For every building, structure or part thereof having over 5,000 square feet of gross building area erected and occupied for commerce, hospital, laundry, dry cleaning, places of public and quasi-public assembly, industry, and other similar uses involved in the receipt and distribution by vehicles of materials or merchandise, there shall be provided and permanently maintained adequate spaces for standing, loading, and unloading services in order to avoid undue interference with the public use of streets or alleys. Every building, structure or addition thereto having a use which complies with the above definition shall be provided with at least one truck standing, loading, and unloading space to the rear or side of the premises not less than 12 feet in width, 35 feet in length, and 14 feet in height. One additional truck space of these dimensions shall be provided for every additional 20,000 square feet, or fraction thereof, of gross area in the building. No loading or unloading shall be conducted in the front of any store.