To indicate that an element should be used to define the boundaries of a room for room area and volume computations, you must specify that the element is room-bounding.
By default, the following elements are room-bounding:
You can indicate whether many elements are room-bounding by changing element properties. For example, you may want to define toilet partitions as non-bounding because they are not usually included in room computations. When you specify that an element is non-bounding, the element is not used when Revit computes the area or volume of the room or any adjacent rooms that share the non-bounding element.
You can also use many elements in linked IFC files as room boundaries.