Choosing a single or double storey extension

Stuck between choosing a single storey or double height extension? Here's the lowdown.
Adam SnookResearcher & writer

Adding a single storey extension will improve your home's layout and and should increase its value. But could it be worth adding another storey while you're at it?

A single storey extension is an ideal way to create extra living space in your home, and might allow you to expand an existing small kitchen into a kitchen dining and living space. It could also give you the extra space to add a utility room, a cloakroom or boot room.

A double storey extension gives you all of the above, plus extra bedroom and bathroom space upstairs. It's definitely a more expensive option, however, the cost isn't actually double as a lot of the expensive structural work is already in place. 

Compare costs on single and double extensions and find out how much an average extension should cost per meter squared.

So what are the differences between single, double and side return extensions?

Single storey or full width extension

  • This type of extension tends to just occupy the downstairs of a property and is often added to the rear.
  • In some cases, it’s possible to extend the entire breadth of the house.
  • Most people opt for this type of extension if they have garden space they can sacrifice to add a few extra meters to their house.
  • It could also mean a second-floor extension above an existing ground floor.
  • Quite likely to have to arrange a party wall agreement that protects the neighbouring properties. Find more information on party wall agreements on our building regulations and planning page.
  • Many people opt for large folding doors to connect the indoor and outdoor space and maximise light entering the property.
  • Design can vary from flat roof to pitched roof with simple skylight windows, lantern windows to full glass roofs.

L-shape, side return or wraparound extension

  • Still a single storey extension, a side return usually refers to Victorian properties that have an often unused or underused area of garden to the side and rear of the property. Exploit the underused area by integrating it into the building.  
  • Extending into the area can create a light-filled space, often turning slim, galley-like kitchens into bright, open-plan kitchen diners with space for dining and living.
  • The process will likely involve knocking walls down to create an open-plan space. Careful consideration should be given to ceiling heights and light levels.

Double storey or multi storey extension

  • Although more expensive than a single storey extension, you tend to gain more space for your money per square meter. Find out the difference in our costs page.
  • Depending on the size, you can either create larger versions of the rooms you already have or create completely new ones.
  • Can be tricky gaining planning approval as they tend to involve a lot of work and can drastically alter the look of a property. It can seriously effect neighbouring properties too, effecting their light and view.

For a detailed summary of an average extension build timeline, head to our building an extension timeline page.

Extension types