Prohibition of back-to-back buildings.

Notwithstanding anything contained in this Act, it shall not be lawful to erect any back-to-back buildings intended to be used as dwellings for the poorer classes, and any such building shall, for the purposes of this Act, be deemed to be unfit for human habitation: Provided that nothing in this section shall prevent the erection or use of a building containing several tenements in which tenements are placed back-to-back, if in the opinion of the Commissioner the several tenements are so constructed and arranged as to secure effective ventilation of all habitable rooms in every tenement.]