The legal line between rent by room and multifamily

[Jose Mas Perez]

Hello, my wife and I are looking at house hacking next year and have a question regarding the legal line between rent by room and multifamily.

We live in Southern California where house hacking can be difficult to do if you wanted to live for free, so we are considering a rent by the room model. 

I am aware that I should, and will be seeking legal advice from a lawyer, but was curious if anyone else new the answer or had insight. 

To give you a example, would we be able to buy a single family house and separate a area off for us to live, and rent out the rest of the house by the room to others, essentially creating a faux duplex all in the same house. 

Would that make the residence a multifamily, or single family?

Any information would help, and thanks in advance.