What Is an ADU, and Can I Build One in New York?
By Daniel Kidd AIA | May 29, 2026 | ADU Design, New York, Residential, Hudson Valley
ADU. The acronym shows up everywhere now in city planning documents, in conversations between neighbors, in the inbox of almost every architect practicing in New York. Most people asking about ADUs are starting from the same place: they've heard the term, they sense it might apply to their property, and they want a straight answer about whether they can build one.
Here's the honest answer: it depends enormously on where in New York you are. An ADU project in Brooklyn and an ADU project in Kingston are not the same undertaking. The zoning logic is different, the construction approach is different, the timeline is different, and the costs are different. I'll walk through both.
FAQs
What Is an ADU, Exactly?
An Accessory Dwelling Unit is a second, self-contained home on the same property as a primary residence. It has its own entrance, kitchen, and bathroom. It's not a spare bedroom it's a fully independent dwelling unit that happens to share a lot, or sometimes a building, with another one.
The three most common forms:
Detached ADU, a separate structure in the backyard, fully independent of the main house. Most common in suburban and upstate contexts where there's a lot of depth to work with.
Attached ADU, an addition to an existing home, connected structurally but with a separate entrance and self-contained living space.
Interior ADU, a conversion of existing space within the home: a basement, a garage, an unused floor. This is the most common form in New York City, where lot coverage and FAR make new construction difficult.
How Does the ADU Process Work in New York City?
In New York City, ADU development is governed by a combination of city zoning, the New York City Building Code, and, since 2023, Local Law 18, which expanded homeowners’ rights to create ADUs in basements, garages, and accessory structures.
The reality of building an ADU in the five boroughs is that every property is different, and the constraints are layered. Zoning determines what's possible in terms of size and placement. The Building Code determines what the unit must include: egress windows, ceiling heights, ventilation, and fire separation. And if your building is in a landmark district, the Landmarks Preservation Commission may have jurisdiction over any exterior changes.
What I tell NYC clients interested in ADUs: start with a feasibility study. Before spending anything on design, you need to know what your specific property and zoning allow. The rules vary by district, by lot size, and by what's already built on the property. A feasibility study takes two to four weeks and gives you a clear picture before you commit.
Typical costs for an NYC ADU:
Basement conversion: $150,000 – $300,000
Garage conversion or interior renovation: $120,000 – $250,000
Small attached addition: $250,000 – $450,000+
Timeline from design to certificate of occupancy: typically 12 to 18 months, sometimes longer if landmark review is involved.
How Is Building an ADU Upstate or in the Hudson Valley Different?
Upstate New York and the Hudson Valley are a completely different context and, in many ways, a more straightforward one for ADU development.
Most municipalities in this region have been loosening ADU restrictions in response to housing demand and state-level pressure. Lot sizes are larger, setback requirements are less constrained, and the approval process, while still real, is generally faster than navigating the NYC DOB.
The most common form upstate is the detached ADU: a new structure in the backyard or on a larger rural property. The design challenge is creating genuine spatial independence for both the primary home and the ADU privacy, separate arrival, distinct outdoor space without the two living on top of each other.
In 2023, PLANS won the City of Kingston's ADU design competition with L'ADU, a 460 sqft detached unit organized around a private courtyard. The design was built around a specific constraint: how do you give two households genuine independence on a standard residential lot? The answer was the courtyard, a small outdoor room that belongs exclusively to the ADU, creating a sense of arrival and privacy that makes the unit feel like a home rather than an addition.
The Kingston pre-approved plans are publicly available for download from the city website, specifically to reduce the barrier for homeowners who want to build. That's worth knowing if you own property in Kingston.
Typical costs for an upstate ADU:
Simple detached structure, modest finish: $150,000 – $280,000
New detached structure, higher finish: $250,000 – $450,000
Garage or barn conversion: $80,000 – $180,000
Timeline from design to certificate of occupancy: typically 8 to 14 months, depending on municipality and contractor availability.
Why Do People Build ADUs?
The reasons are usually one of three things:
Rental income. A well-designed ADU on a property in the Hudson Valley can generate meaningful rental income enough to materially offset carrying costs. Upstate short-term rental markets are strong, and a thoughtfully designed unit commands a premium over a converted garage.
Multigenerational living. An aging parent who wants independence but proximity. An adult child who can't yet afford their own place. An ADU solves the problem without requiring anyone to give up privacy.
Long-term flexibility. Today it's a rental. In five years it's a home office. In ten, it's housing for a family member. A well-designed ADU adapts.
Where Should You Start?
The first question, in both contexts, is whether your property and zoning actually allow an ADU, and if so, what type and what size. That's a feasibility question, not a design question. It's the right thing to resolve before spending money on drawings.
At PLANS, we've designed ADUs in New York City and across the Hudson Valley. If you want to understand what's possible on your property, that's exactly the conversation we start with.
Reach us at info@plans.nyc