Basement Conversions – A Quick Guide to Your Legal Rights

Posted By: on 28th June 2023 | Category: Residential Property

If you cannot build up, why not build down?  Converting and digging out basements is on the rise in the UK. It is a great way to add extra square footage to your property, especially when development of the current property has been exhausted.

If you are looking for inspiration as to what can be achieved when digging out a basement, at one of end of the scale, Claridge’s Hotel in Mayfair, London provides the perfect example. They have recently dug out 45,000 tonnes of clay to produce a new five storey mega basement conversion which houses a 7,000 square foot spa, amongst other amenities.

You are probably wondering whether you own the land under your building. The basic answer is yes. The Latin principle being, “Cuius est solum, eius est usque ad coelum et ad inferos,” which literally means, “whoever’s is the soil, it is theirs all the way to Heaven and all the way to Hell“. There are, however, a few caveats to this but the premise is correct.

When is Planning Permission Required to Build Downwards?

If the property already has a cellar, planning permission may not be required for the conversion to habitable living space and could be deemed to be a permitted development. However, planning permission will be required if the property is in a conservation area or is a listed building.

If you need to “dig out” the basement, planning permission is generally required. Regardless of the planning status, building regulation approval will always be required and you will probably need to enter into a Party Wall Agreement with any nearby neighbours.

The Government had proposed to begin regulating subterranean development work and to establish a code of practice for such works with the introduction of the Subterranean Development Bill. However, this it yet to become law and it seems unlikely that there will be new Primary Legislation in this area for the foreseeable future.

What if I Find a Mine or Minerals Under My Property?

Your Property title will need to be reviewed to assess whether any mines and minerals under your land belong to a third party. If so, digging out the basement could be a trespass. Were you to find resources such as gold or silver under your land, these would belong to The Crown.


If you are considering converting or digging out a basement, the Residential Property team at Coole Bevis LLP would be happy to review your title and advise you on any legal issues that you would need to consider.

Latest Articles





Lanes End House
15 Prince Albert Street
t. 01273 323231
f. 01273 820350


14 Carfax
West Sussex
RH12 1DZ
t. 01403 210200
f. 01403 241275


79 Church Road
East Sussex
t. 01273 722532
f. 01273 326347


5 The Steyne
West Sussex
BN11 3DT
t. 01903 213511
f. 01903 237053