Reader question: I want to build a treehouse for my grandchildren ready for when they visit us in summer. Are there rules about this, do we need any kind of permit?
For this question we are taking a treehouse to mean a fairly rudimentary structure built by yourself (or at least not professional construction workers!) that people can rest and play in, as opposed to a substantial piece of accommodation.
In the case of the latter, for example somewhere suitable for people to sleep, construction must follow the usual building and planning laws and such constructions are classed as habitations légères de loisirs (HLL), or light leisure dwellings.
This is more likely to apply, for example, to accommodation found in forest holiday parks.
In the case of building a simple treehouse not intended for sleeping in or renting out, rules are much more relaxed.
We are presuming here that the structure is only situated on your private property and not in a shared or public space.
Whether or not planning permission is needed will then depend on the size of the structure:
A treehouse with a floor surface area of less than 5m² does not require any authorisation.
A treehouse with a floor surface area of 5-20m² will need a declaration of work (déclaration préalable de travaux) to be submitted to the mairie before construction. With this tacit approval can be considered given if you do not hear back after a month (or two in some protected areas)
A treehouse with a floor surface area greater than 20m² requires planning permission (permis de construire) to be requested from the local mairie and approved before construction starts.
If you are not sure about any points, you should contact your mairie before construction, but in the case of building a treehouse for your children to play in, it is highly unlikely the floor surface will reach above 20m².
If your land is located in a protected area (secteur protégé) or natural zone (zone naturelle), rules may be slightly different, although these changes are usually directed towards construction of HLL’s and not to private treehouses like the one you are planning.