A side return extension fills in the narrow gap that runs alongside the back half of a Victorian or Edwardian terrace — typically between one and two metres wide — extending the kitchen or ground floor living space outward to the boundary.

Side return extensions are specific to properties that have a side return - the narrow gap alongside the rear section of the house that runs to the rear boundary. This is a defining feature of the Victorian terrace layout, which makes it extremely common across Chiswick W4, Hammersmith W6, Fulham SW6, Chelsea SW3, Acton W3 and the wider Victorian terrace belt across West and South West London.

Side return extensions on terraced houses typically fall within permitted development for single-storey builds, subject to the standard conditions on height, materials and proximity to boundaries. Where the side return abuts a highway — which applies on some corner plots — permitted development rights may be reduced or removed. Conservation area designations, which cover significant parts of Chelsea, Fulham and parts of West London, impose additional requirements on external materials and roof treatments.

Side return extensions in London typically range from £40,000 to £65,000 depending on the length of the return, the specification of rooflights and glazing, and the extent of internal reconfiguration involved. Projects that include a full kitchen remodel as part of the extension programme will sit higher.