Side return extension ideas – plus how to build one and how much it will cost

Thinking about a side-return extension? Turn a wasted outdoor space into a flexible living area with our guide, including cost, building and more.

For many homeowners, the side-return area – the pathway that runs alongside the ground floor area of the house – is a redundant space.

But by building an extension on to it, you can make your home bigger and better.

Experts at Resi explain, 'If you have alleyway space to the side of your property and are looking to create some extra room, a side return extension might just be what you’re looking for. Side returns (sometimes referred to as side infills) allow you to expand out into an alleyway, turning an unused area into much desired living space.'

kitchen with wooden flooring and dining set

(Image credit: Future PLC/ Veronica Rodriguez)

'Side returns are often applied to Victorian terraced properties as a lot of them possess alleyways in their configuration. By filling in this side alleyway, L shaped properties are squared off, creating that all important additional space.'

'The perks of a side return extension compared to other common extensions, like a rear extension, is that it tends to use up ‘dead space’, rather than the best parts of your garden. Ideal for anyone living in areas where green space is at a premium.'

So we've got the lowdown on everything you need to know about building a side extension.

How much will a side extension cost?

A simple side extension design will cost anything from £20,000 to £50,000 dependent on the area you live, how large an extension you'd like, the design complexity, which contractors you use and the building materials you want.

Extra internal work, such as adding a kitchen, and the style of the extension – for example adding glazed external doors – will affect the final figure.

What structural work is involved?

  1. A new wall is built on either the boundary of you and your neighbour's land, or solely on your side of the boundary.
  2. A roof is added (consider a fully glazed design or one with several skylights to flood the interior with light).
  3. The side wall to the existing rear room is either completely or partially knocked through. A steel frame may need to be inserted in the wall to support this new opening.
  4. A new floor is usually put in, level with the existing floor.

kitchen with white walls white cabinets and glass sliding doors

(Image credit: Future PLC/ David Giles)

Will I need an architect?

Not necessarily. Some conservatory companies and specialist builders offer a complete ‘design and build' package service, which saves paying extra fees to architects or structural engineers for drawing up plans.'

Experts at Resi say, 'For all large scale home improvement projects, we always recommend you bring an architect on board. Many people baulk at this extra expense, but the benefits of this professional, we believe, make them a great investment. However, you are under no legal obligation to hire one.'

The benefits of using an architect

Experts at Resi explain the benefits of using an architect versus going it alone with a contractor.

  • They can help guide you through each stage of the pre-construction journey
  • By handling your planning application, their expertise in this area can give you the best possible chance of success
  • Architects can maximise and customise the space your project creates, not only giving you a better living experience but also giving a better return on your investment when it comes to selling the property
  • They can help manage budget expectations and ensure you’re never caught out by the costs involved

Do I need planning permission?

Council rules changed in October 2008, so you no longer need planning permission for a ground floor side-extension under permitted development as long as the extension is only single storey, no more than 4m high and no wider than half the width of the original house.

You'll still have to comply with Building Regulations and possibly with the Party Wall Act if you're creating a new boundary wall between you and your neighbour, so speak to your local council's planning office for details.

kitchen white worktop and dark grey cabinet

(Image credit: Future PLC/ Alasdair MacIntosh)

How long will it take?

Plan for at least eight to ten weeks for the structural work, plus more for decorating the interior of the new space.

Experts at Resi explain more, 'Timings for side returns can vary, depending on the complexity of your project, whether you face any planning challenges, and if you need to resolve any tricky party wall matters.'

'However, on average, we estimate it takes around 19 weeks to get your project ready for construction, including surveying, design, planning, building regulations, and finding a contractor.'

'Once your project is onsite, construction should take between 10-16 weeks. Typically, construction will be broken down into these stages:

  • Preparation
  • Foundations and groundwork
  • Ground and low-level work
  • External and internal walls
  • Building of the roof
  • Laying down the roof covering
  • Guttering, windows, doors and render
  • Knock through and plastering
  • Finishing touches, such as electrics and plumbing
  • Final tidy up'

Who do I contact?

The Federation of Master Builders, 020 7242 7583,, has details of registered tradesmen.

Local Authority Building Control, 020 7641 8737,, can advise on applying for Building Regulations Approval.

The Institution of Structural Engineers, 020 7235 4535,, has details of engineers.

Royal Institute of British Architects, 020 7580 5533,, has a list of architects in your area.

Side return extension ideas to inspire your project

1. Install a glass wall and ceiling in the side return

kitchen with wooden table bench and bar stool

(Image credit: Future PLC/ Chris Snook)

Create a seamless indoors/outdoors feel in your side return extension by adding a full floor to ceiling window, if you have alternative doors to the garden. You could also add a glass ceiling bring more of the outdoors in and increase the light in the space to boot.

2. A spacious dining bench area with storage in the side return

dining area with wooden dining set and white flooring

(Image credit: Future PLC/ Colin Poole)

Extend out into your side return to gain more room for a long dining area. Make use of the wall space by adding a full wall storage or one of these shelving ideas to keep all your gorgeous dinnerware, glassware and more tucked neatly away.

3. Expand a small kitchen into an open kitchen-diner

open plan kitchen with dining area

(Image credit: Future PLC/ Katie Lee)

If you're "lucky" enough to be blessed with a small kitchen and a side return, why not think about knocking the side return through to create more space? You could even add a small peninsula to break up the space a little and add more light by adding in a row of rooflights in addition to bifold doors.

4. Long galley kitchen in the side return

kitchen with glass sliding doors and bar stools

(Image credit: Future PLC/ David Giles)

If you've a long, narrow space, combine a galley style kitchen with a long kitchen island with seating that can be neatly tucked away so as to keep paths to the outdoors clear and uncluttered. Add rooflights to really open up the space and keep things light and bright.

5. Create space for seating

dining space with brick walls and wooden dining set

(Image credit: Resi)

If you've already got room for a dining space in your kitchen, why not add a comfy lounge area for reading the papers on Sunday mornings or cosying up to read a book with a glass of wine at the end of the day? Add a space for a bookcase and a coffee table to make it a perfect little reading corner.

6. Add more light to the rest of your house with two glass doors

living area with dining space

(Image credit: Resi)

Use the light from the side return extension to help spread more light through the front of your home by including glass internal doors to your design and if you have the space, add two entrances to the space to maximise brightness.

7. Add a dining table and an island

kitchen with marble worktop and wooden dining set

(Image credit: Resi/HPH London)

Even if your original kitchen isn't that wide, extending out to the side return can mean you can include both an island for more kitchen storage and a family dining table too. As long as there's a pathway to the garden, you shouldn't need to compromise on either.

Jenny McFarlane
Senior Digital Editor

Jenny is Senior Digital Editor and joined the team in 2021, working across Ideal Home, Real Homes, Homes & Gardens, Livingetc and Gardeningetc. Since getting on the property ladder, her passion for interior design and gardening has taken on a new lease of life. She loves collecting and salvaging unique items (much to her other half's despair) but sniffing out stylish home bargains is her one true love. When she has a spare minute, she loves crafting, having studied textiles at university – although she hardly gets the chance with her daughters keeping her permanently on her toes.