16. a. Notwithstanding any other provision of law to the contrary, within a dwelling to which this section is applicable the use of dwelling units as a hotel for other than permanent residence purposes, as defined in paragraph a of subdivision eight of section four of this chapter, that would otherwise be prohibited shall be permitted to continue for a period of two years after the effective date of this subdivision provided that:

1. (1) such dwelling units were used for other than permanent residence purposes on January first, two thousand nine and on the effective date of this subdivision and fifty-one percent or more of the total number of dwelling units in such dwelling were used for other than permanent residence purposes on such dates;
2. (2) such dwelling was occupied as a hotel for other than permanent residence purposes on December fifteenth, nineteen hundred sixty-one;
3. (3) such dwelling is of fireproof construction and was of fireproof construction on January first, two thousand nine;
4. (4) such dwelling units used for other than permanent residence purposes have at least two lawful means of egress, including exit stairs, fire towers or exterior stairs but excluding fire escapes and had such lawful means of egress on January first, two thousand nine;
5. (5) such dwelling has operational exit signs and a fire alarm system complying with the provisions for existing transient occupancies in accordance with local law and had such exit signs and fire alarm system on January first, two thousand nine; and
6. (6) such dwelling units used for other than permanent residence purposes are registered with the department within one hundred eighty days after the effective date of this subdivision in a form and manner to be provided by such department, including a requirement that the applicant submit certification of compliance with subparagraphs three, four and five of this paragraph, signed and sealed by a registered architect or licensed professional engineer in good standing under the education law. The department may assess fees to cover all costs associated with such registration. The department may refuse to register dwelling units or may revoke such registration if it determines such dwelling units or dwelling do not comply with the conditions for registration set forth in subparagraphs one through five of this paragraph. b. The owner shall obtain a certificate of occupancy for the use of registered dwelling units for other than permanent residence purposes within two years after the effective date of this subdivision. Upon application prior to the expiration of such two year period, the department may, for good cause, extend such time for up to one additional year but no such extension shall be granted unless the department finds that:
7. (1) the owner has obtained the necessary permit or permits for all work necessary to bring such dwelling into compliance with the requirements of this chapter and all local housing, building and fire codes for the use of dwelling units for other than permanent residence purposes;
8. (2) all construction authorized by such permit or permits has been substantially completed; and
9. (3) there are no considerations of public safety, health and welfare that have become apparent since the issuance of the above described permit or permits that indicate an overriding benefit to the public in enforcing the requirement that the applicant obtain a certificate of occupancy for the use of registered dwelling units for other than permanent residence purposes within two years after the effective date of this subdivision. c. Upon application prior to the expiration of the time for obtaining a certificate of occupancy, as extended by the department pursuant to paragraph b of this subdivision, the board of standards and appeals may grant a further extension of time to obtain a certificate of occupancy in a case where there are circumstances beyond the applicant's control or hardship in the way of obtaining such certificate within the time allowed by the department but no more than one such extension of fifteen months shall be granted for a building and no such extension shall be granted unless the board finds that there are no outstanding building or fire code violations of record at the property. d. The department shall issue such certificate of occupancy upon proof that said dwelling conforms in all respects to the requirements of this chapter and all local housing, building and fire codes for the use of dwelling units for other than permanent residence purposes. If no such certificate of occupancy is issued within two years after the effective date of this subdivision or, if applicable, within the time as extended by the department or as further extended by the board of standards and appeals, all use of dwelling units for other than permanent residence purposes shall thereafter cease. e. If after a certificate of occupancy is issued pursuant to paragraph d of this subdivision, the use of such dwelling units for other than permanent residence purposes is discontinued, nothing in this subdivision shall be construed to limit the application of the local zoning resolution with respect to such discontinuance.