The Online Community for Tiny Living and the Tiny House Summit
The State of Washington has decided that THoWs are "Park Models" and as such fall under their jurisdiction. I personally think that is the right decision. They are certainly not RV's
The only change we as group would need is for the states to make them habitable year round.
The ANSi code 119.5 gives enough guidance to build a safe Tiny House.
The state system for oversight of construction of Park Models is designed for manufacturers, but they are "usually" open to owner builders. There are also third party inspection programs available
I hope this helps.
There is also a movement to have an addendum to the International Residential Code (IRC)
This would allow smaller Ground Bound homes.