A Quick & Simple Guide to Understanding NYC's ADU Rules

What Is an Accessory Dwelling Unit?

An accessory dwelling unit, or ADU, is a small, self-contained home built on the same lot as your main house. It needs its own kitchen, bathroom, and sleeping area, and its own separate entrance. An ADU can take a few different forms. It can be carved out of an existing basement or cellar, added in an attic, built as an addition attached to your home, or constructed as a brand new detached structure in your backyard.

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Does Every Homeowner Qualify?

This is the part that gets glossed over in a lot of coverage. The short answer is no, not every property qualifies, and the restrictions are more significant than many homeowners expect.

To even be in the running, your property needs to be a one or two family home, and the lot can only have one ADU total. If a property already has an ADU, you cannot add a second one. You also have to actually live there. At the time the ADU is first occupied, the lot needs to be the primary residence of the owner, whether that means living in the main house or living in the ADU itself.

Beyond that, your zoning district and lot type matter quite a bit. Backyard, detached ADUs are not allowed in historic districts, are restricted in certain lower density zoning categories unless you are within what the city calls the Greater Transit Zone, and are blocked in a specific part of Bay Ridge.

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What About Basement and Cellar Apartments That Already Exist?

This is a separate and important piece of the puzzle, and it works differently than new construction. A lot of NYC homeowners already have a basement or cellar apartment that has been occupied for years without being legal. Local Law 126 created a pilot program specifically to bring some of those existing units into compliance over time, rather than forcing an all at once fix.

The city has not yet finalized the specific Department of Buildings rules for this pilot program, so applications for it are not currently being accepted. If you have an existing basement unit and you are hoping to use this route to legalize it, you can start gathering documentation now, but you cannot file yet. Keep an eye on the Department of Buildings ADU page for updates, since this is expected to open up as the rules get finalized.

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What If I Want to Build a New ADU From Scratch?

The application process for new ADUs is already open. You file through the city's standard permitting system, called DOB NOW: Build. You will need a registered architect or licensed engineer to prepare your plans and file for you.

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Here are the basic size and structure rules:

• Your ADU cannot be larger than 800 square feet.
• A detached structure cannot cover more than a third of your required rear yard.
• There is no minimum size, but the unit still has to meet the city's basic room size standards.
• Adding an ADU to a two family home usually makes it a three family building under state law, unless the new unit has its own fire wall. Three family buildings follow different code rules, so ask your architect about this early.

One piece of good news: you will not need to add a parking space just because you are adding an ADU. The city dropped that requirement. For official guidance and updates on NYC ADU rules and permitting, visit the NYC Department of Buildings ADU page.

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Disclaimer: This content is intended for informational and educational purposes only and is not intended to be construed as legal, tax, financial, or insurance advice. Every property and tax situation is unique. Please consult a licensed attorney, CPA, or tax professional regarding your specific circumstances before making any decisions related to property improvements, tax assessments, or real estate transactions. Mohammed M. Rahman is a licensed real estate broker in New York. Contact: Mo@ClosedByMo.com.