[alistairSH]

Depends on jurisdiction. Some places explicitly allow ADUs, but I don't know what building specs they require.

Many pre-fab tiny-homes are just mobile homes with trendy marketing material. This is where a lot of the issues come from with tiny homes - mobile homes are frequently banned in nicer suburban/urban areas. They're built to different codes than build-in-place homes as well (not a bad thing, necessarily, just different code written by a different organization).