The way I understand it, some streets are zoned for single-family residences only. This might not be the case in Palmer Woods, since some of those properties already include servants' quarters, guest houses, and such. But in many regular, middle-class neighborhoods, you can't buy a large house and chop it up into rental units unless the area is zoned for multi-family residences. I am also not sure if a retreat for addicts counts as a residence or a medical business. I suppose it would be akin to a nursing home? But you can't just put a nursing home on any residential street, either.