Rezoning from 4-plex to 6

[Katie M Reece]

I'm purchasing a couple properties that are currently recognized as duplexes by the county. However, they already have two studios that have not been rented out, which I plan to remedy. In my area (and maybe everywhere?) the zone is the same for a duplex up to 4 units. However, these properties also have two, 2 car garages that might make the units easier to rent but they don't add much to the rent. I am wondering if I could convert them into two additional studios, but I don't know the process or how difficult it usually is to get zoned from the smaller multi-family to the larger. The area is full of apartment complexes, etc. I'm in Phoenix, AZ