For all residential buildings, or portions thereof, including those existing on December 15, 1961, the factor to determine the maximum number of dwelling units shall be 680.

Where a joint living-work quarters for artists has utilized the provisions of Section 15-024 (Special bulk regulations for certain pre-existing dwelling units, joint living-work quarters for artists and loft dwellings) as alternative density provisions, such provisions shall remain in effect for any subsequent conversion to dwelling units. However, in applying such provisions, the dwelling unit factor provisions of this Section shall apply in lieu of Section 15-111 (Number of permitted dwelling units).