For the purposes of calculating the number of parking spaces or loading spaces required, the term “floor area” shall mean the floor area of space used for service to the public as customers, patrons, clients, or patients, or occupied by tenants of the offices in the case of an office building. The term shall include floor area occupied by fixtures and equipment used for display or sale of mer-chandise; but shall not include floor space used for non-public purposes such as storage, incidental repair, processing or packaging of merchandise, show windows or offices incidental to the management or maintenance of stores or buildings. Floor space used principally for toilet or rest rooms, fitting or dressing or alteration rooms, for utilities and for parking or loading spaces within the building shall also be excluded from floor area. (Prior gen. code § 8-63.16)