NYC ADU Regulations 2025: What Homeowners Need to Know
In 2025, New York City officially legalized Accessory Dwelling Units, also known as Ancillary Dwelling Units or ADUs. No more gray-market basement apartments or “don’t ask, don’t tell” agreements. The city has finally set clear, legal guidelines for developing second homes on your property.
Before you start designing backyard cottages or knocking down basement walls, it’s important to understand what the new rules actually allow.
Who Can Build an ADU in NYC in 2025?
Under the new 2025 legislation, owners of single- or two-family homes are eligible to develop an Accessory Dwelling Unit (ADU). Only one ADU is permitted per lot.
Here’s the catch: you must live in the primary dwelling unit or the ADU in order to receive Certificate of Occupancy for the new ADU.
In other words, you can’t buy a home in Queens, build an ADU in the backyard, and rent out both units while you move to Jersey. At least not until after you receive Certificate of Occupancy for the ADU.
What Types of ADUs Are Allowed?
An “ADU” no longer just means a basement with a hot plate and folding bed. NYC now recognizes four primary forms of legal ADUs:
Basement or cellar units
Attached units in one-family homes, including attic conversions
Attached units in two-family homes (no attic conversions allowed)
Backyard cottages, also known as detached ADUs or “tiny houses”
Yes, you read that right, attics can legally be converted after decades of restrictions. And backyard tiny homes? They’re no longer just a Portland fantasy. They’re coming to Staten Island, Queens and beyond.
All ADUs must meet specific building, safety, and accessibility standards, but the city is encouraging development through its “City of Yes” housing plan and the “ADU for You” initiative.
Size, Design, and Visibility Rules
Don’t plan on creating a 1,500-square-foot guest palace. In NYC, the maximum allowable size of an ADU is 800 square feet. Your design will also be limited by zoning regulations and property lot characteristics.
Visibility is another requirement: if your ADU’s entrance isn’t visible from the street, you must install a sign with red letters at least five inches high to mark the entrance. It’s not for aesthetic, it’s for first responders’ safety.
Backyard cottages are also subject to setback, height, and open-space requirements. Your architect will handle these details, but it’s worth knowing upfront that you can’t just place a tiny home anywhere, like directly on your property line.
You Must Get a Certificate of Occupancy
This isn’t optional. Like any new construction, no one can live in your ADU until your property has received a Certificate of Occupancy (CO) from the Department of Buildings.
That means passing structural, electrical, plumbing, and fire inspections, and proving the unit is habitable (with proper ventilation, heating, and egress).
An ADU without a CO is illegal, uninsurable, and un-rentable.
How to Apply
As of September 30th, 2025, NYC has begun accepting ADU applications through the DOB NOW: Build online portal, a centralized platform for submitting plans, paying fees, and tracking permits.
Ready to “submit”? You’ll still need a licensed architect or expediter to prepare compliant construction documents. The city will reject amateur or incomplete submissions, and delays here can set you back months.
Why This Matters (Beyond Extra Rent)
Sure, an ADU can generate $1,500–$3,500 per month in rental income. But the real value lies in flexibility.
Maybe you have an elderly parent who needs nearby but private living space. Maybe your adult child is saving for a down payment. Maybe you want a quiet, dedicated home office. Or maybe you simply believe that more housing means a healthier, more resilient city.
Whatever your reason, the new 2025 ADU rules finally give you a legal and supported way to do it, without the risk of fines, evictions, or midnight DOB inspections.
Final Thoughts
Still need more information? NYC is planning on offering technical assistance through new ADU support programs such as the ADU for You initiative. Take the time to learn, talk with your neighbors, and hire the right people. Because a great ADU isn’t just an extra room. It’s passive income in your own backyard.