Duplex with no permits

[John Simerson]

Hi guys this is my first post here, and am not to educated on permits or regulation so any advice is well appreciated. Long story short a friend is selling his duplex here in California to me for a good deal but the duplex in the back doesn't have permits and doesn't have its own address. Is this a big deal? Could I still rent it out as LTR? Is STR an option? Any advice is appreciated thank you!