Double Storey Side Extension


If you are planning to build a double storey extension, you are not alone. There are lots of good reasons why you might want a bigger house: your family is growing, you are working from home a lot more, you need enough room for your hobbies… or you simply want some more space. If you want more room but don’t want to move, you’ll be considering a house extension. And if you want that extension to add a substantial amount of extra space, then what you might need is a double storey extension. 


So we’re going to take you through what you need to know about two storey extensions, from the very basics to the planning rules, picking a builder and – because it’s something you’ll be asking from the start – the cost.

What is a Double Storey Home Extension?

A double storey home extension, simply put, is where you add an extension to your house and then add an additional floor to that extension. They are sometimes called ‘two storey extensions’. 

You may also have an existing single storey extension and wish to build a first-floor extension over the existing one, which would give you a double storey house extension.

A two storey extension is a great way to add another upstairs bedroom to your home and create space downstairs for a larger kitchen, additional bathroom or whatever else you might want or need.

Adding a Double Storey Extension to Rear

To begin with, homeowners will often extend their houses to the rear. Many houses in the UK have spacious back gardens and if you’re looking to increase the size of your home, it’s the most obvious land to use. 

One advantage is that this won’t change your house’s facade, which will normally please the council. And, as many houses are wider than they are deep, the end result is a more square-shaped building with neat rooms. 

Adding a Double Storey Extension to the Side

If you don’t live in a terraced house, you can then add a double storey extension to the side of your property – either using permitted development rights (if what you want to do qualifies) – or planning permission. 

The good news is adding two storey extensions to the side of your house will make your house wider, which will in return enable you to enlarge your kitchen and living area or add additional bedrooms.

Alternatively, if you have enough space on one side of your property, you might even consider building a double storey side extension to create a new dwelling house.

Why are Two Storey House Extensions so Popular?

There are a couple of reasons. Let me explain…

Firstly, it’s cheaper for the amount of additional space. The amount you are going to spend on foundations and the roof will be roughly the same whether you add one storey or two. 

Secondly, you’ll get more room. If you’re planning on having a child, they’ll need a bedroom and you can combine this with a downstairs study or an additional bathroom to help counter the needs of a larger family.

Permitted Development Rights for Two Storey House Extensions  

Permitted development rights mean that you can make some changes to your house without applying for planning permission. As a general rule, it makes things faster, cheaper and easier. 

Unfortunately, permitted development rights don’t usually apply to most double storey house extensions, but there are some circumstances where they can come into play. For this to happen, your proposed work needs to meet the following criteria:

  1. The double-storey extension should not be wider than half of the original house
  2. The double-storey extension cannot be higher at the eaves than the existing eaves, or the roof of your double-storey extension should not be higher than the roof of the original house
  3. If the double-storey extension comes within two meters of the land boundary then the eaves cannot be taller than three meters
  4. If your house faces directly onto a street, you cannot extend it forwards
  5. The double-storey extension cannot also include any balconies, verandas, raised platforms, microwave antenna, chimneys, or involve any alteration to the existing house’s roof. 
  6. The materials used on the outside of the new double-storey extension should match the materials used on the outside of the existing house
  7. Similarly, the roof pitch of the double-storey extension should match the roof pitch of the original house as closely as possible.
  8. The land used for the double-storey extension should not be within seven meters of any land boundary or extend beyond the rear wall of the original building by more than three meters 
  9. If you’re building a side elevation and want to put a window on the first floor, it should be obscure-glazed and non-opening unless the openable part is higher than 1.7 meters from the floor

Here’s the most important part: You will not qualify for permitted development if you want to build a double storey extension to the side of your home, or if you live in certain protected areas (eg, a conservation area, an area of outstanding natural beauty or a national park).