What is a side return extension?

If you are thinking of building a house extension in London, and don’t want to compromise your rear garden space, why not consider an extension to the side of your house? This is known as a side return extension and most common in Victorian terrace houses where the original building leaves a strip of land on the side of the house making an L shaped garden.  


Of course, they can be used in any home and often they are the more cost-effective way of increasing the living area in your home.  You could even consider a wraparound extension that combines a side extension with a rear extension.  


There are usually two reasons people choose a side extension over a rear extension – space and cost. In Central London, where homes usually don’t have large rear gardens or are terraced or semi-detached, a side extension is the only way to expand the living space… Remember, as space is at such a premium in London, any addition/ extension/ expansion will add value to your property.  


One of the first questions we get asked is by homeowners is “how much does a side extension cost? The simple answer is “it depends… 

The cost of building a side return extension is dependent on a number of factors including: 


  • The size of the extension 
  • The layout of the garden 
  • Ground conditions
  • Proximity to neighbouring properties 


But just to give you an approximate idea, typically, in London, a side return extension can cost anywhere between £3,000 – £5,000 per square metre. So, for a ten metre extension, it could be between £30,000 – £50,000 (+VAT and professional fees). This does not include areas like the actual kitchen, flooring, furniture, paint, heating… anything that makes the space actually liveable. This approximate cost … and we would like to emphasise the word approximate… is for putting in foundations, building an external wall and roof, installing insulation and applying internal finishing, including plasteringSource: 


The other question we often get asked is about planning permission. “Do I need planning permission for my side return extension?” The answer is no. Side return extensions fall under permitted development. 


According to an article in, a side return extension doesn’t need planning permission as long as it satisfies certain criteria. These are: 


  • It must be attached to a house (flats and maisonettes don’t qualify).  
  • Permitted Development rights may be restricted if your home is in a conservation area. 
  • To qualify for PD, a side return rear extension must not extend beyond the rear wall of the original house by more than three metres (if it’s an attached house) or by four metres (if it’s a detached house). Until 30 May 2019, these limits are doubled for both attached and detached houses. 
  • A side return extension must be single storey (no more than four metres high) and must not exceed more than half the area of land around the original house (as it was first built or as it stood on 1 July 1948 if it was built before that date). 
  •  It must also be no wider than half the width of the original house.  
  • If the extension is within two metres of a boundary, maximum eaves height should be no higher than three metres to be permitted development. 
  • As well as satisfying these conditions, you’ll need to notify the local authority of your proposal and formally consult neighbours. If there are objections, the proposal might not be allowed, so it’s wise to seek advice before getting started. 



Like any other house extension in London, you will need to get building regulation approval and chances are that you will need a party wall agreement with your neighbour, given the proximity of properties in the central and west London areas. Under the Party Wall Act, you must give notice to your neighbours if you want to carry out any building work near or on your shared property boundary (the ‘party wall’). This must be done between two months and a year before you plan to start the work. Your neighbour then has 14 days to assess how the side return extension will affect their property and to respond in writing. 


As we have been working in the West London area for several years, we are well-versed with the different types of house extensions across the city. Give us a call if you’d like to discuss your extension plans. We can be contacted on 0208 191 7595 or email us at to discuss how we can help.  

To have a look at the kind of work we have done, why not download our free brochure? And if you need any help with managing your building project, our free project management checklist has been hugely popular.