A base plane is an imaginary horizontal plane that determines the elevation from which a building’s height is measured. There are multiple ways to calculate a base plane outlined in the NYC Zoning Resolution.
Base Plane Definition
The following is based on the New York City Zoning Resolution.
A Base Plane is an imaginary plane setting the elevation for measuring the height of a building or structure.
For buildings with street walls at least 15 feet wide and within 100 feet of the street the base plane is any level between the curb level and the street wall level. For buildings beyond 100 feet of the street the Base Plane is the average grade elevation at the building.
In the Food zone the Base Flood Elevation can be the base plane or the Flood-Resistant Construction Elevation may be.
Additional Base Plane Regulations
Within 100 feet of the street: The base plane cannot be higher then the average grade at the building wall (not counting a garage entrance). Unless the Base Plane is the Base Flood Elevation.
If the average grade elevation at the building is more than 2 feet bellow the curb level then the average grade will be the base plane. This does not apply if the Base Plane is the Base Flood Elevation. Certain zoning districts are exempt from this code. It will not apply in C1 or C2 Zoning within R2X, R3, R4, or R5 nor C3 or C4-1 unless they are also waterfront blocks. Additionally it will not apply to the following districts if developed before June 30th 1989 = R2X, R3, R4, and R5.
If there is a slope of at least 5% from the front wall to the rear wall, a sloping base plane may be used. In this case, the average grade cannot be below the rear wall line level.
If multiple base planes are used, the heights will only apply to the building per section for each applicable base plane.
for building partially within 100 feet and partially beyond 100 feet of a street line multiple base planes may be used. On corner or through lots with different elevatins multiple base planes may be used. Alternatively an adjusted base plane may be used calculated proportionally based on the lot coverage of each section of building.
Base Plane Calculation and Definition
As an architect I study Building and Zoning Codes closely, but these are complicated and quite involved issues. In this article we reviewed some of the basic concepts with regards to the Base Plane definition. This post does not assume to cover every possible issue or condition, but provide a general overview of the topic.
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This post was written by Jorge Fontan AIA a Registered Architect and owner of New York City architecture firm Fontan Architecture. Jorge Fontan has earned 3 degrees in the study of architecture including two degrees from the City University of New York and a Masters Degree in Advanced Architectural Design from Columbia University. Jorge has a background in construction and has been practicing architecture for 15 years where he has designed renovations and new developments of various building types.