Ceiling Attenuation Class (CAC) ceiling systems display the resistance to sound passing up and over a wall. The acoustic rating given for the ceiling system indicates the sound reduction from one room to the next via the two ceilings and the above-ceiling plenum.

Rather than introduce another term to building designers such as CAC, the more familiar terms Rw and Rw + Ctr are used.

When sound isolation is important, the Rw of the CAC ceiling system should equal the Rw rating of the dividing wall plus 5.

[Refer to secion 4.1.1 construction details for wall to ceiling finishing details].