For every building, structure or part thereof having over 4,000 square feet of gross floor area erected and occupied for commerce, 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 space 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 loading space. 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.