I’ve put a second story over my garage, and I need to insulate the underside of the upper floor, which is the same as the ceiling of the garage.  The joists are 2 x 12’s and the batts are 8″ thick.  I need to have them up against the floor.  I was just going to use twine in a zig-zag pattern to hold them up, but thought I’d ask if anyone has any other ideas.