The City of Yes zoning reform opened the door for Staten Island homeowners to build legal rental units on their property. But knowing the door is open and actually walking through it are two different things. Mayor Zohran Kwame Mamdani announced new financing tools and program resources on March 18, 2026 specifically designed to help homeowners move from interest to action — and Staten Island, with its large stock of single-family homes, stands to benefit more than any other borough.

Here is what is available right now, how the application process works, and what Staten Island homeowners need to know before they start.

What Is an Ancillary Dwelling Unit?

An Ancillary Dwelling Unit — the city official term, though most people say ADU — is a self-contained living space added to an existing one- or two-family home. Under the rules finalized by the Department of Buildings (DOB) in late 2025, there are three types eligible for city approval: basement or cellar apartments, attic apartments in one-family homes, and backyard cottages built on the same lot as the main residence.

These units can be rented to tenants long-term, or used to house family members. They cannot be listed as short-term vacation rentals. Each ADU must meet specific requirements for construction safety, fire protection, flood risk, radon levels, and water sensors — requirements developed jointly by DOB, the NYC Department of Environmental Protection (DEP), and the NYC Department of Health and Mental Hygiene (DOHMH).

Why Staten Island Is the Best-Positioned Borough

Staten Island has the highest proportion of single-family homes of any NYC borough. Large swaths of the South Shore — neighborhoods like Eltingville, Great Kills, Tottenville, and Annadale — consist almost entirely of detached homes on lots with unused basement, garage, or yard space. These are precisely the properties where ADUs are now permitted under City of Yes.

The borough also has a strong tradition of multigenerational living. An ADU can allow an adult child to live independently on the same property as aging parents, or help a homeowner offset mortgage costs by generating rental income. For homeowners who bought years ago at lower prices, converting an underused basement into a legal rental unit is one of the most accessible ways to build additional income without selling or moving.

The Application Process: How It Works

The city began accepting ADU applications on September 30, 2025, through the DOB NOW: Build portal. This is an online filing system where homeowners (or their licensed contractors) submit permit applications for ADU construction or conversion.

One of the most useful new features is the Pre-Approved Plan Library (PAPL). Licensed architects and design professionals have submitted ADU designs that have already been reviewed and approved by DOB. Homeowners can browse these pre-approved designs, select one that fits their property, and move to construction without needing to go through a full custom plan review — significantly shortening the timeline.

The city ADU For You program serves as the public-facing home base for all of this: guidance documents, the Pre-Approved Plan Library, and connections to approved design professionals. Neighborhood Restore HDFC is available to provide guidance and advice to homeowners working through the program.

Flood Risk Is the Key Safety Check

Staten Island residents need to pay particular attention to flood risk requirements before applying. DEP has published an updated interim flood risk area map showing the 10-year rainfall flood risk zone and the coastal flood risk zone. Subgrade ADUs — meaning basement or cellar apartments — are prohibited in areas designated as high flood hazard zones on this map.

Given Staten Island history with coastal flooding, especially in low-lying neighborhoods along the South Shore, this is not a technicality. Homeowners should check the DEP flood risk map before investing in plans for a basement apartment. The DEP map is available at nyc.gov. If your property is in a flood hazard area, a backyard cottage or attic apartment may be a more viable option than a basement conversion.

Legalizing Units That Already Exist

Many Staten Island homeowners already have basement apartments or accessory units that have been occupied without city permits — a common practice across the borough for decades. The city is developing a legalization pathway under Local Law 126, a pilot program that would allow owners of pre-existing basement and cellar apartments to apply for a 10-year temporary authorization while working toward full legalization. Rules for this program are still forthcoming from DOB, but the framework is in place.

This is important: if you already have a tenant in an unpermitted basement unit, the legalization program — when it launches — may allow you to bring that unit up to code without having to evict the tenant or gut the apartment. Watch the DOB website for rule updates.

Additional Support Programs

The city HPD (Housing Preservation and Development) runs the Plus One ADU Pilot Program, which provides additional financial and technical support to homeowners looking to add an ADU. The March 18, 2026 Mamdani administration announcement unveiled expanded tools and financing to help homeowners who want to participate but face upfront cost barriers. Check nyc.gov/site/hpd for current program details and eligibility requirements.

For homeowners navigating NYC housing rules more broadly, our guide to NYC 311 and how to use city services effectively in 2026 is a helpful companion resource. And if you are renting out a unit, understanding tenant rights in NYC in 2026 will help you be a prepared and compliant landlord.

What You Need to Know

• ADU applications for new construction are accepted now through the DOB NOW: Build online portal at nyc.gov/buildings. The application portal opened September 30, 2025.
• Eligible ADU types: basement or cellar apartments, attic apartments in one-family homes, and backyard cottages on the same lot as a one- or two-family home.
• The Pre-Approved Plan Library lets homeowners choose an already-DOB-approved design, skipping most of the custom review process and reducing timelines.
• Basement ADUs are prohibited in designated flood hazard areas — check the DEP interim flood risk map at nyc.gov before making plans for a below-grade unit.
• A legalization pathway for pre-existing unpermitted basement apartments is being developed under Local Law 126. Rules are forthcoming from DOB — watch nyc.gov/buildings for updates.
• HPD Plus One ADU Pilot Program offers additional financial and technical assistance. Visit nyc.gov/site/hpd for eligibility and current program details.
• The ADU For You program (launched by the city) provides online guidance, design resources, and professional referrals. Search “ADU For You NYC” to find the program page.

Sources: NYC Department of Buildings ADU press release; DOB press releases page, March 18, 2026 Mamdani ADU financing announcement.