Going underground? When can a basement be added to a ground floor flat

“Whoever’s is the soil, it is theirs all the way to Heaven and all the way to Hell”. A translation of the Latin maxim upon which a key principle of property law is based – when you buy freehold property, you own the airspace above it and the subsoil below it. However, does the principle apply to leasehold property?

In Gorst v Knight, the owner of a ground floor maisonette secured planning permission to extend a 5 foot cellar into a habitable basement. The freeholder objected the tenant’s plans on the basis the subsoil was not included in their demise.

Where a building is separately horizontally (as is the case with flats), it is the wording of the lease that will determine whether the subsoil is included in the tenant’s demise. The High Court held that the demise did not include the subsoil as the demise was expressed to include “the foundations and the void or cellar below the ground floor”. In addition, the freeholder had the benefit of a reservation to run conduits beneath the tenant’s demise.

This is a reminder of the importance, for both parties, of a clear and precise description of a demise contained in a lease, particularly where there is the possibility of future development.