Flat ceilings constructed of gypsum board that are screw-attached to suspension members that support a ceiling on one level extending from wall to wall, are generally exempt from acoustical seismic construction requirements such as: perimeter end wall clearance, perimeter hanger wires, horizontal restraint and vertical splay bracing. This is due to the diaphragm strength achieved by screw-attached gypsum board. Gypsum board ceilings that do not extend perimeter to perimeter, or have multiple levels, may require seismic bracing depending on the local code interpretation.