Side return extensions: how they work

The short answer

A side return extension fills the narrow strip of garden that runs alongside the back part of many terraced and semi-detached houses, usually beside the kitchen. Building across that strip widens the room behind it, often turning a galley kitchen into a proper kitchen-diner. It is a single-storey extension, typically with a sloping or glazed roof so that light still reaches the house, and it usually sits on or close to the boundary with the neighbour.

Which houses suit one

The classic candidate is a Victorian or Edwardian terrace with a rear outrigger: the narrower back section containing the kitchen, with a passage between it and the neighbour's wall. Some 1930s semis have a similar layout. The gain in width may look small on paper, but because it joins an existing room it changes how the whole ground floor works. Where the garden is deep enough, a side return can be combined with a rear extension to make a wrap-around.

Boundaries and party walls

Because the new wall often sits on or next to the boundary, the Party Wall Act usually applies. You serve notice on the neighbour before work starts, and they can agree or appoint a surveyor. Gutters and roof edges must not overhang their side unless agreed. Where an old boundary wall is being replaced or built up, its ownership needs to be clear before anyone touches it.

Planning and Building Regulations

Side extensions have their own permitted development limits, including width and height, and a side return that also extends to the rear may need to be assessed against both sets of rules. Many side returns go in under permitted development; others, particularly in conservation areas, need a planning application. Building Regulations cover the foundations, structure, drainage, insulation and fire separation near the boundary.

Roof and light

The biggest design question is light. Filling the passage removes the window that used to light the middle of the house, so most side returns have a glazed or partly glazed roof, or a pitched roof with a line of rooflights along the side. The roof usually slopes down towards the boundary to keep the wall height low for the neighbour. A flat roof with a long rooflight is another option where height is limited.

How the build is done

Work starts with clearing the passage and checking drains, which often run along this strip. Foundations are dug along the boundary line and the new wall is built, then the floor slab. The old side wall of the outrigger is removed in stages, with steel beams or posts carrying the rooms above. The roof goes on, glazing is fitted, and the space is joined to the existing kitchen. Access can be tight, so materials may have to come through the house or over the garden.

Common mistakes

Leaving the party wall notice until the builder is booked, which delays the start. Designing a solid roof and losing daylight in the middle of the house. Ignoring the drain run in the passage. Not thinking about how the floor level and threshold meet the existing kitchen.

About us

D & A Brickwork & Building is a family-run firm based in Bidwell, Dunstable, with more than 26 years of building experience. Our bricklaying is NVQ Level 2 qualified, we are Federation of Master Builders members and fully insured, and estimates are free after a visit.

Side extensions are part of the extension work we build, from foundations and brickwork through to the roof and the opening into the house.

Questions people ask