Abstract: A concrete floor system includes the use of sheet metal pan or decking and sheet metal z-shaped closures sitting upon low profile open web steel joist providing a non-structural or structural concrete brake above the walls forming vibration damping and sound & fire barriers. The z-shaped closures have apertures formed through them which correspond to the end profiles of the joist shoes of the joists, and are fitted onto the joists before or after the joists are in place. The need for sound and vibration damping rock wool, foams and other similar material below the floor and between walls is eliminated.