Quick summary
A side return extension is a popular way to create more living space by extending into the unused area at the side of a property. They’re particularly common in Victorian and Edwardian terraced homes.
A typical side return extension takes around 3–5 months to build, although the overall project timeline will also include design, approvals and preparation. Costs can range from approximately £80,000 to £200,000+, depending on the size, specification and whether you’re building a single-storey, double-storey or glass extension.
Many side return extensions can be built under permitted development rights, provided they meet certain requirements. However, planning permission may still be required, and a Party Wall Agreement may be necessary where work affects a shared wall or involves excavation close to a neighbouring property.
What is a side return extension?
A side return extension uses the often-underused strip of land running alongside a house to create additional internal living space.
Instead of extending further into your garden, as you would with a rear extension, a side return fills in space that may otherwise serve as an alleyway or narrow passage. This makes it an especially attractive option for terraced and semi-detached homes where space is at a premium.
Side return extensions can be designed in several ways depending on your property, budget and plans for the new space.
Single-storey side return extension
Typical size: around 3m x 5m
Estimated cost: £90,000–£120,000
A single-storey side return extension converts unused space beside your property into additional ground-floor living space. It can be particularly effective for enlarging kitchens and creating open-plan kitchen and dining areas.
Double-storey side return extension
Typical size: around 2m x 7m
Estimated cost: £150,000–£200,000
A double-storey side extension creates additional space across two floors. Depending on the property and planning constraints, this could provide extra ground-floor living space as well as an additional bedroom, bathroom or home office upstairs.
Side return kitchen extension
Estimated cost: £80,000–£120,000
A side return kitchen extension can transform a narrow kitchen into a wider, brighter and more flexible space. Extending sideways can make room for kitchen islands, dining areas, additional storage and improved connections to the garden.
Side return extension for a Victorian terrace
Estimated cost: £80,000–£120,000
Side return extensions are particularly popular for Victorian terraced houses, many of which were built with narrow passages alongside their rear additions.
Extending into this space can help turn traditionally narrow layouts into larger, more practical living areas without sacrificing as much garden space as a conventional rear extension.
Glass side return extension
Estimated cost: £80,000–£140,000
A glass side return extension uses features such as roof glazing, skylights and large glazed doors to maximise natural light.
This can be particularly useful because filling in a side return may otherwise reduce the amount of daylight reaching rooms towards the centre of the house.
How much does an architect charge for a side return extension?
Architect fees depend on the size and complexity of the project and the level of service you require.
Enter your postcode to get an estimate for your project.
Do you need an architect for a side return extension?
While an architect isn’t necessarily required for every side return extension, professional design support can be extremely valuable when altering the layout and exterior of your home.
An architect can help you make the most of the available space, develop the design, prepare drawings and navigate planning and Building Regulations requirements.
Having professional support early in the project can also help identify potential issues before construction begins, reducing the risk of expensive surprises later.
Read our guide to whether you need an architect for an extension to understand what an architect can provide at each stage.
How much space do you need for a side return extension?
One of the biggest advantages of a side return extension is that it can make use of a relatively small area.
Rather than extending deep into your garden, the extension fills the unused space beside the existing property. Even a narrow side return can make a noticeable difference to the width and usability of a kitchen or living area.
Exactly how much space you can use will depend on your property’s existing layout, boundaries, planning constraints and the design of the extension.
Do you need planning permission for a side return extension?
Not always. Some side return extensions can be completed under permitted development rights, meaning a full planning application may not be required.
Whether permitted development applies will depend on factors including the property’s location, the size and height of the proposed extension and whether the property is listed or within a conservation area.
As a general guide, relevant requirements can include whether the extension:
- Sits to the side of the house and does not front a highway
- Uses materials similar in appearance to the existing property
- Does not result in buildings covering more than 50% of the land around the original house
- Is no wider than half the width of the original house
- Is no more than 4m high, with additional height restrictions close to boundaries
- Has eaves and a ridge that do not exceed the height of the existing house
Permitted development rules are subject to specific conditions, and rights can also be restricted or removed for individual properties.
If you’re unsure whether your side return extension needs planning permission, book a free consultation with our team to discuss your project.
Do you need a Party Wall Agreement for a side return extension?
The Party Wall etc. Act 1996 may apply where extension work affects a shared wall, boundary or involves excavation close to a neighbouring building.
This is particularly relevant for side return extensions to terraced and semi-detached houses, where new foundations may be constructed close to neighbouring properties.
Depending on the work involved, you may need to serve formal notice on affected neighbours before construction begins. Excavations within 3 or 6 metres of a neighbouring building can also fall within the Act depending on the depth and position of the proposed foundations.
It’s worth investigating Party Wall requirements early so they can be factored into your project programme.
Find out what steps your project may require with a free advice call with one of our consultants.
How long does a side return extension take to build?
A typical side return extension takes around 3–5 months to build, although every project is different.
The construction period will depend on factors including the size and complexity of the extension, structural work, specification, access to the property and unforeseen site conditions.
Remember that the complete project takes longer than the construction phase alone. You’ll also need to allow time for architectural design, planning or permitted development checks, Building Regulations approval, Party Wall matters where applicable, contractor selection and preparation.
Is a side return extension worth it?
For homes with unused space alongside the property, a side return extension can be an effective way to create a larger and more practical layout without taking a significant amount of space from the garden.
There are three particularly useful benefits.
More living space. A side return can turn an unused alleyway into valuable internal floor area. It could become part of an open-plan kitchen and dining room, additional storage, a utility area or simply provide more breathing room within the existing layout.
More natural light. Thoughtful side return extension design can dramatically improve daylight. Rooflights, glazed roof sections, internal glazing and large garden doors can all help bring natural light deeper into the property.
Potential added property value. Creating additional usable floor space and improving the layout can make a property more attractive to future buyers. However, the value added will depend on the quality of the extension, the property itself and the local housing market.
Start planning your side return extension
A well-designed side return extension can transform unused space into a brighter, wider and more functional home.
The key is understanding what’s possible before committing to a design — including your likely side return extension cost, planning requirements, Party Wall considerations and construction timeline.
Explore your side return extension project
Planning a side return extension involves more than choosing a layout. Explore BetterPlanHomes project guidance to understand the key planning, cost, design and practical considerations before committing significant money.