On a multi-tenancy floor, the gross area minus core space. Core space includes the square footage used for public corridors, stairwells, washrooms, elevators, electrical and janitorial closets, and fan rooms. On a single-tenant floor, the usable area is the gross square footage excluding building lobby and all penetrating shafts (i.e. ducts, stairwells and elevators).

That area of a space that may actually be occupied by a user. [Equation: Usable area = Rentable area - Common area

Area in a dome loft with six foot headroom or more