basement extension

Do I need planning permission for a basement extension?

Basement extensions are one of the more ambiguous projects when it comes to planning consent and unfortunately it’s not a straight yes or no. Nationally, the planning rules around forming living accommodation in basements is ever changing and under review. Local councils will also have their own rules and guidance.

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Is a basement extension classed as permitted development?

Theoretically, converting an existing basement into a living space does not require planning permission. Read specifically about basement conversions here. However, like all home extension projects that fall under permitted development, there are set of pretty rigid rules to follow. For example, if you were to include a lightwell, railings or skylight at the front of your property (or anything that affects the external appearance of your house), it’s likely that you would need to apply for planning permission.

Excavating to create a new basement which involves major works is likely to require planning permission.

Any of the other following conditions would also prevent the development from benefitting from permitted development, and would require planning permission:

  • You are creating new separate residential unit.
  • You live in a conservation area or your property is listed.
  • Your property is exempt from permitted development rights, e.g. a flat, rather than a whole dwelling.

You can read more about general permitted development restrictions for extensions here – How big can I build an extension without planning permission?


Do I need building regulations approval for a basement extension?

You will require building control approval for all excavation works or enlargements of a basement.


What other permissions are required for a basement extension?

In many cases you will need a party wall agreement with your neighbours. This includes:

  • when excavation is within three metres of a neighbouring structure
  • or when excavation would extend deeper than that structure’s foundations
  • or within 6 metres of the neighbouring structure and which also lies within an area defined by a 45 degree line from that structure.

If your property is leasehold you will need to seek freeholder permission. Most residential leases require some form of landlord permission for alterations.


Getting started

To find out whether you will need planning permission on a basement extension for your particular circumstances/property, you should always seek advice from your local planning authority. However with complex projects, it’s usually best to do this via your architect, who will know the best way to approach them and present your intentions.

Unless you are planning a straight conversion of an existing space, basement extensions requiring excavation are more complex projects than other residential extensions. Therefore it’s very important to engage the right team of experts. The first step is usually to hire an architect, who can then help you hire other necessary professionals (usually a structural engineer, and party wall surveyor) and ensure you meet the appropriate statutory obligations.


Read more about basement development from our blog:

Planning rules for basement extensions

Basement extension ideas and inspiration

How much does a basement extension cost?


Finding the right architect for your basement extension

Design for Me is a free platform to help you quickly find the right design professional for your home project. My name is Emily Barnes and as a residential architect myself, I started Design for Me after finding that talented and innovative smaller firms and individuals, who are perfectly placed to design new homes, extensions and renovations, can often get buried under the online profiles of large commercial companies.

Before Design for Me, the right architect was very difficult to find!

Once you register your project, we’ll match it with 100s of top architects in your area and beyond, and you can see who may be available and eager to work on your project straight away.


Emily  Design for Me

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