In the investing world on BP a lot of people talk about the BRRRR (Buy Rehab Rent Refi Repeat coined by Brandon Turner) and that goes for properties that are in bad shape at the start then get fixed up. You can build ground up, or you can convert a garage to make the unit on a single-family lot, or multifamily lot. It gives owners another option or gives investors options when they look at a property that is market value. The value of the front would be just like the value you would comp out when looking at a normal rehab project. ADUs allow you to offer market value for a home, do all the work, and then refinance the deal!