A successful rear extension in Hammersmith starts with the existing rear building line and the garden behind it. The area's Victorian terraces are typically narrow-fronted with modest back gardens, and many retain an original rear outrigger — the projecting back-addition wing that carried the old kitchen or scullery — so the existing rear elevation is rarely a flat wall to begin with. The useful question is not how big an addition the footprint could take but how far it can project past that stepped rear line before it erodes garden amenity or overshadows the house next door. We test single-storey depths in section against the daylight reaching neighbouring rear windows, the position and height of the boundary walls and the length of garden that should remain usable, and we set a projection that is both liveable and defensible when a case officer assesses it.
Full width is what distinguishes a rear extension from its side-return cousin. Where a side-return scheme infills only the narrow alley beside the original outrigger, a rear extension pushes the entire back elevation out onto the garden, spanning flank wall to flank wall and squaring off the plan behind the house. That full-width form is more generous but also more sensitive: it presents a continuous new face to both neighbours at once, and on a terrace the 45-degree daylight lines drawn from adjoining rear windows often control how deep the addition can go. We frequently step the extension down in height or set it in from a boundary near its outer corner, so the depth is held where the room needs it without stealing light from the neighbour or losing the width across the middle. Getting that balance right at sketch stage is what keeps the scheme out of a refusal.
The single-storey addition is the realistic default on the terraced stock. A two-storey rear extension — which brings first-floor outlook, overlooking and a greater sense of enclosure over a neighbour's garden into play — is far harder to justify on a tightly packed Victorian terrace, where the upper addition would sit almost on top of the neighbour's own rear windows. We treat it as an option mainly on the grander early-Victorian houses around St Peter's Square or the larger riverside period houses near Lower and Upper Mall, where the plot depth and the gap to neighbours can genuinely carry the extra storey. On the standard terrace we more often win the same space by combining a full-width single-storey rear addition with a reworked ground-floor plan, and we advise early which height a given house and garden can support before any drawing is committed.
Daylight and right to light deserve attention from the outset because terraced houses sit close enough that a full-width rear extension can materially affect a neighbour. Hammersmith & Fulham assesses daylight and sunlight to neighbouring windows using the established BRE tests, and a well-judged section — keeping the height down near the boundary and stepping the roof away from the party wall — usually keeps a scheme within them. The room that suffers most next door is often a kitchen or garden-facing window on the same side as the new flank, so we model that relationship deliberately. Right to light is a separate civil matter that a planning consent does not resolve, so where the extension approaches a neighbour's window we flag it early rather than let it surface late in the build, when it is far more expensive to design around.
The roof form is where a rear extension is won or lost against a Victorian terrace. A flat roof with a discreet parapet, a shallow mono-pitch falling away from the party wall, or a glazed lantern or rooflights set into the slab each suit different houses, and the right choice depends on the sill and head heights of the existing rear windows, the level of the floor above and how the addition is seen from the garden and from neighbours' upper floors. Because the extension so often extends off an existing outrigger, we also resolve how the new flat roof meets the older pitched or lean-to roof of that wing. In a conservation setting we keep the roof low and the addition legibly subordinate to the original rear wall, detailing the junction so the new work reads as an addition rather than a competing volume.
From there the route is a coordinated one. We survey the house and garden, test the full-width projection against the planning and daylight constraints, and develop a rear extension that a Hammersmith & Fulham case officer can support, then produce the planning drawings and, once the principle is settled, the building regulations package that covers structure, drainage, insulation, ventilation and weathering for construction. Opening up the back of the house needs a beam to carry the original rear wall, which a structural engineer designs, and where the extension crosses or diverts an existing drain the run is resolved on the drawings rather than on site. On the closely built terraced plots typical of the area the Party Wall etc. Act 1996 almost always applies on at least one flank, so we coordinate the notices with the neighbours in parallel. The result is a rear extension that adds real ground-floor space without unbalancing the terrace or its garden.
