In all districts, in connection with every building or part thereof hereafter erected, having a gross floor area of 2,500 square feet or more, which is to be occupied by uses requiring the receipt or distribution by vehicles of materials or merchandise there shall be provided and maintained on the same premises with such building at least one off-street loading space accessible from an alley, easement of access or, when there is no such alley or easement of access, from a street, plus one additional such loading space for each 10,000 square feet or major fractions thereof or gross floor area so used in excess of 15,000 square feet. Such space may occupy all, or any part of a required rear yard, or upon authorization of the Board, part of any other yard of court space on the same premises.