The Plenums tree object occupies the next highest position in the hierarchy below that of the Floor tree object. The plenums object is essentially a sub-floor occupying space above or below a room. Available plenum space is determined by two plenum default height settings in Defaults Manager or can be defined independently when using the room modeling tools. Plenums can contain multiple plenum room objects, each plenum room object is a ceiling plenum or an underfloor plenum independent of the room it is associated with. Plenums rooms are spaces like regular rooms, so they contain the same surface types including walls, ceilings, floors, partitions, and all associated sub-surface objects.