Rent a room vs Roommate?

[Dave Garlick]

I recently found myself living alone in a fairly large house. I decided to look into house hacking and renting out the rooms upstairs. I called my city office to ask if there were any permits or inspections that needed to be done before renting. I was told flat out that you cannot rent out rooms. 

So, is there any legal difference between getting roommates vs renting out a couple of rooms? I see rooms listed for rent in the same town online. Not sure how to approach this. Has anyone run into townships that do not allow renting out rooms?