The optional predominantly built-up area provisions of Section 23-71, inclusive, may be applied to zoning lots:

1. that have a lot area of not more than 1.5 acres; 
2. located on a block:
   1. that is entirely within R4 or R5 Districts without a letter or number suffix, including a Commercial District mapped within such Residence Districts; 
   2. that has a maximum area of four acres; 
   3. where the buildings on zoning lots comprise 50 percent or more of the area of the block; and
3. where, as of October 21, 1987, not more than 75 percent of the aggregate length of the block frontages facing each other around the zoning lot, on both sides of the street, are allocated to single- or two-family detached or semi-detached residences. 

All buildings used in calculations shall have certificates of occupancy or other evidence acceptable to the Commissioner of Buildings issued prior to the date of application for a building permit.