Building an ADU in New York City

What you can build

City of Yes for Housing Opportunity added ADUs to New York City's zoning for the first time. The Department of City Planning says it "allows ADUs in one and two-family homes in all low-density districts, with restrictions on certain types in certain areas to address concerns around flooding and neighborhood context." Local Law 127 of 2024 sets the construction, fire safety and occupancy rules, Local Law 126 of 2024 created a basement legalization pilot, and both took effect June 16, 2025.

The Zoning Resolution defines an "ancillary dwelling unit" as an additional dwelling unit 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 ADU is allowed per one- or two-family residence on a zoning lot. If two one-family homes share a zoning lot and each has its own tax lot, each can have one ADU.

DOB lists these ADU types:

• Above-grade ADU in a one-family home: in an attic, a new floor or a horizontal addition, with a 1-hour fire separation. Attic ADUs need sprinklers.
• Basement or cellar ADU: allowed in one- or two-family homes; cellar ceilings must be at least two feet above the grade plane.
• ADU attached to a two-family home and separated by a fire wall: a concrete or masonry fire wall from foundation to roof.
• Detached ADU: a new backyard cottage or a converted garage on the same lot as a one- or two-family home.
• Manufactured home: a home certified by New York State or HUD may be used, but DOB says its rule on them is still in development.

Every ADU needs a separate entrance, from outside or from a public corridor in the main home. ADUs do not need separate utility services, but they need their own controls, disconnects and shutoffs. [1][2][3][4][5][6]

Where ADUs are not allowed

ADUs are allowed only where zoning permits residences. The Zoning Resolution and DOB list these limits:

• Backyard ADUs (a building developed after December 5, 2024 whose only dwelling unit is the ADU) are not allowed in historic districts designated by the Landmarks Preservation Commission; in R1-2A, R2A and R3A districts outside the Greater Transit Zone; or in the Special Bay Ridge District west of Ridge Boulevard or south of Marine Avenue (ZR 114-02).
• Basement or cellar ADUs and backyard ADUs are not allowed in DEP's 10-year rainfall flood risk area or coastal flood risk area. DOB also lists FEMA's Special Flood Hazard Area.
• In the high-risk flood zone, no ADU may be below the flood-resistant construction elevation. Above-grade ADUs in flood areas face added elevation requirements.

A garage conversion is not a backyard ADU under zoning, so converting an existing garage is not barred in the historic districts and low-density districts listed above. Where backyard ADUs are prohibited, the zoning does not let you legalize an ADU in a building that was already in a required yard or open space before December 5, 2024.

Check flood areas on DEP's Interim Flood Risk Area Map. [2][3][4][7]

Size, height and setbacks for backyard ADUs

A building in the rear yard that contains an ADU is limited to one story and 15 feet. If a parking space is provided below part of the building, the building and its ADU may be up to two stories or 25 feet above the adjoining grade, whichever is less, including the peak of a pitched roof.

The building can cover no more than one-third of the rear yard (or rear yard equivalent). A free-standing building must be at least five feet from the rear and side lot lines, and an ADU must be at least 10 feet from a one- or two-family home on the same lot. A backyard ADU must be reachable directly from a side yard or open area along a side lot line at least five feet wide, and DOB requires a five-foot clear path from the street for the Fire Department.

Detached ADUs must always have sprinklers. When you convert an existing garage, DOB says existing non-compliances such as setbacks may be kept. HPD says an ADU can't go in the front yard. [2][4][6][8][9][10]

Parking

You don't have to add parking for an ADU. In the Zoning Resolution's parking tables for the Outer Transit Zone (ZR 25-222) and beyond the Greater Transit Zone (ZR 25-232), the requirement for a dwelling unit that is an ancillary dwelling unit is 0 percent in every district. In the Inner Transit Zone and the Manhattan Core and Long Island City parking areas, no parking is required for new housing at all.

