My ceiling fell in in my rental house last night. No water damage. Who is liable for this?

My ceiling fell in last night in my rental home. The entire ceiling, insulation and everything; you can see straight up to the boning of the roof. Luckily, none of my roommates or I were home when it happened but we all came home to it. The insulation and debris covered our entire living room, stairs and hallway. My question is how should this be handled? There is absolutely no water damage HOWEVER when we looked around we noticed that the ceiling was put up with finishing nail instead of drywall screws or nails. Is this something that the landlord is liable for? We are going to be staying with friends till it is fixed so should we have to legally pay the rent?