In the Special Hudson Square District, the height and setback regulations of the underlying districts shall not apply. In lieu thereof, the provisions of this Section shall apply to all buildings.

1. Permitted obstructions
   
   The provisions of Section 33-42 shall apply to all buildings. n addition, dormers may penetrate a maximum base height provided that such dormers comply with the provisions of paragraph (c) of Section 23-632 (Permitted obstructions in certain districts).
2. Height and setback
   1. Street wall location
      
      On wide streets, and on narrow streets within 50 feet of their intersection with a wide street, the street wall shall be located on the street line and extend along the entire street frontage of the zoning lot up to the minimum base height or the height of the building, whichever is less. On narrow streets beyond 50 feet of their intersection with a wide street, the street wall shall be located on the street line. For the purposes of this paragraph (b), portions of street walls located up to 18 inches from a street line shall be considered to be located on the street line where a vertical element of such street wall is located on the street line and rises without setback from ground level to the top of the second story at intervals of at least once every 15 feet in plan and, above the level of the second story, where a vertical element rises without setback to the applicable minimum base height at an interval of at least once every 30 feet in plan.
      
      On the ground floor, recesses shall be permitted where required to provide access to the building, provided such recesses do not exceed three feet in depth as measured from the street line.
      
      Above the level of the ground floor, recesses shall be permitted beyond 20 feet of an adjacent building and beyond 30 feet of the intersection of two street lines, as follows:
      1. Along wide streets
         
         Recesses shall be provided at the level of each story entirely above a height of 60 feet, up to the maximum base height of the building. Such recesses shall have a minimum depth of five feet and a width between 10 and 40 percent of the aggregate width of street wall of the building at the level of any story.
      2. Along narrow streets
         
         Above the level of the second story, recesses in street walls deeper than 18 inches shall be permitted. Such recesses may not exceed 30 percent of the aggregate width of street wall of the building at the level of any story.
   2. Base height
      1. Along wide streets
         
         On wide streets, and on narrow streets within 50 feet of their intersection with a wide street, the street wall of a building shall rise without setback to a minimum base height of 125 feet and a maximum base height of 155 feet.
      2. Along narrow streets
         
         On narrow streets, beyond 50 feet of their intersection with a wide street, the street wall of a building shall rise without setback to a minimum base height of 60 feet, or the height of the building, whichever is less, up to a maximum base height of 135 feet.  However, for buildings on zoning lots meeting the criteria set forth in paragraph (a) of Section 23-664 (Modified height and setback regulations for certain Inclusionary Housing buildings or affordable independent residences for seniors), the maximum base height may be increased to 155 feet.
         
         As an alternative, the minimum and maximum base heights applicable to a wide street may apply along a narrow street to a distance of 100 feet from its intersection with a wide street.
   3. Required setbacks and maximum building heights
      1. Along wide streets
         
         For buildings, or portions thereof, located on wide streets, and on narrow streets within 100 feet from their intersection with a wide street, the portion of such building above the maximum base height set forth in paragraph (b)(2)(i) of this Section shall be set back from the street wall of the building at least 10 feet along a wide street and at least 15 feet along a narrow street, except such dimensions may include the depth of any permitted recesses in the street wall. The maximum height of such buildings shall be 290 feet. In addition, the gross area of each of either the highest two or three stories of such building located entirely above a height of 230 feet, shall not exceed 80 percent of the gross area of the story directly below such highest two or three stories.
      2. Along narrow streets
         
         For buildings, or portions thereof, located on narrow streets beyond 100 feet from their intersection with a wide street, the portion of such building above the maximum base height set forth in paragraph (b)(2)(i) of this Section shall be set back from the street wall of the building at least 15 feet, except such dimensions may include the depth of any permitted recesses in the street wall.
         
         The maximum height of a building and the maximum number of stories shall be as set forth in Section 23-662 (Maximum height of buildings and setback regulations) for an R10A District on a narrow street. However, for buildings meeting the criteria set forth in paragraph (a) of Section 23-664 (Modified height and setback regulations for certain Inclusionary Housing buildings or affordable independent residences for seniors), such maximum heights and number of stories may be increased, provided that the maximum number of stories does not exceed 23, the maximum height of a building with a non-qualifying ground floor does not exceed a height of 230 feet and the maximum height of a building with a qualifying ground floor does not exceed a height of 235 feet.
   4. Maximum length of street wall
      
      The maximum length of any street wall located entirely above a height of 150 feet shall not exceed 150 feet. Such length shall be measured in plan view by inscribing within a rectangle the outermost walls at the level of each story entirely above a level of 150 feet. As an alternative, for street walls facing wide streets that provide vertical articulation, such maximum length may be increased to 175 feet, provided that between 30 and 40 percent of the width of the street wall is recessed at least five feet from all adjacent street walls above a height of 150 feet.
   5. Vertical enlargements
      1. Existing buildings may be vertically enlarged by up to one story or 15 feet without regard to the street wall location requirements of paragraphs (b)(1) and (b)(2) of this Section.
      2. Existing buildings with street walls that rise without setback to a height of at least 80 feet may be vertically enlarged in excess of one story or 15 feet without regard to the street wall location requirements of paragraphs (b)(1) and (b)(2) of this Section, provided such enlarged portion is located at least 10 feet from a wide street and at least 15 feet from a narrow street.