@Michael Haas  out of curiosity what does it usually take to legalize an existing unit  (lets say it was basically well constructed basement ADU,  but built a decade or more ago without any permits/etc I don't have any such situation so just a hypothetical question,   though I do have some extra storerooms at one of my properties that would be best converted to a studio unit ; but when I investigated this with the local municipality they basically wanted me to upgrade the entire building to current code standards in order to be able to finish out that space as a 5th unit.