"Footprint" means the floor area of a structure or structures, as used in calculating lot coverage. Footprint shall be the horizontal projection of the plan areas included within the surrounding exterior walls of the structure. The plan area of a structure, or portion thereof, not provided with surrounding exterior walls shall be the usable area under the horizontal projection of the roof or floor above. (Ord. 01-412 §1 (Ehx. 1 (part)), 2001: Ord. 202 §2.12, 1987)