They go over existing walls, furred masonry, wood and steel framing, and masonry and concrete. However, WR panels should not be applied around tubs or showers or other areas subject to direct moisture. Like WR panels, however, Foil-Back panels should not be installed in direct moisture areas.
Ceilings are also perfect for places for drywalling.
U.S. Gypsum Company manufactures panels specifically for interior and exterior ceiling applications. Interior Ceiling Board can be attached to wood or steel framing.