(1) Except as provided in subsection (3), every occupancy-unit and every portion of an occupancy-unit occupied by a separate tenant shall be separated by means of an occupancy-separation structure or a tenancy-separation structure, as the case may be, complying with section 13, from any adjoining occupancy-unit or portion thereof, as the case may be.

(2) Except as provided in subsection (3), where there are several occupancy-units in a building, all of which do not have the same occupancy, each such occupancy-unit shall comply with the requirements of this Chapter applicable to it.

(3) The provision of occupancy-separation structures between different occupancy-units comprised in one building, as set out in subsection (1), may be omitted between such occupancy-units as are in one tenancy, if all such occupancy-units comply with the requirements of this Chapter which are applicable to that occupancy-unit included in them which requires the most stringent precautions.