DOB to Begin Accepting NYC ADU Permit Applications

Breaking news in the ADU world - NYC’s Department of Buildings (DOB) will now begin accepting permit applications for ADUs! We recently shared an update that DOB was putting a pause on ADU permit filings while two city rules related to ADUs were being finalized. The rules were officially signed into law on September 30th, 2025, giving property owners, architects and ADU contractors the green light to proceed.

The final version of the DOB’s Accessory Dwelling Unit Rule included five changes based on public comments, including two suggestions made by Second Key. The DEP Flood Map Rule was adopted with no changes from the proposed rule.

Mayor Adams Loves ADUs

We previously predicted that the DOB and DEP rules pertaining to ADUs would not go into effect until November or December 2025, but Mayor Eric Adams had other plans. Most city rules take 3 to 4 months to be adopted, plus another 30 days between rule adoption and effective date. However, Mayor Adams approved requests to waive the typical 30-day waiting period for new rules, citing NYC’s desperate need for more housing. The Mayor’s office is also spearheading the ADU for You resource portal, which will provide resources and guides to building an ADU in NYC. This is great news for single family and two-family homeowners in NYC.

Cellar ADU Conversions in NYC

Unfortunately, the wait continues for those interested in cellar ADU conversions. According to the DOB website, “Legalization and new cellar ADU applications are not currently being accepted until the NYC Housing Maintenance Code (HMC) amendment and DOB Rules are promulgated.” While not explicitly stated by DOB, we can also assume this proposed rule from New York City’s Department of Health and Mental Hygiene related to radon and vapor testing must be signed into law before DOB will accept cellar ADU conversion filings. There is no timeline for when cellar ADU applications will be accepted by DOB.

What’s Next for NYC ADUs?

With the exception of cellar ADU conversions, NYC property owners can now begin filing ADU permit applications. Based on our conversations with current NYC property owners, and analysis of nationwide ADU trends, we anticipate that Accessory Dwelling Units in New York City will be in high demand moving forward.

Second Key is here to guide you every step of the way. Let’s unlock the full potential of your NYC property—seamlessly, smartly, and beautifully.

Start your ADU journey today with a free property assessment.