Rent by the room / boarding house in NoVa?

[Geo Dan]

I'm looking to buy a property to rent by the room, preferably in Fairfax County. I see that Fairfax County has overcrowding restrictions, such as no more than 4 unrelated occupants per house. Fairfax County also requires you to have a permit of some kind to run a boarding house, but I can't find any info on this. Does someone have experience with renting by the room in Fairfax County? Is this legal?