A rear extension in Barnes starts with the existing rear building line and the depth of garden behind it. The village cottages around the pond, the terraces off Church Road and the Edwardian houses behind the Common vary in plot size, and where the garden runs deep behind the house it can tempt an ambitious footprint, but the useful question is how far the addition can project before it erodes garden amenity, overshadows an attached neighbour or reads as an over-development of the plot. We test the projection in section against the daylight reaching neighbouring windows, the position of boundary walls and any mature trees, and set a depth that is both genuinely liveable and defensible when a Richmond upon Thames case officer assesses it. What the neighbours on either side have already built at the back matters here too, because a projection reads very differently against an unbroken run of original rear elevations than it does where similar additions already exist, and we survey that context before proposing a depth.
The choice between a part-width and a full-width rear extension changes the whole assessment. A full-width addition that runs the entire back of a cottage or terrace gives the most usable space, but it also builds hard up to both boundaries and removes the outdoor gap on either side, so its massing, roof and the loss of that open ground are scrutinised more closely than a narrower addition set in from a boundary. On a terrace the flank walls of the extension usually meet the party walls with the houses on both sides, which is where the neighbour relationship — and the party wall process — becomes central rather than incidental to the design. A part-width addition set in from one boundary keeps a strip of garden open beside it and softens the impact on the neighbour that side, and on some Barnes plots that restraint is the difference between a scheme a case officer can support and one that reads as an over-development, so we weigh the extra floor area of going full width against the amenity it removes.
On the larger detached and semi-detached villas along Castelnau a two-storey rear extension can be realistic where the cottages and terraces could only carry a single storey. Adding a first floor at the back changes the assessment entirely: it brings first-floor outlook, a sense of enclosure over a neighbour's garden and potential overlooking into play, and it is far more sensitive on a semi-detached pair where the two houses share a boundary and a roof line. We advise early which storey height a given villa and its plot can actually carry, because designing a two-storey scheme that the plot cannot defend wastes time that a single-storey addition would not. Where the upper storey is realistic, the section is designed to hold the first-floor windows away from the boundary and to keep the new roof below the original ridge, so the addition still reads as subordinate to the villa rather than as a second house grafted onto the back.
Roof form and materials are where a rear extension is won or lost against a Barnes period house. A flat roof with a discreet parapet, a shallow mono-pitch tucked below the original eaves or a glazed rooflight each suit a different host building, and the right choice depends on the existing rear elevation, the window pattern above and how the addition is seen from the garden. On the stock brick terraces and rendered cottages here we consider whether matching London stock brick, picking up render or introducing restrained contemporary glazing best sits against the original, and we detail the junction with the old wall so the extension reads as clearly subordinate to the house rather than competing with it.
Neighbour daylight and right to light deserve early attention because Barnes houses, particularly the terraces and the cottages around the pond, sit close enough for a rear extension to affect the property next door. Richmond upon Thames assesses daylight and sunlight to neighbouring windows using the established BRE tests, and a well-judged section — holding the height down near the boundary and stepping the roof away from a neighbour's window — usually keeps a scheme within them. Right to light is a separate civil matter that a planning consent does not resolve, so where a full-width or deep rear addition approaches a neighbour's window we flag it early so it is addressed rather than discovered late.
From there the route is a coordinated one. We survey the house, test the rear extension against the planning, conservation and daylight constraints, and develop a design a Richmond upon Thames case officer can support, then produce the planning drawings and, once the principle is settled, the building regulations package covering structure, drainage, insulation, ventilation and fire. On the closely built terraces and semi-detached villas typical of SW13, the Party Wall etc. Act 1996 usually applies where the new work meets a shared boundary, so we identify the notifiable neighbours early and coordinate with a party wall surveyor. The result is a rear extension that adds real, connected space without unbalancing the house or its garden setting, and we are candid throughout that no consent can be guaranteed before it is assessed.
