party walls, so we identify the notifiable neighbours on either side and coordinate with a party wall surveyor. Where the house has been divided into flats, freeholder consent through a Licence to Alter runs alongside the planning route.
