As used in this article, the following terms shall have the meanings indicated:
BASEMENTA story partly underground but having at least 1/2 its height, measured from finished floor to finished ceiling, above the curb level at the center of the street front.
CELLARA story having more than 1/2 its height, measured from finished floor to finished ceiling, below the curb level at the center of the street front.
GROUND FLOOR AREAThe area within the exterior of the walls of the building at grade level, excluding attached garages, unenclosed porches or breezeways but including incorporated garages with livable floor area above them.
LIVABLE FLOOR AREAThe aggregate area of all floors included within the outer walls of a building, excluding basements, cellars, rooms for heating equipment, garages, unenclosed porches, unfinished attics and storerooms and other unheated areas and including only such floor area under a sloping ceiling for which the headroom is not less than five feet, and then only if at least 60% of such floor has a ceiling height of not less than seven feet six inches and if any such floor that is situated above another story has access to the floor below by a permanent built-in stairway. However, 1/2 of the floor area of completely finished and heated rooms in a basement may be included in the aggregate area.