The cheap garage wall covering thread rocked my memory. I have a 2 1/2 car attached garage that has open trusses supporting the roof. When I temporarily heat it for a car repair, etc, most of the heat goes out the roof. Any ideas for an inexpensive material to attach to the underside of the trusses? I'd like something better than plastic sheeting, but less substantial than drywall. I thought of making a grid of 1x2s and dropping in 4x8 sheets of foam board, similar to a suspended ceiling. The wall common with the house has 5/8" drywall for a fire stop, but I'm not sure what code requires for a garage ceiling.