To analyze a portion of a mass that occurs below the lowest mass floor, create a level and mass floor at the bottom-most boundary of the mass. Otherwise, Revit does not include that portion in the surface area or volume calculations for any mass floors. As an alternative, you can examine the Gross Surface Area and Gross Volume parameters for the mass.
Note: The Gross Surface Area includes the bottom surface of a mass. However, the combined exterior surface areas of mass floors include the sides and top of the mass, but not its bottom surface.
