ancillary dwelling unit

General Definition An “ancillary dwelling unit” is an additional dwelling unit, permitted on the same zoning lot as a single- or two-family residence that does not exceed eight hundred square feet of floor area. Only one ancillary dwelling unit shall be permitted per every single- or two-family residence on a zoning lot. Ancillary dwelling units shall be subject to the following limitations: (a) in the high-risk flood zone, as defined in Section 64-11, no ancillary dwelling unit shall be permitted below the flood-resistant construction elevation; (b) in the areas included in maps promulgated by the Department of Environmental Protection (DEP) designating the “10-year rainfall flood risk area” based on 2050 sea level rise projections by the New York City Panel on Climate Change (NPCC), and the “coastal flood risk area” where there is a 1 percent chance of flooding in any year based on 2080 sea level rise projections by the NPCC, including as such maps and baseline reference dates are updated by subsequent rulemaking by DEP: (1) no ancillary dwelling units shall be permitted in a basement or cellar; and (2) no backyard ancillary dwelling units shall be permitted; (c) in R1-2A, R2A and R3A Districts, or portions thereof, located beyond the #Greater Transit Zone, no backyard ancillary dwelling units# shall be permitted; (d) in Historic Districts designated by the Landmarks Preservation Commission, no #backyard ancillary dwelling units# shall be permitted; (e) backyard ancillary dwelling units shall be accessible directly from a side yard or open area along a side lot line with a minimum width of five feet; and (f) at the time of initial occupancy for an ancillary dwelling unit, the zoning lot on which the ancillary dwelling unit is located must be the primary residence of an owner of such #zoning lot#. In areas where backyard ancillary dwelling units are prohibited, nothing herein shall permit the legalization of an ancillary dwelling unit in a building or other structure that prior to December 5, 2024, was non-complying as to its location within a required yard or open space.