[cu.ft.] Volume inside the building envelope of the conditioned spaces. This metric can be calculated as the volume of the building if every space is conditioned or on a floor-by-floor basis. For spaces with vertical walls and horizontal ceilings and floors, this is calculated as the Gross Conditioned Floor Area times the height from the top surface of the finished floor to the top surface of the finished floor separating levels of the building or to the inside surface of the roof for the top floor. The volume of spaces that have nonvertical walls or nonhorizontal ceilings of floors should be calculated separately to properly account for the non-rectangular geometry. This metric does include the volume of floor or ceiling return air plenums.