In C6-4 Districts within the Park Avenue Hub Subdistrict, as shown on Map 1 in Appendix A of this Chapter, the following provisions shall apply. 

1. Street wall location
   
   The applicable provisions of Section 35-631 shall be modified as follows:
   1. Along 125th Street
      
      The street wall provisions of paragraph (a) of Section 35-631 shall apply. The minimum base height shall be 60 feet, or the height of the building, whichever is less, except that for buildings or portions thereof within 50 feet of Park Avenue, the minimum base height shall be 40 feet, or the height of the building, whichever is less. The street wall location provisions of this paragraph shall be modified to allow a sidewalk widening pursuant to the provisions of paragraph (a)(2) of this Section; and
   2. Along Park Avenue and narrow streets
      
      The street wall provisions of paragraph (b) of Section 35-631 shall apply, except that the minimum base height shall be 40 feet, or the height of the building, whichever is less.
      
      In addition, for zoning lots with frontage along Park Avenue between 124th Street and 125th Street, any development or horizontal enlargement shall provide a sidewalk widening along the street line of Park Avenue. Such sidewalk widening shall have a depth of 10 feet, be improved to Department of Transportation standards for sidewalks, and be at the same level as the adjoining public sidewalk. 
2. Basic maximum building height and setback regulations
   
   The maximum height of buildings or other structures shall be as set forth in the applicable provisions of Section 35-632, except that the minimum base height shall be as set forth in paragraph (a) of this Section, and the maximum base height for buildings or other structures along the street line of 125th Street and within 50 feet of such street line shall be 85 feet.
3. Optional height and setback regulations 
   
   As an alternative to the provisions of paragraph (b) of this Section, the provisions of this paragraph (c) may be applied to zoning lots providing qualifying affordable housing or qualifying senior housing, or zoning lots where 50 percent or more of the floor area is allocated to non-residential uses.
   1. Setbacks
      
      Above the applicable maximum base height established pursuant to paragraph (b) of this Section, any portion of a building or buildings on the zoning lot shall be considered a “tower.”
   2. Lot coverage requirements for towers
      
      The maximum lot coverage of a tower shall be as set forth in Section 23-435 (Tower regulations).
   3. Maximum building height
      
      No height limit shall apply to towers.