“Net floor area” means the sum of the total horizontal areas of the several floors of all buildings on a lot, measured from the interior faces of exterior walls and from the centerline of walls separating two or more buildings. The term net floor area shall include outdoor display areas for the sale, rental and display of recreational vehicles, boats and boating equipment, trailers, horticultural items, farm or garden equipment and other similar products, but shall exclude areas designed for permanent uses such as toilets, utility closets, malls enclosed or not, truck tunnels, enclosed parking areas, meters, rooftop mechanical structures, mechanical and equipment rooms, public and fire corridors, stairwells, elevators and escalators. (Ord. 871 §2 (part), 1989).