Yes. As of October 2026, every new ADU in New York City is filed with the Department of Buildings through DOB NOW: Build. A unit inside the existing building is an Alteration CO job; a detached unit, or one separated by a firewall, is a New Building job. The finished ADU appears on an updated certificate of occupancy.
Who prepares the filing?
Plans are prepared and filed by a registered design professional, a New York-licensed architect or engineer. DOB reviews pre-approved designs from licensed design professionals for its Pre-Approved Plan Library, and owners who choose one can hire the professional who created it.
What are the main steps?
- Eligibility check: building type, zoning district, flood maps, historic and special districts.
- Design to the Zoning Resolution and Appendix U of the Building Code.
- Filing in DOB NOW as Alt-CO or New Building, with professional certification allowed for most ADUs.
- Construction under permit, with inspections.
- For basements and cellars, DOHMH radon and vapor certification before a temporary certificate of occupancy.
- A new or amended certificate of occupancy noting the ADU.
What other approvals can apply?
- LPC review for exterior work in a historic district.
- Multiple Dwelling Law requirements when an ADU makes a two-family house a three-unit building.
How long does it take?
HPD's guidebook says an ADU can take anywhere from two months to two and a half years from design to completion, and advises planning a flexible timeline. Interior conversions with complete filings tend to be at the short end.
Sources, as of October 2026:
- NYC DOB announcement, September 30, 2025, and ADU FAQs.
- NYC DOB rule 1 RCNY 105-08.
- NYC HPD, ADU guidebook.