Can I Build an ADU in My Backyard in NYC?

Tapasya Wancho
Apr 28
4 min read

Modern blue house with large windows, warm interior lighting. Surrounded by tall trees and landscaping in autumn colors, under a clear sky.

As Accessory Dwelling Units(ADU) become legal across much of New York City, many homeowners are asking a simple question: Can I build an ADU unit in my backyard?

Thanks to recent zoning changes, adding a small, separate ADU home to your property is now possible — but there are still important limits based on your lot, zoning district, and location.

In this article, we’ll break down everything you need to know to determine whether your property qualifies for a detached backyard ADU. We’ll cover allowed property types, zoning blockers, yard size rules, and introduce tools like the NYC Zoning & Land Use Map and FEMA Flood Map Service Center to check your building site.

Not sure where to start? Schedule a free consultation with Nook, and we’ll help you figure out if your lot is eligible and what your options are.

What Is a Backyard ADU?

A backyard ADU is a detached housing unit located behind the main house on a residential lot. Unlike basement apartments or garage conversions, this type of ADU home is a fully separate structure, offering more privacy and flexibility for extended family, guests, or renters.

Common backyard ADUs include prefabricated cottages, modular units, or small custom-built homes, typically up to 800 square feet. Each has its own kitchen, bathroom, and entrance.

If you’re new to the topic, check out Nook’s ADU Guide for an overview of how these small homes are reshaping housing options in New York City.

Who Is Eligible to Build a Backyard ADU in NYC?

Even though backyard ADUs are now permitted under NYC’s updated building code, only certain properties qualify. To be eligible:

The property must be a single-family or two-family home
The homeowner must live on the property (owner-occupancy is required)
Only one ADU unit is allowed per lot
The unit must be no larger than 800 square feet
It must be located in the rear yard and comply with minimum distance requirements from lot lines and other buildings

Backyard ADUs also require a separate entrance and must follow fire and building code standards related to safety, utilities, and accessibility. These rules are designed to maintain privacy, limit overcrowding, and ensure safe living conditions for both the main home and the ADU.

You can view the full list of eligibility requirements in Appendix U of the NYC Building Code.

Common Zoning Limitations

While backyard ADUs are legal in many areas, zoning is often the biggest barrier for NYC homeowners. Here are some common restrictions to be aware of:

Zoning districts that often block ADUs:

R1A, R2A, and R3A zones generally prohibit ADUs unless the property is located in a Greater Transit Zone
Historic districts usually do not allow exterior additions or detached structures
Flood-prone areas, especially those classified as Special Flood Hazard Areas, are restricted due to safety concerns

Rear yard limitations:

Detached ADUs must maintain minimum clearance from rear and side lot lines, usually at least five feet
If your home is attached to neighboring houses, like in many rowhouse-style blocks, you may not have the required rear yard access or space to build a separate unit
Height limits apply: most ADUs must be no taller than 15 feet, or 25 feet if built over an enclosed parking area

Lot size and space constraints:

Some smaller properties may exceed their floor area ratio (FAR) by adding an ADU
NYC also enforces minimum yard depth requirements, which can limit buildable space in smaller or irregular lots

To check your property’s zoning, use the official NYC Zoning & Land Use Map. It’s free and includes search by address, zoning designation, and special district overlays.

How to Know If Your Backyard Qualifies

Before making any plans, it’s important to confirm whether your property meets the requirements for a backyard ADU. Start by checking:

Your zoning district (e.g. R3A vs. R4)
Your lot size and shape, especially depth
Whether your home is in a flood zone or a landmarked area

You can research this using free tools like:

Even with these tools, NYC zoning can be complicated. If you're unsure about your eligibility, it’s worth getting a quick professional review. Schedule a free consultation to get clarity before you commit to anything.

What If My Lot Doesn’t Qualify?

If your backyard isn’t eligible for a detached ADU, you still have other options for adding a legal secondary unit. Depending on your property layout and zoning, you might consider:

A basement or cellar conversionAn attached unit addition to the rear or side of your home
A second-story extension over an existing garage or accessory structure

These configurations are often more feasible in tight urban lots and can still provide the flexibility of a separate living space.

Next Steps: Get Help from Nook

Navigating NYC’s zoning code isn’t easy — and most homeowners shouldn’t try to figure it out alone. Whether you’re dealing with lot size questions, rear yard limitations, or historic district restrictions, the rules can be complex and case-specific.

Nook simplifies the entire process, from start to finish. Our team handles: