Do I need planning permission for a basement?

Basement conversions and excavations have increased significantly in the last decade as more home-owners explore new and exciting underground options.

Basements are particularly suited to those living in urban areas where there isn’t much scope for outward extension – digging down seems like the obvious solution.

The popularity of basement construction in London means planning has become quite political in recent years with many London boroughs responding and acting accordingly by tightening up the rules. For example, Kensington and Chelsea was the first borough to introduce a basement policy citing that basements could not take up more than 50 percent of the garden and must not contain light wells or railings to the front or side of the property which could seriously harm the appearance and character of the locality.

The planning regime covering the creation of living space in basements is evolving and under review so if you’re thinking about building a basement, the best bet is to check with both your local authority and the planning department before commencing any works.

However, as a rough guide, here are the current guidelines:

1. Basement conversions

If there is already an existing basement or cellar at your property, it is unlikely that you will need permission to convert it into living space. However, if the conversion will alter the external appearance of the residence – for example, by adding a light well, then planning permission would need to be sought. Equally, the basement must not be a separate unit and its usage must not be significantly changed.

Listed buildings are treated differently and you will require listed building consent if you want to make changes to both the external or the internal fabric of your home.

To convert an existing basement, the space will usually require waterproofing and additional ventilation. If not already present, electrics, heating and plumbing will need to be installed, depending on what the space is to be used for.

2. Basement excavations

Excavating to create a new basement which involves major works, a new separate unit of accommodation and / or alters the external appearance of the dwelling, is likely to require planning permission. However, such is the popularity of basement excavations that a High Court ruling has granted basement excavations can be carried out under permitted development rights.

Even under permitted development, there are still limits as to how far you can dig – you can extend your house downwards under permitted development rights as long as it is just one storey and doesn’t go beyond three metres from the back wall of your property. In addition, you must leave at least seven metres between the end of your basement and the boundary of any neighbour opposite. If you want to dig out anything different to this, you will need to seek full planning permission.