A rear extension on a Wandsworth Town terrace begins with the existing rear building line — the back wall of the main house and the original closet-wing or back-addition that steps off it. The useful question is not how much footprint the garden could hold but how far the rear wall can move before it overshadows the neighbour, erodes usable garden or reads as an over-development of a narrow plot. On these Victorian houses the gardens are often long but the frontage is tight, so a modest, well-proportioned projection frequently outperforms a deep one at planning. We survey the back-addition, test single-storey depths in section against the daylight reaching the adjoining windows, and fix a rear building line that is both liveable and defensible before any drawing is committed. A rear extension that respects the depth already set by the neighbours, and that keeps a proportionate strip of garden behind it, tends to move through Wandsworth with far less resistance than one pushed to the limit of the plot.
The choice between single and two storeys changes the assessment completely. A single-storey rear extension is judged largely on garden impact and the daylight reaching the neighbours on either side, and it is the most common move on these terraces. A two-storey rear addition — realistic on the larger St John's Hill Grove and Wandsworth Common edge family houses — brings first-floor windows, outlook and a sense of enclosure over the adjoining gardens into play, and on an attached terrace or semi-detached pair it is far more sensitive because both neighbours share the rear boundary line. We advise early which storey height a given house and its rear relationship can carry, so the design is not committed to a submission the plot cannot support. Where a second storey is not defensible, a single storey with a well-handled roof and full-width glazing often delivers most of the space the owner wanted without inviting the objection a taller mass would draw.
Squaring off the plan is the characteristic Wandsworth Town rear extension. The Victorian back-addition leaves an L-shaped footprint with the original side gap beside it, and a rear projection that fills the return to the full width of the house turns that awkward step into a single generous room across the back. The design turns on how the new full-width rear wall meets the boundary walls on both sides, how far it projects beyond the back-addition, and whether the neighbours already extended — because a matching depth alongside an existing neighbour extension is usually easier to defend than one that projects well past it. We set the projection against what sits on either side rather than against the garden alone, and we resolve where the new full-width roof drains and how its rear wall carries the glazing that a garden-facing room wants. Getting that width right is what turns a dark rear kitchen and a redundant side gap into the single, light room most owners are actually after.
Roof form is where a rear extension is won or lost, both aesthetically and in daylight terms. A flat roof with a discreet parapet, a shallow mono-pitch falling away from the house, or a glazed lantern each suit different rear elevations, and the right choice depends on the first-floor window sills above, the height available under them and how the roof is seen from the neighbouring gardens. Keeping the extension roof low near the shared boundary and stepping it up towards the middle of the plan is often what keeps a scheme within the daylight tests while still giving the room height it needs. We detail the junction with the original rear wall so the addition reads as clearly subordinate to the host house, and we set the parapet or eaves height deliberately rather than letting the internal ceiling drive an over-tall box that a case officer or a neighbour then objects to.
Neighbour daylight and right to light deserve attention from the first sketch, because terraced houses sit close enough that a rear projection can measurably affect the windows next door. Wandsworth assesses daylight and sunlight to neighbouring windows using the established BRE tests, and a carefully judged section — controlling the height within a metre or so of the boundary and pulling the mass back from the party line — usually keeps a rear extension within them. Right to light is a separate civil matter that a planning consent does not settle, so where an extension approaches a neighbour's window we flag it early. On these tight plots it is far cheaper to resolve a daylight or right-to-light concern on the drawing board than after a scheme is submitted.
From there the route is a coordinated one. We survey the house and its rear return, test the extension against the planning, conservation and daylight constraints, and develop a rear building line and roof form a Wandsworth case officer can support. Once the principle is settled we produce the planning drawings and supporting information, then the building regulations package covering the foundations, structure, insulation, drainage connections and the new opening formed in the original rear wall. Because the extension bears on or sits beside the party walls to both neighbours, the Party Wall etc. Act 1996 almost always applies, so we coordinate the notices with the design. The result is a rear extension that adds genuine space without unbalancing the terrace or its garden.
