According to experts, Treehouses have no foundation and are not accessory buildings or buildings.  Under most state and country regulations, they are not defined and do not exist.

Home > Living in.. > Living in Special Dwellings > Living in a Tree House Read a Question about Living in a Tree House Question.. Asked on Thursday, September 19, 2002   ..from Save Our Treehouse about Living in a Tree House Subject: Re: Save Our Treehouse   Thanks for the help. How do you define a foundation? Does the base of the treehouse count as a foundation? The law that they have used against the treehouse does not define foundation. www.SaveOurTreehouse.com Answer.. Answered on Saturday, September 21, 2002   ..from erikerak on Re: Save Our Treehouse Generally, a building is materialised by the space it occupies on the ground. It will mostly stand on a solid foundation. In the countries I am familiar with, building permits also depend on how the foundation are made. A shed can be tolerated without permit when it's foundations are not in concrete. The construction is considered to be as provisional as setting up a tent. According to the rules I am familiar with, a treehouse does not have any existance because it doesn't occupy any surface on the ground.

..from erikerak on Save Our Treehouse Rules and regulations are so different from one country to the other. In several countries I have been living in, a treehouse simply doesn't exist because it doesn't have any foundation. The only concerns are not to hurt anybody or anybody's privacy.