A side return is the narrow strip of land beside the back of a terraced or semi-detached house, usually 1.5-3m wide, where the original outrigger leaves a gap. A side return extension folds that strip into the house, which is how a cramped galley kitchen becomes a bright kitchen-diner that opens onto the garden.
Side return extension or side extension? The difference matters
People use the two terms for the same job, but they describe different builds and councils treat them differently.
- A side return extension fills the original narrow gap at the rear only. The footprint gain is small, often 8-15m2, and the change to the front of the house is nil.
- A side extension builds across more of the plot, sometimes the full depth of the house. It adds more space, but it is far more likely to need full planning permission because of the width limits below.
- A narrow side return extension is the version most Victorian and Edwardian terraces end up with: a strip of roughly 1.5-2m. It sounds tight, but it is usually the difference between a kitchen you squeeze past and one you can put a table in.
Side extensions and side returns follow the same permitted development class in England, so the rules below apply to both. The wider you go, the sooner you hit the limits.
How much does a side return extension cost in 2026?
- Side return only (10-15m2): GBP 30,000-50,000
- Combined side return and rear (20-35m2): GBP 50,000-90,000
- High-spec finish with roof lantern and bifolds: GBP 90,000-130,000+
What moves the number most: the structural steels needed to hold up the wall you are removing, the roof (a glass lantern costs more than a flat roof), the glazing package at roughly GBP 3,000-8,000, and where you live. Expect the South East to add 20-30% to the same build.
Those are build costs, not drawings. Design and drawings are a separate, much smaller line, and at Arkiplan they are a fixed price agreed before we start.
Do you need planning permission for a side return or side extension?
Often not. Many single-storey side and rear extensions are permitted development in England, which means no planning application. The limits that matter, from the Planning Portal:
- A side extension can only be a single storey and cannot exceed four metres in height.
- It can only be up to half the width of the original house. This is the limit most wider side extensions fail.
- Eaves cannot exceed three metres in height within two metres of a boundary.
- Nothing can come forward of the principal elevation.
- A single-storey rear extension cannot extend beyond the rear wall of the original house by more than four metres for a detached house, or three metres for any other house. Subject to prior approval and not on designated land, those rise to eight metres and six metres.
- On Article 2(3) designated land – conservation areas, national parks, AONBs – all side extensions require householder planning permission. There is no side return exception.
An Article 4 direction can remove permitted development rights on an ordinary street too, so it is worth checking your address before you assume anything.
Those figures are the England rules. Wales has its own permitted development limits for householder extensions and they differ in the detail, so check the Welsh Government guidance rather than applying the numbers above.
If your extension is permitted development, it is still worth applying for a Lawful Development Certificate. It is the document that proves the work was legal, and the one a buyer’s solicitor will ask for.
Building regulations for a side return extension
Nearly every side return extension needs building regulations approval, whether or not it needed planning permission. The approval covers structural calculations for the steels, insulation, drainage (side returns very often sit over a drain run), fire safety and escape, and the electrical work. This is a separate process from planning, run by building control rather than the planning department.
Design ideas: making a narrow strip feel generous
- Roof lanterns (around GBP 3,000-8,000 installed) put daylight into the middle of the plan, which is where a deep terrace goes dark.
- Combine the side return with a rear extension to create an L-shape, and you get one open kitchen, dining and living space rather than two awkward ones.
- Bifold or sliding doors onto the garden. Sliders keep more glass and less frame; bifolds open the whole wall.
- Keep the kitchen run along the new wall so the old room keeps its ceiling height and the table sits in the light.
- Rooflights over a flat roof are the cheaper way to get the same daylight if a lantern is out of budget.
If you are building within three metres of a neighbour’s foundations, the Party Wall etc. Act applies and you will need to serve notice. Do it early – it is a timetable, not a formality.
The side return extension process, step by step
- Survey and design. Measure what is actually there, then design into it.
- Planning and building regulations drawings. Either a planning application or a Lawful Development Certificate, plus the technical set.
- Structural calculations. Sized steels, so your builder is pricing the real job.
- Find a builder. Get three quotes off the same drawings, otherwise you are comparing guesses.
- Build. Typically 10-16 weeks on site.
- Completion certificate from building control, which is what you hand over when you sell.
Common questions
Is a narrow side return worth extending into?
Usually yes. Two metres of width across the back of a terrace is often what turns a galley into a room, and the strip is doing nothing except collecting bins and moss.
Can I do a side extension in a conservation area?
In England, not as permitted development – all side extensions on Article 2(3) designated land need householder planning permission. It can still be approved, it just needs an application and a design that answers the conservation officer.
How long does the paperwork take?
A planning application or Lawful Development Certificate runs on the council’s clock, typically eight weeks for a householder decision, and building regulations can run alongside the build.
Do I need an architect for a side return extension?
You need drawings good enough to get permission and to build from. Whether that comes from a full architect’s service or a fixed-price drawings package depends on how much design input the job needs.
Getting your side return extension started
We work remotely with homeowners across England and Wales: a measured scan of your house, a design, and the drawings your council and your builder need, at a fixed price. Arkiplan has 18 years and 2,000+ homes granted permission behind it, with a 94% planning & LDC approval rate.
Book a free design call and we will tell you straight away whether your side return is likely to be permitted development or need an application.