Open Plenum Ceiling

However calculating the tradeoffs between cost and performance can be tricky.

Open plenum ceiling. Space between the structural ceiling and the dropped ceiling or under a raised floor is typically considered plenum. Plenum spaces are the open spaces above the ceiling or below the floor that are used for air circulation. By the 1960s as building systems started becoming more complex and high performing with electronics and communications wiring wiggling throughout the work space suspended or dropped ceilings quickly became the more popular ceiling option.

Open plenum ceilings are common design practice these days seen more often than not in stores moving into newly built shopping environments. Technically any ductwork is considered a plenum space too. While suspended lay in ceilings have long been the norm in commercial design the open plenum ceiling has become trendy and economical particularly in office and retail environments.

For much of the 20th century of course open plenum ceilings were the choice of designers and building owners largely for reasons of initial cost. In short we take them for granted as an acceptable design solution. However some drop ceiling designs create a tight seal that does not allow for airflow and therefore may not be considered a plenum air handling space.

These spaces are important for air circulation in any building but they also bring some problems if you ever have a fire because of the high oxygen content and lack of fire barriers.