1. Except as provided in paragraph (b) of this Section, the front building wall for all developments on zoning lots having frontage on Fifth Avenue or Park Avenue, and within 50 feet of their intersection with the street lines of Fifth Avenue or Park Avenue, the street wall location provisions of paragraph (a) of Section 35-631 (Street wall location) shall apply, except that the street wall shall extend without any articulation up to a height of 125 feet above curb level or the full height of the building, whichever is less. Above the height of 150 feet above curb level, the provisions of Section 23-433 (Standard setback regulations) shall apply. The mandatory front building wall requirements are optional for the next 20 feet along the street line of a narrow street or for the next 75 feet along the street line of a wide street. However, where the front wall of a building with a height less than 125 feet above curb level was constructed with a setback from the street lines, enlargement of such building may be permitted by vertical extension of its existing building wall.
2. For any zoning lot having frontage on Fifth Avenue or Duke Ellington Circle, and along East 109th Street and East 110th Street within 50 feet of their intersection with Fifth Avenue and Duke Ellington Circle, the street wall location provisions of paragraph (a) of Section 35-631 shall apply, except that the street wall shall extend without any articulation to a minimum height of 85 feet above curb level or the full height of the building, whichever is less. Above a height of 150 feet, the provisions of Section 23-433 shall apply. Such mandatory front building wall requirements are optional for the next 50 feet along the East 109th Street and East 110th Street street lines.
3. Front wall recesses are permitted within mandatory front building walls for architectural or decorative purposes pursuant to recess provisions of paragraph (a) of Section 35-631 except that the aggregate length at the level of any story does not exceed 50 percent of the length of the front wall where such recesses are permitted, the depth of such recesses shall not exceed six feet and no front wall recesses are permitted within 20 feet of the intersection of two street lines.

The underlying district height and setback regulations apply along street lines, or portions thereof, not subject to the front building wall requirement.