ADU – Ancillary Dwelling Unit that can be built legally by a NYC homeowner
An Ancillary Dwelling Unit (ADU), also called an Accessory Dwelling Unit, is a small, separate apartment on the same property as the main home. It can be used for family members or tenants to live in, and it can bring extra money to the owner if it is rented. An ADU can be created inside the existing house, or it can be built as a small, separate building in the yard.
In this definition, the words “ancillary” and “accessory” mean “extra but connected.” The ADU is not the main home, but it is an extra living space that belongs to the same property and supports the main home, for example by giving space for family or helping pay the mortgage with rent.
Common types of ADUs include:
- Detached backyard unit
- Basement apartment
- Attic conversion
- Attached addition
- Converted garage
The Plus One ADU program benefits
The Plus One ADU program can help a typical NYC homeowner build or legalize a small extra apartment on their property, like a basement unit or backyard cottage, with strong technical support and up to about $395,000 in combined city and state financing for design and construction. This extra unit can give stable rental income, help pay the mortgage or taxes, and create safe, legal housing for family or tenants in a city with high housing costs.
How hard is it for a typical NYC homeowner to benefit from this program
However, it is hard for many owners to get into the program or keep the funding. Homeowners must live in a one‑family house as their primary residence, stay under strict income limits, show tax returns and pay stubs, have valid insurance, and clear most existing DOB or HPD violations before or during the project. They must also accept inspections, rent limits on the new ADU, possible loan repayment terms, and a long, complex process with applications, fees, paperwork, and construction rules that can make the program feel very restrictive for an average small homeowner.
The barriers of this program – why they are hard to cross.
For many small homeowners, the Plus One ADU program looks attractive on paper but quickly becomes overwhelming once they see the real‑life requirements. A one‑family homeowner must first confirm that the property is in an eligible area and that the house is a legal one‑family home in DOB records. Then they must review their income, debts, and existing violations to see if they are even likely to qualify before they start a full application.
The biggest barriers often include: strict income limits, a high level of documentation, and the need to resolve open DOB or HPD violations. A homeowner who already has illegal work in the basement, missing permits, or serious housing code issues may need to spend time and money fixing those problems before the new ADU work can even start. For someone who is already struggling with mortgage payments or property taxes, this step alone can stop the project.
Another challenge is the amount of time and attention the program requires. The owner must answer questions from the program team, collect papers from their employer, tax preparer, bank, and insurance company, and respond to city inspectors or project managers during design and construction. For a homeowner who works full‑time, has limited English, or is not comfortable with forms and official letters, this can feel like a second job. Some people start the process and then give up because it is too stressful or confusing.
Finally, the long‑term rules attached to the financing can also be a barrier. The homeowner must accept that the ADU will be subject to rent limits and other affordability rules for many years. This means they cannot simply charge whatever rent the market allows, even if prices go up. For owners who think of the ADU mainly as a way to maximize income, these restrictions may make the program less attractive, even if the construction money is generous.
What should a homeowner do to be able to build an ADU on their property?
A NYC homeowner who is thinking about building an ADU through the Plus One program should treat it as a step‑by‑step project, not just a construction idea. First, they should carefully read the official Plus One ADU information from HPD and check whether their property type and location are eligible. Next, they should gather basic documents that the program will almost certainly ask for: recent tax returns, proof that they live in the house (such as utility bills), proof of income, and information about any existing mortgages or liens.
Before applying, the homeowner should also look up their property in the NYC Department of Buildings and HPD online systems to see if there are open violations or illegal conversion issues. If there are serious problems, it is often better to speak with an architect, engineer, or code consultant to understand what must be corrected first. Once they have a basic picture of their situation, they can submit an interest form or application through the HPD Plus One portal and be ready to answer questions from program staff.
During the process, the homeowner should:
- Respond quickly to emails and letters from HPD or the program team
- Keep copies of everything they send
- Ask for explanations in plain language if they do not understand any term or requirement
If English is not their first language, it may help to ask a trusted family member, friend, or local community group to assist with reading documents and filling out forms. Finally, the homeowner must be prepared for inspections, design meetings, and construction disturbances. Building an ADU is a multi‑month or multi‑year effort, so planning ahead and keeping good records can make the experience more manageable and less stressful.
Official sources
You can read more about how the program works and who it is meant to help on the NYC HPD Plus One ADU pages:
If you see any capital letter abbreviations on this page or in an official letter you received from the city and you do not understand them, you can try to look them up on our Violation Codes page with the search tool.
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