Planning permission for basements
Converting an existing cellar falls under permitted development, as long as it doesn’t change the external appearance of a home – if you wanted to add or enlarge lightwells, for example, then a planning application would be necessary.
In reality, many cellars are little more than coal-holes with inadequate headroom that do not run the full length of the house.
In order to make them into wow-factor rooms it is necessary to excavate down and out, underpin, build new structural supports and foundations, and waterproof the space. This level of work will require permission – as will excavating any basement from scratch.
The planning rules regarding basements are currently under review, so it’s essential to contact your local authority beforehand to find out how amenable it is to a subterranean building project.