Basement Planning Permission: What to Check Before You Dig

Planning a basement starts with lots of questions. What will the space be for? Will it need its own entrance? Do the neighbours know? And the big one: do you need basement planning permission at all? Here is how we answer that for clients, along with what we’ve learned from going through pre-application advice on real projects.

Do you need planning permission?

It depends on what you are doing, and in London it also depends on your borough, because each council has its own basement policies.

• Converting an existing cellar into living space, with no changes to the outside of the house, often doesn’t need planning permission. It will still need Building Regulations approval.
• Digging a new basement or extending an existing one usually does need permission in London, and several boroughs have detailed basement policies.
• Light wells, new windows, a separate entrance or anything else that changes how the house looks from outside is likely to need permission.
• Listed buildings need listed building consent for internal work as well as external.

Your first move is to check with your local council. You can find your local council on GOV.UK, and its planning pages will set out its basement policy and how long applications usually take.

Pre-application advice: what we’ve learned

Most councils offer pre-application advice: you share early proposals and they tell you how they are likely to view them. For anything beyond a simple cellar conversion, we recommend it. A few things we’ve learned:

• Ask for a written response, not just a chat. It gives you an official view of likely objections and a record of how you responded. That matters because the officer who handles pre-application advice may not be the one who decides the full application.
• Keep the first submission deliberately early. The aim is for the council to guide you on size, position and materials, not to feel they are being handed a fixed design. Detailed drawings can follow with the full application.
• Go in with a preferred version and a smaller one. If the council objects to the overall size, you already have a fallback ready rather than starting again.
• Allow time. Councils can take weeks just to offer a meeting date, so build that into the programme from the start.

It works. On a house in an Area of Outstanding Natural Beauty, going through pre-planning first meant the full application already sat within the council’s guidelines, and permission wasn’t an issue. You can read about that project in our Living Space Design of the Year finalist.

Party walls

Even if you don’t need planning permission, if you share a wall with neighbours, or you’re digging close to their foundations, you will almost certainly need to serve notice under the Party Wall Act before work starts. Leave time for it, because a neighbour can ask for their own surveyor.

If you want to see what all of this leads to, our Fulham basement extension shows a finished basement, room by room, snag list included.