New York County, NY Accessory Structures: ADU Rules (2026)

New York County (Manhattan) does not allow traditional accessory dwelling units the way California or Washington cities do. The NYC Zoning Resolution defines dwelling units by district and does not permit a second independent unit to be carved out of most Manhattan homes without a full zoning-compliant conversion. Basement and cellar apartments have long been restricted under the NYC Housing Maintenance Code and Multiple Dwelling Law due to egress, ceiling height, light, and ventilation requirements. NYC launched a limited basement legalization pilot in select outer-borough areas, but Manhattan is largely excluded. New York State 2024 housing legislation did not preempt NYC zoning for ADUs. Manhattan property owners seeking to add a unit must generally go through a full DOB Alt-1 alteration, potentially a zoning variance from the Board of Standards and Appeals, and comply with Multiple Dwelling Law classification. Illegal conversions are aggressively enforced with vacate orders and fines. Contact DOB and a zoning attorney before attempting any unit addition.