The underlying floor area regulations shall be modified as follows:

1. the maximum floor area ratio permitted for commercial uses shall be 8.0 in C6-3 Districts and 12.0 in C6-4 Districts;
2. in all Districts, the maximum floor area ratio permitted for residential uses shall be as set forth pursuant to the underlying district regulations, except that sky exposure plane buildings shall not be permitted;
3. the maximum floor area ratios may only be exceeded where:
   1. a floor area bonus for mass transit station improvements is granted by the City Planning Commission pursuant to the provisions of Section 66-51 (Additional Floor Area for Mass Transit Station Improvements); or
   2. a floor area bonus for a public plaza is granted by the City Planning Commission in accordance with the provisions of Section 115-52 (Authorization for a Public Plaza); and
4. for zoning lots with a lot area of at least 20,000 square feet, up to 150,000 square feet of floor space within a public school constructed in whole or in part pursuant to a written agreement with the New York City School Construction Authority and subject to the jurisdiction of the Department of Education shall be exempt from the definition of floor area.