The requirements of Section 15-211 or 15-212 regarding the amount or configuration of floor area to be preserved for permitted commercial or permitted manufacturing uses may be modified by the Chairperson of the City Planning Commission provided that:

(a)        such floor area has a residential certificate of occupancy, or consists of registered Interim Multiple Dwellings, or is found covered by the New York City Loft Board pursuant to Article 7C of the New York State Multiple Dwelling Law, or was occupied as dwelling units as of September 1, 1980, and a complete application for determination of occupancy has been filed with the Department of City Planning by the owner of the building or the occupant of a dwelling unit in the building not later than June 21, 1983.  For the purposes of Article 7C of the New York State Multiple Dwelling Law, such a determination of residential occupancy shall be deemed to permit residential use as-of-right for such floor area; and

(b)        as a result of such residential occupancy, the remaining amount of floor area in the building is less than the amount required to be preserved for permitted commercial or manufacturing uses pursuant to Section 15-211 or 15-212, or consists of portions of floors.

Such modification of the preservation requirement shall be the minimum necessary in order to permit the legalization of existing dwelling units for which a determination of occupancy has been made.

Notwithstanding the above, the Chairperson of the City Planning Commission shall not issue a certification pursuant to Section 15-21 until an application for such certification and modification is submitted by the owner of the building.