ADU rules in New York, NY — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
New York City legalized ADUs on one- and two-family lots in December 2024 through Local Law 126 of 2024 (basement/cellar legalization pilot) and Local Law 127 of 2024 (new ADU standards), enacted alongside the City of Yes for Housing Opportunity zoning text amendment. ADUs are capped at 800 square feet of zoning floor area, limited to one ADU per lot, and require owner-occupancy on the same lot. Backyard ADUs are prohibited in FEMA Special Flood Hazard Areas, DEP 10-Year Rainfall Flood Risk Areas, historic districts, and certain low-density zones (R1-2A, R2A, R3A) outside the Greater Transit Zone.
Until 2024, NYC's Multiple Dwelling Law and Zoning Resolution effectively barred most ADUs in one- and two-family homes. The City of Yes for Housing Opportunity text amendment (adopted by the City Council on December 5, 2024) and companion Local Laws 126 and 127 of 2024 established the first comprehensive ADU framework in NYC. Local Law 127 sets zoning, construction, fire safety, and occupancy standards for new ADUs created in attics, basements, cellars, attached additions, garage conversions, or detached backyard structures. Local Law 126 creates a pilot legalization program for pre-existing basement and cellar apartments built before April 20, 2024 in eligible community districts, allowing tenants to remain while owners bring units into compliance over a 10-year period. Subgrade ADUs (basement/cellar) are not permitted in FEMA Special Flood Hazard Areas, the Coastal Flood Risk Area, or DEP's 10-Year Rainfall Flood Risk Area. Backyard ADUs are excluded from historic districts, R1-2A, R2A, and R3A zones outside the Greater Transit Zone, and the Special Bay Ridge District. ADU rules are administered by the Department of Buildings (DOB) and Department of City Planning (DCP). New York State's Plus One ADU grant program offers up to $125,000 per homeowner to support construction.
Unpermitted ADUs are subject to DOB violations, stop-work orders, and civil penalties. Illegal basement and cellar conversions outside the Local Law 126 pilot remain unlawful and may result in vacate orders. Occupied basement/cellar units without proper egress, ceiling height, and light/ventilation are dangerous and can be ordered vacated by DOB or HPD.
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