1. If any separate multiple dwelling is erected after April eighteenth, nineteen hundred twenty-nine, upon the rear of a lot which has another multiple dwelling on the front or upon the front of a lot which has another multiple dwelling on the rear, access shall be provided to the rear dwelling from a street by means of an unobstructed court at least twenty feet in width.
2. Except as otherwise provided for motor vehicle storage space in section sixty and for dwellings erected, enlarged, converted or altered pursuant to plans filed prior to December fifteenth, nineteen hundred sixty-one in accordance with the provisions of subdivision one of section twenty-six, if any building or dwelling is placed on the rear of the same lot with a multiple dwelling or a multiple dwelling is placed anywhere on the same lot with another building, there shall be left between the two buildings an open space unoccupied from the ground up and at least forty feet in depth, measured in the direction from one building to the other for the first one hundred twenty-five feet above the curb level, and eighty feet above that point. The provisions of this subdivision requiring an open space eighty feet in depth between portions of buildings in excess of one hundred twenty-five feet above the curb level shall not be applied when both such portions are towers.
3. If on the rear of a lot any such building or any portion thereof is used for business purposes, a separate passageway at least three feet six inches wide and seven feet high shall be provided leading from every such open space adjacent to such building to a street. No such passageway shall connect with, go through or form a part of any entrance hall or other public hall of a multiple dwelling upon the front of the lot.