Side Return Extension Cost
The side return is the strip of yard beside the back room of a Victorian or Edwardian house. Roofing it over and taking out the wall beside it turns a narrow galley into a kitchen the full width of the plot. It adds little floor, so it is priced less by the square metre than by the steel, the glass and the neighbour.
£22,000to£28,500
For a side return 1.8 m wide and 6 m long (11 m²), outside London. Building work at a standard to good finish, with VAT. A guide, not a quote.
Side return prices by size
Building work only, including VAT, at 2026 national rates. Most side returns are built in London, where the same 11 m² costs about £26,500 to £40,000.
| Size | Floor area | Standard to good finish | High finish |
|---|---|---|---|
| 1.5 m by 5.5 m | 8 m²A short, narrow passage | £16,000 to £21,000 | £22,500 to £24,000 |
| 1.8 m by 6 m | 11 m²The usual terrace side return | £22,000 to £28,500 | £31,000 to £33,000 |
| 2 m by 7 m | 14 m²A long back addition | £28,000 to £36,500 | £39,000 to £42,000 |
| Wraparound | 22 m²Side return plus 3 m across the back | £39,500 to £57,000 | £57,000 to £66,000 |
Where these figures come from
- Planning Portal: planning permission for extensions
- HMRC: Buildings and construction (VAT Notice 708), for the 20% rate on extensions
- GOV.UK: Fees for planning applications in England
- GOV.UK: Permitted development rights for householders, technical guidance
- GOV.UK: Building regulations approval
- GOV.UK: The Party Wall etc. Act 1996, explanatory booklet
Why a small extension carries a large price
A side return has three costs that do not shrink with its size. The long wall of the back addition, which holds up the floor and roof above, has to come out and be replaced with steel. The new outer wall goes up on or beside the boundary, so the foundations are dug by hand next to the neighbour's house. And everything, from the spoil to the steel beam, travels through the front door and along the hall, because a terrace has no other way in.
That is why our figures for anything under 15 m² start from the upper half of the national range. Treat a quote that comes in well below the table with care: it may have left out the steel, the drains or the making good inside the house.
The roof: glass, solid or both
The classic side return has a fully glazed pitched roof, which keeps daylight in the middle room of the house. It is also the most expensive way to cover the space, and the hardest to keep cool in July. A solid flat roof with two or three rooflights costs less, insulates better and still lights the plan.
Building regulations take a view as well. Approved Document L limits the glazing in an extension to roughly a quarter of its floor area plus the area of any windows and doors the extension covers up. Go beyond that and your designer has to show by calculation that the whole room loses no more heat than a compliant one would, which usually means better glass or more insulation elsewhere.
Planning for a side return
In England a single-storey side extension is permitted development if it is no more than 4 m high and no wider than half the width of the original house, and a side return nearly always meets both tests. Within 2 m of the boundary, which a side return always is, the eaves must stay at or below 3 m.
Two catches. Side extensions are not permitted development in conservation areas, and many streets of Victorian terraces are in one, so check the council's map before anything else. A householder application costs £548. And a wraparound, which joins the side return to a rear extension, is measured as one extension. It is usually wider than half the house, so it fails that test and needs a planning application. In Scotland the limits differ and a building warrant is needed in every case.
The neighbour and the party wall
Almost every side return triggers the Party Wall etc. Act 1996. You must give the adjoining owner written notice at least one month before building a wall at the boundary or digging foundations within 3 m of theirs, and two months before cutting into a wall you share. They can consent, or dissent and have a surveyor appointed at your expense.
Budget £700 to £1,500 per neighbour for that, with one surveyor agreed by both sides (more if each side appoints its own), and talk to the neighbour before the notice lands. A new wall built astride the boundary, with their written agreement, gives you a few more centimetres of kitchen and gives them a wall to build against later. Without agreement, the wall sits wholly on your side.
Drains in the passage
The side passage is where the old house put its drains. Expect at least one gully, often a soil stack, and in many terraces a shared sewer with an inspection chamber. All of it has to be rerouted or sealed under the new floor with a recessed cover, and a shared sewer needs a build-over agreement from the water company. Ask each builder to lift the covers and price what is there, not what they hope is there.
Side return costs, answered
How much does a side return extension cost in London?
For the usual 11 m² side return, allow about £26,500 to £40,000 for the building work with VAT, against £22,000 to £28,500 nationally. The kitchen, the design fees and any party wall surveyor are on top, so all-in budgets in London commonly pass the top of that range.
Is a side return extension worth it for so little floor?
It is bought for width, not area. A 1.8 m passage added to a 2.7 m galley makes a room 4.5 m wide, enough for an island or a table beside the units. If the back room is already wide, a short rear extension may give more for the same money.
How long does a side return take to build?
On site, about as long as a larger extension, because the structural work is the same and access is slower. Add the party wall notice period before the start.
Other cost guides
- Kitchen extension costThe main guide, the price board and the calculator.
- Rear extension costThe straight extension across the back of the house, by depth and width.
- Small kitchen extension costJobs under 15 m², and why they cost more per square metre.
- Kitchen diner extension costKnocking through and extending to make one family room.
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