There are clips to attach to the wall that actually hold the ceiling drywall. Then the ceiling floats over that area. Or in my case it was down a hallway (walls on both sides with a 4 ft wide hallway,) Went up and put studs across the hallway that were attached to the walls. Then screw into that for ceiling drywall. Remove screws/ nails on ceiling that are screwed into the roof truss. Finally that solved my son's truss uplift issues. His was right in the middle of the house and would lift up 3/8 of a inch in the winter. Also make sure your attic ventilation is up to code. And correctly done.