A successful rear extension in Parsons Green starts with the existing rear building line and the depth of garden behind it. Many of these Victorian and Edwardian terraces already carry a two-storey closet wing at the back, so the 'rear building line' is really two lines — the main rear wall and the projecting wing — and the extension has to resolve both at once. The useful question is not the maximum footprint the plot could take, but how far a single-storey addition can project across the full width before it erodes garden amenity, overshadows the house behind or reads as an over-development of the plot. We test candidate depths in section against the daylight reaching the neighbour's rear windows, the height of the existing boundary walls and the length of garden that remains, and set a projection that is both genuinely liveable and defensible when the council assesses it.
Depth versus daylight is the judgement that governs the whole scheme, and it is distinct from the side-passage question. On a terrace the neighbour that matters most for a full-width rear extension is often the one directly behind across the garden, not just the two attached on either side. A projection that reads as modest on a deep family-house plot around the green can overshadow a shorter garden nearer the parades. We model the 45-degree and 25-degree relationships to the neighbour's windows early, because the council will weigh the loss of light and outlook against the amenity your extension gains, and a footprint agreed on that evidence survives scrutiny far better than an optimistic one.
The full-width move is what separates a house extension here from a side-return infill, and the two should not be confused. Extending across the whole rear — squaring off the plan by building out level with the closet wing and then across the remaining return — gives a single wide room rather than a narrow L, and it lets the kitchen and dining space run the full width to the garden. But it also removes the light well that the original back-addition plan relied on, and it commits both flank walls to a party-wall condition rather than just the one boundary a side-return touches. That changes the daylight strategy for the retained rooms behind: we bring light back through rooflights over the deep plan and through a generous rear glazed wall to the garden, so the middle of the house does not go dark once the return is filled and the building line pushed back.
Roof form is where a rear extension is won or lost, because on a single storey the roof is the part the neighbours actually see over the garden walls and the element that governs how much daylight the addition takes from them. A flat roof with a slim upstand keeps the addition low against the neighbour's boundary and helps the daylight case; a shallow mono-pitch falling away from the party wall, or a central glazed lantern, can lift light into a deep plan without raising the mass near the boundary. Material matters too, in London stock brick to match the terrace or a deliberately quiet contemporary finish. We set the eaves and parapet heights deliberately low against the neighbouring flank walls, and detail the junction with the original rear elevation so the extension reads as a clearly subordinate addition rather than a bulky box competing with the house.
Neighbour daylight and right to light deserve early attention on these closely built plots. Hammersmith & Fulham assesses daylight and sunlight to neighbouring windows using the established BRE tests, and a well-judged section — keeping the extension low near the boundary and stepping the roof down toward it — 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 extension approaches a neighbour's rear window we flag it at the outset. On a terrace where gardens are short and windows face each other across the boundary, that early check avoids a late and expensive surprise.
From there the route is a coordinated one. We survey the house, including the closet wing and the boundary walls, test the extension against the planning and daylight constraints, and develop a design a Hammersmith & Fulham case officer can support, then produce the planning drawings and, once the principle is settled, the building-regulations package for construction covering structure, drainage, insulation and the new openings. Because a full-width rear extension bears onto or abuts the party walls on both sides, and its foundations sit close to the neighbours, the Party Wall etc. Act 1996 almost always applies; we identify the notifiable owners early and coordinate with a party wall surveyor so the notices run in parallel with the design and the consents do not delay the start on site.
