What is an ADU?

In New York City, an ADU is a self-contained dwelling that’s built on the same zoning lot as another one- or two-family home. Think of an ADU as an extra home, like a rear-yard cottage, a basement unit, or an apartment over a garage. It has its own kitchen, bathroom, and entrance. An ADU is compact, measuring no more than 800 square feet, and is built for residential use only.

What kinds of ADUs can you build in NYC?

New York City allows homeowners to create one ADU per single-family or two-family house. Within that framework, you can choose from several types of ADUs depending on your property and goals. The main options include detached units in the rear yard, attached additions to the main building, and interior conversions such as an attic or basement apartment. Each type has its own design possibilities and requirements in concert with zoning regulations and building construction codes, which are explained in the sections below.

Detached ADU

A Detached ADU is a separate building in the rear yard. This could be a newly built ADU, a conversion of an existing garage into an ADU, or a new ADU constructed above a garage. Detached ADUs offer great privacy and flexibility.

Detached conversion

An existing structure, like a garage or shed, that’s converted or rebuilt into a new living space. Under zoning rules, you can often demolish an existing structure and reconstruct it within the same footprint while still treating it like a conversion.

Detached new construction

A completely new structure built in your rear yard that adds living space where none existed before.

Attached ADU

An Attached ADU is an addition that abuts your building and expands its footprint. It might run beside the main building in the side yard or extend into the rear yard. This is a separate home with its own entrance that either shares a wall with the main building or sits directly beside it, with its own fire-rated wall.

Attached conversion

An existing part of your home, such as a porch, garage, or side addition, that is enclosed or rebuilt to become a separate living unit. The existing space is used to create a legal ADU.

Attached new construction

A new addition built onto your home that creates a separate living space connected to the main structure.

Attic ADU

An Attic ADU uses habitable space under the roof of your home without increasing your property’s footprint. To qualify as a habitable space, the attic must generally provide at least 7 feet of clear ceiling height over a required portion of the floor area, with areas under sloped ceilings counting only where that minimum height is met.

Basement
and Cellar ADUs

A Basement or Cellar ADU is an apartment below the first floor. To qualify as a legal ADU, the basement and cellar must meet safety requirements for ceiling height, light and ventilation, separate access, and fire protection. Basements and cellars have their own requirements for conversion that differ substantially from those of other ADUs.

New Basement and Cellar ADUs

A new Basement or Cellar ADU is built below an existing residence and must meet strict structural, waterproofing, and safety codes. Excavation and foundation work can make this one of the most complex and costly ADU options.

Basement and Cellar conversion ADUs

A basement that is finished or remodeled to create a new, separate living unit within an existing home. The space may already have utilities or partial finishes but requires upgrades to meet ADU safety and code standards.

Simple definitions of basement and cellar

• A basement is a floor that sits partly below grade, which is generally understood as the ground level around your home or the curb level. To be considered a basement, less than half of its height from the finished floor to the ceiling can be below that grade plane.
• A cellar is a floor that sits partly or completely below the grade plane (the level of the ground around your home). To be considered a cellar, more than half of its height, from the finished floor to the ceiling, is below the grade plane.

What is a Rear-Yard ADU in NYC?

A Rear-Yard ADU is a freestanding home (Detached ADU) that sits behind your main building or a home attached to your main building (Attached ADU). Rear-Yard ADUs are known as Backyard Ancillary Dwelling Units in the zoning resolution.

Only some homes in NYC can have a Rear-Yard ADU. The Eligibility Lookup Tool can help determine if you’re eligible to build a Rear-Yard ADU.

If you own a two-family home, adding an ADU may trigger requirements under the New York State Multiple Dwelling Law (MDL). In some cases, you can still move forward by designing the ADU as a fully fire-separated, independent unit.

Because these situations are highly site-specific, it’s best to consult an RDP early in your process. They can confirm what’s possible under your zoning, interpret the code, and help you find the right path to creating a safe and legal ADU.

Why build an ADU?

An ADU is more than an added living space. It’s a way to adapt your home to changing needs, expand opportunities, and invest in the future.

Generate income 

Create an additional rental unit on your property to possibly produce supplemental income.

Live across generations. Bring family closer.

An ADU allows aging parents or adult children to live “next door” while still enjoying privacy.

Age in place. Stay rooted in your community.

A smaller, accessible home on your property lets you downsize while staying at home and in your neighborhood. Explore more about Aging in Place.

Add space and value

An ADU can help make better use of your zoning lot and create flexible space that can adapt to your needs over time. It can also add to your property’s long-term value.

Support gentle growth for your neighborhood

Adding an ADU means adding affordable housing. You provide more choices for people, strengthening both your neighborhood block and the City.

Room labels

Dimensions

Understanding key dimensions can help you understand scale, which is the relationship between the human body and space or another object, and the size of rooms and other design elements.

Doors

The direction of the arc represents the direction of the door swing. 

Wall thickness

Parallel thick lines typically represent exterior or structural walls, while thinner parallel lines represent interior partitions.

