An ADU (Accessory Dwelling Unit) is a secondary living space located on the same property as a primary home. In New York City, these units are officially known as Ancillary Dwelling Units. They can be created by converting a basement or attic, adding to the main home, garage conversion, or building a freestanding structure in the backyard.

In December 2024, New York City updated its zoning laws via the City of Yes for Housing Opportunity to allow many one- or two-family property owners to build an ADU. Eligibility depends on your zoning district, lot size, and site conditions. The best way to find out if your property qualifies is to request a free ADU assessment from our team.

Assembling the right team is crucial to the success of your ADU project. Second Key is a licensed general contractor specializing exclusively in NYC ADUs — we manage everything for you, from zoning analysis and design to DOB permitting and construction. Our turnkey approach is a time-saving alternative to assembling your own team of consultants, architects, engineers, and contractors. We guide homeowners across Queens, Brooklyn, Staten Island, and the Bronx through every step of the process.

The maximum size of an ADU in NYC is 800 square feet, and the height is limited to one floor, unless there is a garage or parking on the ground floor. ADU size and placement depend on your property’s zoning district, lot size, and site conditions. We’re here to help you understand exactly what’s allowed on your site.

Our typical detached ADU model ranges from $300 to $350 per square foot, depending on size, layout, site conditions, and finishes. Most projects fall between $150,000 and $400,000 total. Garage conversions and other ADU types may vary. Final pricing is confirmed after plans are approved by the NYC Department of Buildings. We provide detailed project estimates during your ADU Feasibility Study.

Construction of most ADUs in NYC takes 3 to 6 months, depending on size and complexity. The permitting and DOB approval process typically adds several months to the overall timeline, so homeowners should plan for a total project duration of 9 to 14 months from start to certificate of occupancy. We'll give you a more specific timeline estimate during your ADU Feasibility Study.

Yes. All ADUs require approval from the NYC Department of Buildings (DOB), including architectural and engineering plans, zoning analysis, and a final Certificate of Occupancy before the unit can be legally occupied. The permitting process is one of the more complex parts of an ADU project — Second Key manages it entirely on your behalf, so you don't need to navigate the DOB on your own.

Yes. Once your ADU has received a Certificate of Occupancy from the NYC Department of Buildings, it can be legally rented as a long-term unit. A well-finished ADU in NYC can generate $1,500 – $3,000+ per month depending on your borough and neighborhood. Note that short-term rentals (such as Airbnb) are heavily regulated in NYC and are generally not a practical option for ADU owners. Long-term rentals offer a more straightforward path to rental income.

Yes. Converting an existing garage into an ADU is one of the most popular and cost-effective options — you're working with an existing structure, which can simplify permitting and reduce construction costs. Second Key handles garage conversion projects across Queens, Brooklyn, Staten Island, and the Bronx.

Yes. There are several financing options available to NYC homeowners. The Plus One ADU Program, offered by the city, provides eligible owner-occupants with up to $395,000 in combined grants and low-interest loans. Plus One ADU applications are currently open through June 12, 2026. Beyond that, many homeowners use HELOCs, construction loans, or ADU-specific lending products. Second Key works with reputable lending partners and can connect you with financing options during your free assessment.

The City of Yes for Housing Opportunity is a package of zoning reforms adopted by New York City in December 2024. It legalized ADU construction in NYC, allowing many one- and two-family homeowners across all five boroughs to build an ADU where it wasn't previously permitted. It's the reason this is such an important moment to explore your options.

Yes, but not permanently. To build an ADU under current NYC zoning rules, you must be an owner-occupant as a condition for receiving a Certificate of Occupancy. When applying for a Certificate of Occupancy, you must submit evidence of owner-occupancy. However, after receiving the Certificate of Occupancy, you may change your primary residence to another location.

Properties in Landmarks Preservation Commission (LPC)-designated historic districts face additional restrictions. New detached rear-yard ADUs are generally not permitted in LPC historic districts unless converting an existing structure. We can assess your specific situation with a free ADU assessment.

We serve homeowners across all five boroughs, including Queens, Staten Island, Brooklyn, the Bronx, and Manhattan.

The Plus One ADU Program is a New York City financial assistance initiative that provides eligible homeowners with up to $395,000 in combined grants and low-interest loans to help cover the cost of building an ADU. Applications reopened in March 2026. We can help you understand if you qualify and how to apply.

Generally, yes. Adding a permitted, legal ADU adds livable square footage and rental income potential to your property, both of which increase market value. The exact impact depends on your location, ADU size, and local market conditions.

When you add an ADU to your property, the NYC Department of Finance treats it as a physical increase in property value. Only the value of the ADU itself is assessed — your existing home is not fully reassessed. The increase in taxes is typically modest relative to the rental income potential, with an estimated monthly increase ranging from $100 to $150 per month.

Rental income varies by borough, neighborhood, and ADU size, but a well-finished ADU in NYC can realistically generate $1,500 to $3,000+ per month as a long-term rental. We're happy to walk through realistic projections for your area during your free ADU assessment.

An ADU assessment or feasibility assessment is a free evaluation Second Key conducts to determine whether your property qualifies for an ADU and what type of unit is possible. We review your zoning district, lot size, site conditions, and any applicable restrictions, then walk you through your options. Our free ADU assessment is perfect for initial eligibility screening but it is not a substitute for professional zoning analysis.

In many cases, yes. Detached backyard ADU construction typically does not require you to vacate your home. Interior conversions such as basements, attics and attached ADUs may require you to vacate the property during construction. We'll walk you through what to expect during construction at your project kickoff.

A Certificate of Occupancy (CO) is an official document issued by the NYC Department of Buildings confirming that a structure is safe and legally compliant with building code rules for its intended use. Your ADU must receive a CO before it can be legally occupied or rented.

The most common ADU types in NYC include detached rear-yard structures (backyard cottages), garage conversions, basement apartments, and additions attached to the main home. The right type for your property depends on your lot size, zoning district, and existing structures.

Short-term rentals in NYC are heavily regulated. Guests or tenants must stay at least 30 days in order to remain compliant with NYC regulations. Most ADU owners use their unit as a long-term rental, which is simpler and more predictable. We recommend consulting with a legal advisor for specifics on your situation.