DOB has launched an online application for owners of one- or two-family dwellings who want to modify the basements, backyards, attics, and free-standing or attached structures on their property lots into so-called ancillary dwelling units (ADUs) that can be rented out to tenants. 

The website application was made available after DOB published long-awaited rules that will govern ADUs. ADUs are a component of City of Yes, the city’s zoning code rewrite enacted under Local Laws 126 and 127 of 2024 to provide for new housing accommodations citywide. 

Homeowners can access the ADU For You program online at www.nyc.gov/site/hpd/services-and-information/adu-for-you.page, which offers guidance and pre-approved designs for ADUs. Additional information on Accessory Dwelling Units is provided on DOB’s website at www.nyc.gov/site/buildings/codes/adu.page.

Local Laws Now Permit ADU Legalization

Under Local Law 126 of 2024, existing occupied basement and cellars in existing one- and two-family buildings that are in the program area and not in a flood risk zone may be converted into a legal habitable dwelling. The unit must exist prior to April 20, 2024. Subgrade ADUs under the Legalization Program may continue to be occupied so long as they meet each milestone and update the Authorization for Temporary Residence after meeting each milestone. These buildings must comply with the compliance timeline outlined in Local Law 126, based on the date of initial Authorization for Temporary Residence (ATR) certification

How to File an ADU Application in DOB NOW

To submit an ADU filing, login to DOB NOW at https://a810-dobnow/publish/index.html#!/ using an NYC.ID account and create either an Alt-CO-GC or New Building-GC job. In the PW1: Plan/Work Application tab, a new Ancillary Dwelling Unit section appears under Filing Review Type, Work Type/Filing Includes. Applicants must answer whether the scope of work includes an ADU. If Yes is selected, additional fields will appear: pre-approved plan number, ADU location, and where the main entrance of the ADU directly opens. The Schedule of Occupancy has also been updated to include Ancillary Dwelling Unit as a Description of Use option for Residential Occupancy Classification under both Occupancy Group R-2 and R-3. 

New Cellar ADU Applications Not Currently Accepted

As of Sept. 30, 2025, DOB’s ADU webpage notes that applications for legalization and new cellar ADUs are not currently being accepted pending NYC Housing Maintenance Code amendment and promulgation of DOB rules.  

ADU Requirements

To qualify, general requirements of ADUs include the following:

• There can be only one ADU for each one- or two-family residence.
• At the time of initial occupancy for an ADU, the zoning lot on which the ADU is located must be the primary residence of an owner of that zoning lot.
• The maximum zoning floor area is 800 square feet.
• ADUs must have a separate entrance.
• A two-family building adding an attic, basement, cellar, or attached ADU will be treated as a three-family building subject to the NYS Multiple Dwelling Law (MDL), unless the unit is separated by a fire wall.
• A two-family building with a pre-existing basement or cellar unit undergoing the legalization process will be subject to Building Code Appendix U and additional fire and safety rules and regulations in lieu of the MDL. Legalization applications are not currently being accepted until the DOB Rule pursuant to Local Law 126 is promulgated and effective.

Exceptions to permitting ADUs include:

• Backyard ADUs are not permitted in:
  • Historic Districts;
  • R1-2A, R2A, and R3A districts outside of the Greater Transit Zone; and
  • Special Bay Ridge District west of Ridge Boulevard or south of Marine Avenue.
• Subgrade ADUs are not permitted in high-risk flood areas demarcated by FEMA’s Special Flood Hazard Area, the Coastal Flood Risk Area, and DEP’s 10-Year Rainfall Flood Risk Area.