UPDATE: Applications for new ADUs are not currently being accepted until DOB and DEP rules are promulgated. (Last Revised: 08/12/25)
In December 2024, New York City enacted Local Laws 126 and 127 alongside the City of Yes for Housing Opportunity zoning text amendment to support the safe creation and use of Ancillary Dwelling Units (ADUs) in one- and two-family homes. These initiatives expand housing options by allowing homeowners to add new ADUs in attics, basements, cellars, free-standing buildings, or buildings attached to the primary residence.
Local Law 126 enables the legalization of some pre-existing basement and cellar apartments in specific NYC areas that have been occupied unlawfully. It establishes a procedure to gradually bring these units into compliance with Local Law 127 over a ten-year period. Local Law 127 sets comprehensive requirements for zoning, construction, fire safety, and occupancy, creating a clear framework for adding housing while protecting health and safety.
General Requirements for All NYC ADUs
- One ADU per Lot: Only one ADU is allowed per one- or two-family residence.
- Owner Occupancy: The homeowner must live on the zoning lot with the ADU.
- Maximum Size: The ADU cannot exceed 800 sq. ft. of zoning floor area.
- Separate Entrance: Each ADU must have its own private entrance.
- Multiple Dwelling Law Trigger: A two-family building adding an attic, basement, cellar, or attached ADU is treated as a three-family building under the MDL, unless separated by a fire wall.
- Legalization Compliance: Two-family buildings with pre-existing basement or cellar units undergoing legalization must follow Building Code Appendix U and additional fire and safety regulations.
Exceptions & Restrictions
Not all lots are eligible for ADU creation. Restrictions include:
- Backyard ADUs: Prohibited in Historic Districts; R1-2A, R2A, and R3A districts outside the Greater Transit Zone; and the Special Bay Ridge District (west of Ridge Blvd or south of Marine Ave). Converting an existing garage is not considered a backyard ADU and may be allowed.
- Subgrade ADUs: Basements or cellars in high-risk flood zones (FEMA Special Flood Hazard Areas, Coastal Flood Risk Areas, DEP 10-Year Rainfall Flood Risk Areas) are prohibited.
- Legalization Program Areas (LL126): Subgrade dwelling legalization applies only to pre-existing units in certain districts:
- Bronx: Community Districts 9, 10, 11, 12
- Brooklyn: Community Districts 4, 10, 11, 17
- Manhattan: Community Districts 2, 3, 9, 10, 11, 12
- Queens: Community District 2
ADU Legalization Under Local Law 126
Pre-existing basement or cellar units occupied prior to April 20, 2024, may be converted into legal habitable dwellings under Local Law 126 if they are in the program area and outside flood risk zones.
- Subgrade ADUs can continue to be occupied while meeting each milestone outlined in the Authorization for Temporary Residence (ATR).
- Units must comply with the LL126 compliance timeline and achieve certification at each milestone.
- Legalization ensures these units gradually meet all requirements under Local Law 127, protecting safety and health while creating legal housing opportunities.
Types of NYC ADUs
Detached Backyard Units
Free-standing units offering privacy and independent living.
Attached "In-Law" Suites
Units attached to the primary home with separate entrances for independence.
Basement or Attic Conversions
Transforming existing subgrade or attic spaces into habitable units under strict fire and egress rules.
Garage Conversions
Converting garages into legal ADUs, often exempt from backyard ADU zoning restrictions.
Financial Strategy: Plus One ADU Grant Program
New York State HCR offers the Plus One ADU Program, providing eligible homeowners up to $125,000 for design, permitting, and construction. Integrating this funding into your pre-construction plan maximizes feasibility and reduces upfront costs.
FAQs: NYC ADUs & City of Yes
When will new ADU applications open?
Applications are pending final DOB and DEP rules. Start planning and design now to be ready.
Who is eligible to build an ADU?
Homeowners of one- or two-family lots who reside on the property are eligible, subject to zoning, size, and flood restrictions.
Can I legalize my existing basement or cellar unit?
Yes, if the unit existed prior to April 20, 2024, is in the LL126 program area, and complies with ATR milestones and safety regulations.
Are backyard ADUs allowed everywhere?
No, they are prohibited in Historic Districts, certain low-density zones, and the Special Bay Ridge District. Garage conversions may still be allowed.
What is the maximum size for an ADU?
ADUs cannot exceed 800 sq. ft. of zoning floor area.
From Complexity to Certainty
NYC’s new ADU laws create one of the most exciting opportunities for homeowners in decades. Success requires expert navigation of zoning, construction, fire, and occupancy rules.
Buildley’s integrated design-build model provides a single point of accountability, turning complex regulations into a seamless, legally compliant, and valuable ADU project.
Schedule an ADU Feasibility Consultation