Planning permission for a basement
Converting an existing cellar is often permission-free, but excavating a new basement, or adding a lightwell, usually needs planning permission because of the works and the effect on appearance.
There are two very different projects here. Fitting out a cellar you already have is largely internal work. Digging a new basement, or altering the outside with a lightwell or new access, is a major undertaking that councils treat carefully.
- Refurbishing or converting an existing cellar to living space, as internal work
- No change to the external appearance and no new residential unit created
- Keeping the space within the existing footprint and use of the home
- Excavating a new basement, which commonly needs permission due to the works involved
- Adding a lightwell, especially on a front elevation, or altering external appearance
- Creating a separate residential unit, or changing use (for example to a business)
- Areas with local basement policies (supplementary planning documents) controlling depth and size
Don't forget building regs
Basements are demanding under building regulations: structure, waterproofing (tanking), ventilation, means of escape and, for habitable rooms, natural light all have to be resolved. Our structural engineers design the retaining structure and underpinning.
Because a basement is as much a structural project as an architectural one, having both disciplines under one roof matters. We confirm whether your project needs permission, design the waterproofing and retaining structure, and produce a coordinated building control package. Start a conversation on the contact page.
Frequently asked
Do I need planning permission to convert my cellar?
Usually not, if you are simply converting an existing cellar to living space with no change to the outside of the property and no new separate dwelling. Adding a lightwell or altering the external appearance changes that.
Does digging a new basement need planning permission?
Almost always. New basement excavation typically requires permission because of the scale of works and the effect on the property and neighbours, and some councils have specific basement policies. We check local rules before designing.
Not sure where your project stands?
Checking whether you need planning permission is one of the first things we do: on the house, before any drawings. Tell us about your project and we'll confirm the route.