An ADU is an accessory dwelling unit to the primary home and has a permanent foundation. A tiny home can also be an ADU (typically at 400 sq ft or less in size). Most jurisdictions have limits on sizing of ADUs. In the City of Portland, the limit is 800 sq ft of livable space (not including attached garage or storage). If a tiny home is on wheels or not including a permanent foundation, it is not an ADU. We hope that helps!