Our ceiling is 24 inches on center. I know we are supposed to hang drywall perpendicular to the ceiling but is it OK to hand the 12 ft. wide drywall (5/8 in. thick) without any more bracing between the wood. The old ceiling in the kitchen ripples (sags) from ceiling joist to joist (Ihope this is the right word for the horizontal wood in the ceiling). I don't want this to happen on the new bedroom drywall job. Any suggestions on the layout. We are planning on long twelve foot sheets running side by side.