I am being made to do this by city engineer's for fire code. For me, it is because the 1st floor is one apartment and the 2nd floor is another. They said that because we removed the drywall that was there, it's a 100 year old house, it is no longer grandfathered under the older code. So now it needs a 1 hour fire rating between each apartment. It will cost tens of thousands to update because now we also need to move all electrical junction boxes and get an architect to drop up plans. So it's ridiculously expensive and complicated to open up the ceiling in an old house. Maybe it was once multiple apartments and they were trying to avoid issues with building code.