At the time of the erection of a structure containing more than
30 dwelling units or any main commercial building or structure, or
whenever any main commercial building or structure is enlarged in
capacity, off-street loading space with adequate means of ingress
and egress by standard-size, commercial vehicles shall be provided
at the rate of one loading stall for every 10,000 square feet of main
floor area. In no case shall more than two off-street loading stalls
be required. A required loading space may occupy the whole or a part
of a required rear yard.