Our city has no restrictions at all if the structure is not touching the ground. I asked if I could run power to it and they said "no" but other than that I am limited only by what the tree can accommodate, which I guess they view as all the limiter they need. The City reps did not give treehouses any special designation such as temp structures. If it touches the ground, the height limit is 12 feet.
Dennis Kane, 2007
This is one of the best planning arrangements for a treehouse builder. The only remaining concerns are to avoid causing an eyesore or invading the privacy of nearby properties - both of which can be easily accounted for in a good treehouse design.