a. In every multiple dwelling, where all apartments, suites of rooms and single room units, at any time after July fourteenth, nineteen hundred sixty-seven:
(1) Became untenanted for a period of sixty days or more, or
(2) Were, or shall become, untenanted by reason of having been vacated by the department under the provisions of the administrative code or any provision of the multiple dwelling law on the ground that such dwelling was or is deemed unfit for human habitation or dangerous to life and health, it shall be unlawful for the owner of such dwelling to cause or permit same to be used in whole or in part for living purposes (other than by a janitor, superintendent or resident caretaker) until such dwelling is made to comply with the applicable requirements of the administrative code and the multiple dwelling law affecting the kind and class of such structure. For the purpose of determining whether any such dwelling is untenanted, occupancy of same by a janitor, superintendent or resident caretaker shall not be counted. It shall be unlawful for the owner of any such dwelling to cause or permit same to be used in whole or in part for living purposes (other than by a janitor, superintendent or resident caretaker) until (1) an application and plan for the work required by this article have been filed with and approved by the department, (2) such work has been completed by the owner and approved by the department, and (3) a new certificate of occupancy has been obtained.
b. The provisions of this article shall not apply to:
(1) any multiple dwelling which is vacant or partly vacant because of a current alteration being performed under application and plan approved by the department for the elimination of interior rooms or the installation of sanitary facilities as required by the provisions of the administrative code or the multiple dwelling law, or
(2) any multiple dwelling which is vacant or partly vacant by reason of being used as a summer resort dwelling as defined in paragraph fortysix of subdivision a of section 27-2004 of article one of subchapter one of this chapter, or
(3) any old law or new law tenement for which no certificate of occupancy has been issued, two or more apartments are being combined to create larger residential units, the total legal number of families within the building is being decreased and the bulk of the building is not being increased.