What document should my tenant sign when they want a roommate?

[Franklyn Gutierrez]

My tenant asked for a roommate, so I informed him that I would need to do a background check and credit check. I am okay with having the roommate move in but im not sure of what type of document I should have the tenant and roommate sign. I would like the tenant to be fully responsible for rent and apartment. would it be a lease addendum?