Single family zoned but clearly looks like a Multi-Family

[Reed Meyer]

I am currently looking at a property that is zoned as a single family but clearly looks like a multi-family residence. It has main floor with full kitchen, living room, 3 bedrooms, and bathroom and a garden unit with a full kitchen, living room, 3 bedrooms and bathroom. It has a staircase that leads down to the lower level with a door at the top that can be closed and it even has a separate entrance where you can enter the garden unit from the side of the house. Is there anyway to make this a multi-family residence or if it is zoned as a single family is that pretty much a done deal?