Planning permission for a caveman?

The following question could have been asked 200,000 years ago but surprisingly it was formulated a few weeks ago. This is a good opportunity to broadly define the authorisations required to carry out works on any properties in France.

Question - I would like to renovate an ancient troglodyte cave to become a second home. Do I need to provide a declaration prior to works (déclaration préalable de travaux), request planning permission or nothing at all?

Reply - The new planning regulations are silent on this point, but under the old regulations, control of the external appearance of buildings led the Administrative Court of Appeal of Bordeaux to require a planning permission for the creation of doors and windows and the construction of a front wall outside troglodyte caves.

Presumably, if the appearance is modified by the installation of doors and windows, a déclaration préalable is required. If, in addition, there is construction of a wall visible from the outside, planning permission should be sought. However, if the external appearance of the cave is not changed, no formalities should be required. For instance, the installation of a mailbox is not considered as changing significantly the appearance of the property.

Local rules may also apply under certain circumstances so it is better to check carefully.