What's Required in New York City
- One ADU per 1- or 2-family residence, maximum 800 sq ft of zoning floor area, with a separate entrance (DOB ADU page)
- At initial occupancy, the zoning lot must be the primary residence of an owner
- Detached units: 2 stories or 25 ft, 5 ft from lot lines, 10 ft from other buildings, rear-yard coverage limited to 50%, within 100 ft of the curb with a 5-ft access path (DCP City of Yes guide)
- Not allowed: backyard ADUs in historic districts, the Special Bay Ridge District and certain low-density R districts outside transit zones; basement or cellar ADUs in FEMA flood zones and DEP rainfall flood-risk areas; any ADU in Special Coastal Risk Districts
- Filed in DOB NOW: Build by a PE or RA as Alt-CO-GC or New Building-GC with the Ancillary Dwelling Unit section of the PW1 completed
- A two-family home adding an ADU becomes three-family under the NYS Multiple Dwelling Law unless separated by a firewall
- Plumbing by a Licensed Master Plumber and wiring by a Licensed Master Electrician, each under permit
- Existing basement apartments: ATR pilot under Local Law 126 of 2024, apply before April 20, 2029 (applications not yet open per DOB)
Can You Build an ADU in New York City?
Yes, since the City of Yes for Housing Opportunity zoning amendment and Local Laws 126 and 127 of 2024. DOB's Ancillary Dwelling Unit page sets the frame: one ADU per one- or two-family residence, a maximum of 800 square feet of zoning floor area, a separate entrance, and at the time of initial occupancy the zoning lot must be the primary residence of an owner. The unit may be an attic, basement, cellar, a free-standing building in the yard, or an addition attached to the house. Backyard ADUs are prohibited in historic districts, in certain low-density R districts outside transit zones, and in the Special Bay Ridge District; basement and cellar ADUs are barred in FEMA flood zones and DEP rainfall flood-risk areas. A two-family home that adds an ADU becomes a three-family building and falls under the State Multiple Dwelling Law unless the units are separated by a firewall.
NYC ADU Permit Rules by Scenario
| What you are doing | DOB filing | Rule |
|---|---|---|
| Detached backyard cottage (up to 800 sq ft, 2 stories or 25 ft, 5 ft from lot lines, 10 ft from other buildings) | New Building filing (NB-GC job type) in DOB NOW | DOB ADU page; DCP City of Yes ADU guide |
| Garage conversion, attached addition, attic or basement unit | Alteration-CO (Alt-CO-GC job type) for an amended Certificate of Occupancy | DOB ADU page |
| Basement or cellar unit in a FEMA flood zone or DEP rainfall flood-risk area | Not permitted | DOB ADU page |
| Backyard unit in a historic district, the Special Bay Ridge District, or a low-density district outside a transit zone | Not permitted | DOB ADU page |
| Legalizing an existing basement or cellar apartment in an eligible community district | Authorization for Temporary Residence (ATR) pilot; apply before April 20, 2029; then an alteration for an amended CO | DOB press release; Local Law 126 of 2024 |
| Kitchen and bathroom plumbing for the unit | Licensed Master Plumber; plumbing permits within the job | DOB Plumbing Permits page |
| Wiring the unit | Electrical permit by a Licensed Master Electrician | DOB Electrical System owner requirements |
How Much Does an ADU Permit Cost in NYC?
The DOB filing fee comes from Administrative Code Table 28-112.2 (as amended by Local Law 128 of 2024, in effect since December 21, 2025). A detached cottage is a new building at a one-, two- or three-family dwelling: $0.06 per square foot of floor area, but not less than $130, so an 800-square-foot cottage files at about $130, the minimum, and a filing that retains existing building elements uses the alteration formula instead. A conversion or addition is an Alteration Type 1 at a one- to three-family home: $170 minimum covering the first $5,000 of job cost, plus $2.60 for each additional $1,000; a $120,000 basement conversion therefore files at about $469. Because the work changes the certificate of occupancy, half of the fee is due with the application and the balance before the permit. Those figures are DOB's only. The design professional, the plumber's and electrician's permits, and any Department of City Planning or Landmarks review are separate, and DOB's page lists no ADU-specific fee.
The Zoning Rules in One Place
The Department of City Planning's City of Yes guide lists the ADU parameters: one ADU per one- or two-family building with a maximum size of 800 square feet, counted as residential floor area, no parking requirement, a 2-story and 25-foot height limit for a detached unit, 5 feet from the lot line, 10 feet between a detached ADU and other buildings, rear-yard obstruction limited to 50 percent yard coverage, and a detached unit within 100 feet of the street curb with a 5-foot-wide access path. ADUs are not allowed in Special Coastal Risk Districts, and basement ADUs are not allowed in coastal flood areas. The ADU does not count toward the maximum number of units or the dwelling unit factor.
Who Files an ADU in New York City?
A Registered Design Professional (PE or RA) files in DOB NOW: Build using an NYC.ID account, choosing the Alt-CO-GC or New Building-GC job type and completing the Ancillary Dwelling Unit section of the PW1 with the unit's location and entrance. The permit is issued to a Registered General Contractor, with a Department of Consumer and Worker Protection Home Improvement Contractor license required at one- to four-family homes. Plumbing goes through a Licensed Master Plumber and wiring through a Licensed Master Electrician. The ATR legalization program for existing basement and cellar apartments is separate: as of DOB's page, applications are not yet being accepted pending rule promulgation, and the deadline to apply is April 20, 2029.
How to Get a ADU Permit in New York City
Confirm the lot qualifies
1- or 2-family home, owner-occupied lot, no existing ADU, not in an excluded district or flood zone for the unit type you want.
Hire a PE or RA
The design professional sizes the unit to 800 sq ft and the height and yard rules, and prepares the DOB NOW filing.
File the right job type
New Building-GC for a detached cottage ($0.06 per sq ft, $130 minimum); Alt-CO-GC for a conversion or addition ($170 minimum plus $2.60 per $1,000 of job cost over $5,000 at a 1-3 family home).
Pull the trade permits
Permit to a Registered GC with a DCWP HIC license; plumbing by a Licensed Master Plumber; electrical by a Licensed Master Electrician.
Inspections and the new Certificate of Occupancy
DOB inspects and signs off; the amended or new CO is what makes the unit legal to occupy.