What construction type is required for the corridor ceiling to be used as a return air plenum?

The requirement for the corridor ceiling to be used as a return air plenum is that it must be of fire-resistance-rated construction. This is important because the air plenum space can carry significant air volumes, including potentially hazardous materials in the event of a fire. A fire-resistance-rated construction helps prevent the spread of fire and smoke throughout a building, ensuring that a fire in one area does not expose the plenum space and potentially spread to other areas.

In commercial and institutional buildings, where safety regulations are stringent, using fire-rated materials in plenum spaces is crucial. The materials used for the ceiling must meet specific fire safety standards, helping to maintain the integrity of the compartmentalization intended by the building design. This prevents air from other areas from entering the plenum and helps manage smoke and fire behavior, safeguarding occupants and property.

Thus, fire-resistance-rated construction is essential for any ceiling used as a return air plenum to ensure compliance with safety codes and to protect against fire hazards.