an uninhabitable ruin

[gloria]

Is taxe d'habitation payable on a property that hasn't yet been restored? - previously used for animals/farm implements

[andyh4]

It may well depend in part on whether you have been granted change of use yet or not.

After that, the condition of the building becomes important, but just because it is not restored does not in itself mean that it is not "habitable".

[cooperlola]

This might be of interest, Gloria:

http://www.forumconstruire.com/construire/topic-52710.php

There are some legal references to the appropriate legislation which may help.  Iirc, I read somewhere on this forum that the state of the floors and roof are taken into consideration, but I may have remembered this wrongly. 

[ericd]

For exemption of Taxe d'Habitation the house has to be empty of all furnitures. This is achieved by making a declaration to the Mairie.