If you convert a legal attached garage or a garage inside the home, DOB says the parking may be omitted where the zoning allows it. [1][4][10][11][12]

Owner occupancy and renting

At the time an ADU is first occupied, the zoning lot must be the primary residence of an owner of that lot. HPD's Plus One ADU program adds longer residency rules for homes it finances; see the Plus One ADU section below. [2][4][10]

Two-family homes and the Multiple Dwelling Law

A two-family home can add one ADU. If you add it in the attic, basement or cellar, or as an attached addition, the building is treated as a three-family building under the state Multiple Dwelling Law, unless the ADU is separated by a fire wall. HPD warns that some Multiple Dwelling Law requirements, such as sprinklers or changes to ceiling heights, egress and room sizes across the whole building, may make a project infeasible.

The law does not apply when the ADU is fully detached, attached but separated by a fire wall, or a basement unit legalized through the pilot program. [3][4][10]

Basement and cellar ADUs

Outside the legalization pilot, an existing one-family home may convert its basement or cellar into an ADU that complies with Building Code Appendix U. A new one-family home can be built with a basement or cellar ADU if it meets the code requirements for two-family homes and DOB rule 1 RCNY 105-08; DOB says applications for a new one-family home with a cellar ADU are now accepted under that rule and Local Law 80 of 2026. That law, which took effect when it was enacted on April 9, 2026, lets an ADU in a cellar be rented once it has a certificate of occupancy or temporary certificate of occupancy. In a two-family home, a basement or cellar ADU makes the building R-2 and triggers the Multiple Dwelling Law.

Every habitable room needs a ceiling at least 7 feet high, and a cellar ceiling must be at least 2 feet above grade. All subgrade ADUs need sprinklers, radon and vapor mitigation, water sensors, emergency escape openings and a 1-hour fire separation from the main home. Basement and cellar ADUs are not allowed in mapped flood risk areas.

Legalization pilot (Local Law 126): existing occupied basement and cellar units in one- and two-family homes can be legalized over a 10-year compliance schedule if the unit existed before April 20, 2024, the owner applies before April 20, 2029, and the home is outside flood risk areas and inside the program area: Bronx community districts 9, 10, 11 and 12; Brooklyn 4, 10, 11 and 17; Manhattan 2, 3, 9, 10, 11 and 12; and Queens 2. DOB is not yet accepting applications (Authorizations for Temporary Residence) until its rules take effect. Illegal units outside the program area must be legalized the usual way and must meet code before anyone lives there.

Our basement apartment guide covers basement units in general. [3][4][6][13]

Pre-approved backyard ADU plans

DOB, HPD and the Economic Development Corporation run an online Pre-Approved ADU Plan Library on HPD's ADU for You site. Each plan is a backyard ADU design that DOB has reviewed for construction code and zoning compliance and FDNY has reviewed for sprinklers.

To use one, contact the registered design professional who created it. That professional files a standard application with DOB that cites the plan's numbers, and must still address site-specific items such as zoning, the foundation, exterior walls and DEP utility connections. DOB lists the approved plans on its Pre-Approved ADU page. [6][14][15]

Plus One ADU: city and state financing

HPD's Plus One ADU program offers low- or no-interest loans or construction grants, funded by New York State Homes and Community Renewal and HPD, and run with Restored Homes HDFC. Homeowners may earn up to 165% of area median income, with preference for those at 120% or below, must live in the home, and must be current on mortgages. Eligible homes have one or two existing units and, HPD says, must be outside the Special Coastal Risk District according to FEMA's flood zone designation.

HPD's FAQ (September 4, 2025) says homeowners can get an HCR grant of up to $175,000 and a city loan of up to $220,000, a combined $395,000 per property. A deferred-forgivable loan requires the ADU's rent to stay at 100% of area median income with yearly increases capped at 2%. Borrowers must keep the home as their primary residence for at least 10 years (15 under an HPD regulatory agreement), and program homeowners may not rent out both the home and the ADU.

Intake is closed. HPD says that as of June 12, 2026, intake for the program is closed while it reviews thousands of survey responses. You can join the Plus One ADU mailing list for updates. HPD warns that the program never charges for eligibility analysis or guidance.

If you don't qualify, you can still build on your own with a licensed professional who files plans and pulls DOB permits. For free technical help, HPD's ADU for You site lists the ADU hotline of Neighborhood Restore and its affiliate Restored Homes HDFC (the Plus One program administrator): (212) 584-8981, ext. 12. [5][10][15]

Permits and filing

ADUs are filed in DOB NOW: Build, with an NYC.ID account, as an Alt-CO-GC job when the ADU is in the same building, or a New Building-GC job when it is detached or separated by a fire wall. The PW1 form asks whether the work includes an ADU, the pre-approved plan number if any, the ADU's location and where its main entrance opens. ADU jobs can be filed as professionally certified, except legalization pilot units, which DOB's Central Development Unit must review.

