No-Sag Ceiling Anew type of 1/2-inch drywall promises to eliminate ceiling sags on 24-inch on-center framing. Domtar's CD Ceiling Board has a three-layer, "controlled density" gypsum core. The outermost layers on each side are denser than a conventional gypsum board core. The inner layer is lighter. The overall reported effect of this "controlled density" core is a more rigid board that is only slightly heavier than standard drywall and snaps cleaner when cut. With the increased density, the new board may have better sound ratings, but at press time the product was still being tested. There is no increase in the fire rating of the CD Board, though Domtar reports that a 1/2-inch fire-rated product will be available soon. CD