On zoning lots above 20,000 square feet in lot area, up to 150,000 square feet of floor area within a public school, constructed in whole or in part pursuant to agreement with the New York City School Construction Authority and subject to the jurisdiction of the New York City Department of Education, shall be exempt from the definition of floor area for the purposes of calculating the permitted floor area ratio for community facility uses and the maximum floor area ratio of the zoning lot.