What is the plenum in building construction?

• A. The space between the finished ceiling and the underside of the structure that may contain ductwork, plumbing, and wiring.
• B. A type of sound-absorbing panel used on walls.
• C. A partition that extends full height to separate rooms.
• D. A decorative vent cover.

Answer: (A)

The plenum is the space between the finished ceiling and the structure above, where mechanical services like ductwork, plumbing, and wiring run. This air-handling or service space is used to route systems and, in HVAC, can act as a return air chamber. It’s not a sound-absorbing panel, a full-height partition, or a decorative vent cover. In other words, it’s the hidden corridor above the ceiling that houses building services.