General requirements. For every building, structure or part thereof having over 3,000 square feet of gross floor area, erected and occupied for retail trade establishments, motels, places of public and quasi-public assembly and other similar uses involved in the receipt and distribution of materials or merchandise by vehicles, there shall be provided and permanently maintained adequate space for off-street 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 10,000 square feet of gross floor area.