Is it acceptable for the blocking performance of your ceiling (CAC) to be less than the blocking performance of your wall (STC)?
Whether the noise comes through the wall or over the top of the wall through the ceilings, overall room performance is only as good as the weakest link. Therefore, the blocking capacity of the ceiling system (CAC), after accounting for all of the noise leaks, should equal the blocking capacity of the wall (STC). In reality, though, this cannot be the case. The best-performing ceilings alone cannot match the lowest performance achieved by common walls.
The ability of walls to block sound is commonly specified at levels of 10 to 20 dB higher than what common, modular, acoustic ceilings of any type can achieve. Beyond this, when designers incorporate typical mechanical, electrical and plumbing elements (e.g. lights, air supply diffusers, return grilles and sprinklers), they introduce penetrations into the ceiling which allow sound to leak through and reduce the overall effectiveness of the ceiling system to block sound. These ‘flanking paths,’ as they’re commonly referred to, can then reduce the sound blocking capabilities of ceiling systems by 10 dB more. Therefore, when you look at the difference between the ability of ceilings to block sound compared to walls, you’re looking at up to a 30 dB difference, making the amount of sound transmission between rooms approximately eight times louder. This reduction in sound blocking is enough to make speech from adjoining spaces intelligible – meaning privacy is lost – and aggravating.
Recognizing that ceiling panels should not be used as a primary source of noise blocking, it is important to consider the role of the room as a whole in achieving the blocking requirements for a space. For example, when privacy between rooms is required, the optimal way to meet isolation or blocking requirements is to use full-height walls or a lightweight plenum barrier – a barrier that rises from the top of the wall to the floor or roof deck above – to comply with minimum Sound Transmission Class (STC) ratings.
THE TRUTH: Ceilings are not effective at blocking noise. The overall blocking performance of your room design needs careful consideration and you should ensure performance meets industry leading guidelines, standards and rating systems levels for blocking performance. To achieve these values you should look to effective building components, such as walls and plenum barriers, where needed.