No yard or lot existing at the time of passage of the Zoning Ordinance shall be reduced in dimension or area below the minimum required by this Zoning Ordinance. No part of a yard or other open space, or off-street parking or loading space, provided about any building, structure or use for the purpose of complying with the provisions of this Zoning Ordinance, shall be included as part of a yard, open space or off-street parking or loading space for another building, structure or use. Off-street parking and loading areas may occupy part of any required yard, subject to the provisions of Section 194.01.