Definition: base plane (General Definition)
The "base plane" is a plane from which the height of a building or other structure is measured as specified in certain Sections. For buildings , portions of buildings with street walls at least 15 feet in width, or building segments within 100 feet of a street line , the level of the base plane is any level between curb level and street wall line level . Beyond 100 feet of a street line , the level of the base plane is the average elevation of the final grade adjoining the building or building segment , determined in the manner prescribed by the New York City Building Code for adjoining grade elevation. For the purposes of this definition, abutting buildings on a single zoning lot may be considered a single building . In addition, the following regulations shall apply: (a) Within 100 feet of a street line : (1) The level of the base plane for a building or building segment without a street wall shall be determined by the average elevation of the final grade adjoining such building or building segment . (2) Where a base plane other than curb level is established, the average elevation of the final grade adjoining the street wall of the building or building segment , excluding the entrance to a garage within the street wall , shall not be lower than the level of the base plane . (3) Where the average elevation of the final grade adjoining the street wall of the building , excluding the entrance to a garage within the street wall , is more than two feet below curb level , the level of the base plane shall be the elevation of such final grade. This paragraph shall not apply to buildings developed before June 30, 1989, in R2X, R3, R4 or R5 Districts. Furthermore, this paragraph shall not apply to buildings in C1 or C2 Districts mapped within R2X, R3, R4 or R5 Districts, or in C3 or C4-1 Districts, unless such buildings are located on waterfront blocks . (4) As an option, on sites which slope from the street wall line level to the rear wall line level by at least five percent to the horizontal, the level of the base plane may extend in a sloping plane from such street wall line level to such rear wall line level . When a sloping base plane is thus established, the average elevation of the final grade at the rear wall line shall not be lower than the rear wall line level . (b) For all buildings , where base planes of different elevations apply to different portions of a building , only that portion of the building to which such base plane applies may be used to determine such base plane . (c) For buildings located partially within and partially beyond 100 feet of a street line , or where corner lot or through lot regulations subject different portions of a building to base planes of different elevations, separate base planes may be determined for each such portion of the building or, as an option, the elevation of each such base plane may be multiplied by the percentage of the total lot coverage of the building to which such base plane applies. The sum of the products thus obtained may be the elevation of the adjusted base plane applicable to such building .