All ADUs must meet Building Code Appendix U, except basement or cellar ADUs built with a new one-family home, which follow the NYC Construction Codes and rule 1 RCNY 105-08. For questions about a specific property, call DOB's customer service unit in your borough (listed below). [3][4][16]

State law and the rest of New York

New York City's ADU rules come from its own Zoning Resolution and local laws, plus the state Multiple Dwelling Law for buildings that become three-family. State money for ADUs in the city comes through the Plus One ADU program, funded by New York State Homes and Community Renewal (HCR) and HPD. For the rest of the state, see our New York State ADU page. [2][3][5][10]

Permit steps in New York City

1. Check what your lot allows

   Enter your address on HPD's ADU for You site to see what type of ADU may be possible. The ADU rules are in the Zoning Resolution; check whether you are in a flood risk area on DEP's Interim Flood Risk Area Map. The site says its information is educational, so confirm with DOB. [2][3][15]

2. Choose a design and hire a design professional

   Pick a custom design or a backyard ADU from the city's Pre-Approved ADU Plan Library on ADU for You. Either way, a registered design professional reviews your site and files the job; for a pre-approved plan you contact the professional who designed it. [6][14][15]

3. File in DOB NOW: Build

   Your design professional files in DOB NOW as an Alt-CO-GC job (ADU in the same building) or a New Building-GC job (detached ADU, or one separated by a fire wall), and answers the Ancillary Dwelling Unit questions on the PW1 form. A pre-approved plan still needs site-specific zoning and utility work. [3][4][14]

4. Build and pass inspections

   Build to the NYC Construction Codes and Building Code Appendix U, including the separate entrance, fire separation, emergency escape openings and, for most ADUs, sprinklers. [4][6]

5. Get the certificate of occupancy

   The certificate of occupancy must list the unit as an Ancillary Dwelling Unit per ZR 12-10 and Building Code Appendix U. When the ADU is first occupied, the lot must be the primary residence of an owner. [2][4]

Pre-approved and sample plans

• Pre-Approved ADU Plan Library

  Backyard ADU designs already reviewed by DOB for code and zoning and by FDNY for sprinklers; a design professional adapts one to your lot and files a standard application. [6][14][15]

Who to call

• ADU for You technical assistance (Neighborhood Restore and Restored Homes HDFC)

  Free help planning, financing and building a legal ADU; ADU hotline ext. 12; email aduforyou@neighborhoodrestore.org

  (212) 584-8981 ext. 12

  [1][15]

• HPD Plus One ADU Program

  Plus One ADU loans and grants; email PlusOneADU@hpd.nyc.gov

  Homeownership Opportunities & Preservation, 100 Gold Street, Room 9S-11, New York, NY 10038

  [5]

• DOB Bronx Borough Office

  Customer service for permits on Bronx properties; phone lines 8:30 a.m. to 4:30 p.m. weekdays

  (718) 960-4710

  1775 Grand Concourse, 5th Floor, Bronx, NY 10453

  [16]

• DOB Brooklyn Borough Office

  Customer service for permits on Brooklyn properties

  (718) 802-3675

  345 Adams Street, 3rd Floor, Brooklyn, NY 11201

  [16]

• DOB Manhattan Borough Office

  Customer service (1st floor) for permits on Manhattan properties

  (212) 393-2614

  280 Broadway, New York, NY 10007

  [16]

• DOB Queens Borough Office

  Customer service for permits on Queens properties

  (718) 286-7620

  120-55 Queens Boulevard, Kew Gardens, NY 11424

  [16]

• DOB Staten Island Borough Office

  Customer service for permits on Staten Island properties

  (718) 420-5400

  10 Richmond Terrace, 2nd Floor, Staten Island, NY 10301

  [16]

• Department of City Planning (City of Yes)

  Questions about the City of Yes for Housing Opportunity zoning; email HousingOpportunity@planning.nyc.gov

  [1]

Questions people ask