NASCLA Accredited Commercial General ContractorFinishesHard
A contractor is installing a suspended acoustical ceiling in a large classroom. The specification requires the ceiling assembly to have a Ceiling Attenuation Class (CAC) of 35. What does the CAC rating primarily measure?
- AThe fire resistance of the ceiling tiles.
- BThe overall noise reduction within the room.
- CThe ability of the ceiling system to block sound transmission between adjacent rooms.
- DThe amount of sound absorbed by the ceiling panel.
Show answer & explanationAnswer & explanation
Correct answer: C. The ability of the ceiling system to block sound transmission between adjacent rooms.
Ceiling Attenuation Class (CAC) is a measure of a ceiling system's ability to block sound from traveling over the top of demising walls between adjacent, open-plan spaces. It's distinct from NRC, which measures sound absorption within a single room.
Why the other options are wrong
- A. Fire resistance is measured by hourly ratings (e.g., 1-hour fire rated), not CAC.
- B. This is a general acoustic performance goal, but CAC specifically addresses sound blocking between spaces.
- D. This describes the Noise Reduction Coefficient (NRC), not CAC.
Ceiling Attenuation Class (CAC)
A single-number rating indicating the effectiveness of a suspended ceiling system in blocking sound transmission between adjacent rooms through the plenum.
- Measures sound blocking, not sound absorption.
- Higher CAC values (e.g., 35+) indicate better sound privacy between rooms.
- Distinguished from NRC (Noise Reduction Coefficient).
Memory trick: CAC is the CEILING's sound BLOCKADE between rooms.