The New York City Department of Buildings (DOB) recently clarified the meaning of, and approval process for, Ancillary Dwelling Units (ADUs) as part of the City of Yes Affordable Housing initiative. Here, we outline the key points owners need to know about ADUs.
What is an ADU?
For DOB purposes, an ADU is a small, independent residential dwelling unit located on the same lot as your home. The unit could be located within the existing home, or it could be a fully independent and detached structure. ADUs come in a variety of types, including basement apartments, attic conversions or in-law suites. ADUs are equipped with their own entrance, kitchen, bathroom, and living space.
To qualify as an ADU, the structure must be on same zoning lot as a single- or two-family residence that does not exceed eight hundred square feet of floor area.
What spaces are off-limits for an ADU?
In a high-risk flood zone, an ADU is not permitted below the flood-resistant construction elevation, or in a basement, cellar, or backyard. While the flood zone maps for ADUs are yet to be promulgated by the Department of Environmental Protection (DEP), they contemplate a “10-year rainfall flood risk area” based on 2050 sea level rise projections and “coastal flood risk area” where there is a 1% chance of flooding in any year based on 2080 sea level rise projection.
There are also no backyard ADUs permitted in R1-2A, R2A, or R3A Zoning Districts outside the “Greater Transit Zone,” or in Landmarks Preservation Commission-designated Historic Districts.
If an owner is seeking to convert or legalize an ADU that was non-complying as of December 5, 2024, the application will be denied if backyard ADUs are otherwise prohibited.
Who can live in an ADU?
The DOB isn’t concerned with who lives in the ADU, but rather who owns the land it’s on. The zoning lot on which the ADU is located must be the primary residence of an owner at initial occupancy.
How large can an ADU be?
ADUs as a permitted obstruction in a required rear yard are limited to one story, not to exceed 15 feet in height.
If a parking space is provided below a backyard ADU, the height of such building and associated ADU cannot exceed two stories or 25 feet above adjoining grade, including the apex of a pitched roof. ADUs created as part of a development or enlargement after December 5, 2024, do not require any additional parking spaces.
How far apart does an ADU need to be from other buildings?
For buildings with two or fewer dwelling units, the required minimum distance between such building and an ADU on the same zoning lot shall be 10 feet.
Backyard ADUs must be accessible directly from a side yard or open area along a side lot line with a minimum width of five feet.
If you’re looking to build, convert, or legalize an ADU, we can help you identify and resolve issues before they become obstacles. Contact us for details.