Windows

Windows in plans are represented by breaks in the wall. Windows are typically represented by a series of tightly drawn parallel lines.

Furniture and fixtures

Furniture and fixtures (like toilets and sinks) indicate fixture location and demonstrate the scale of what can fit in each space.

What is the process for building your ADU?

Your ADU journey starts here. This is your chance to imagine how your home can grow with you. Through each step, talk with your family, architect or engineer, or the City agencies guiding you toward creating a new legal, livable home. The following outlines your ADU building process, from determining eligibility to occupying it.

Process

1. Check Your Eligibility
2. Determine Your Goals
3. Plan Your ADU
4. Build Your ADU
5. Prepare to Move In

Check your eligibility

Look up your address

Before diving into design ideas, check whether your property is eligible for adding an ADU. In NYC, your eligibility depends on a few factors. Is your home a one- or two-family residence? Does it fall within a flood hazard zone? Use the Eligibility Lookup Tool to find out what is allowed on your lot.

Understand your available square footage

Once you know that you're eligible to build an ADU, the next step is figuring out how much space you can use and checking whether you have already maxed out your buildable zoning floor area. For attic or basement units, the size usually fits within the area of your existing floor.

For Rear-Yard ADUs, zoning rules decide the size of the footprint. Use the Eligibility Lookup Tool to estimate your buildable area. You can also check the NYC Department of Buildings (DOB) rules and regulations page to learn how to calculate the floor area yourself. Don’t forget to verify the dimensions of your rear yard or home.

Determine
your goals

Understand how an ADU can benefit you

Start by thinking about why you want an ADU. Do you need space for a relative, a rental apartment to generate extra income, or a long-term investment? Understanding your goals will help you consider your options. This way, you can make informed choices about size, layout, and budget.

Building in your rear yard

Building an ADU from design to completion can take anywhere from two months to two and a half years. The timeline depends on factors specific to your project, including the design complexity of the ADU you select, property conditions, and permitting, as well as how quickly you make decisions and stay involved throughout the process. It’s best to plan a flexible timeline rather than a firm deadline since unexpected challenges can arise in any site-specific construction project. 

You’ll need to hire a Registered Design Professional (RDP) and a construction team, including specialists like plumbers and electricians, during this phase. You’ll also connect with NYC agencies like the DOB, Department of Environmental Protection (DEP), and Department of Housing, Preservation & Development (HPD). As the project unfolds, you’ll need to monitor progress, coordinate with your design professionals, and consider the best financing options. 

Plan your ADU

Survey your property

Before moving forward with ADU plans, hire a professional New York State–licensed land surveyor or building surveyor to confirm your lot and house sizes and to assess your home’s existing conditions. At a minimum, it is important to obtain accurate information on your property's utilities, easements, contours, and spot elevations. For interior ADUs, it’s important to understand your home’s existing structure and utilities, as well as its overall condition. Assess the strength of the framing, the location of load-bearing walls, and the condition of floors, ceilings, and foundations before beginning to design. 

Choose a pre-approved or custom design

Depending on the type of ADU you plan to build, you may have access to several methods by which to build it. You could use a plan from the City’s Pre-Approved Plan Library (PAPL), or you can choose to work with an RDP to create a custom design. Another option is to buy a manufactured home and have it installed in your rear yard. 

Understand your budget

Your budget will shape when and how you move forward with an ADU. Be sure to account for both short- and long-term costs, including construction expenses and potential increases in property taxes and maintenance. Some income-eligible homeowners may qualify for City- and State-funded programs, such as the Plus One ADU Program, which may provide financial assistance and support with feasibility planning and project management. You can also explore the costs and rewards of building an ADU by using the Budgeting Tool. 

Build your ADU

Choose a Registered Design Professional 

Whether you opt for a preapproved design, a manufactured home, or a custom plan, it’s essential to find an RDP who works well with you and is a good fit for your project. For designs chosen from the PAPL, you’ll work with the approved R DP attached to the design. This guide includes questions to ask your RDP before you sign a contract, and questions that help confirm whether their services align with your ADU goals. 

Contract with a Registered Design Professional 

Once you’ve confirmed that your property is eligible, set your goals, picked a design, and planned your budget, the next step is to hire an RDP, whether a New York State–licensed architect or engineer.  

Get more information and guidance on selecting an RDP on the DOB website. 

Approve and permit your design

After your ADU design is complete, your RDP will submit an application to the DOB for a site-specific review of your approved design. If your building is located in a historic district or is an individual landmark, additional review and approval by the Landmarks Preservation Commission (LPC) is required. Once DOB approves your design, your licensed contractor can apply for and obtain the necessary construction permits. 

If you’re using a design from the PAPL, this application process may be faster and less costly since the plans have already been reviewed and approved by DOB. You will still need approval for your ADU on your specific site. If you’re not using a preapproved design, your RDP will prepare and submit all necessary documents for a full DOB review before permits are issued.  

As the homeowner, you’ll be asked to sign forms authorizing your RDP and contractor to file applications and permits on your behalf.

Construct your ADU

It’s time to start construction. Use the construction timeline to identify key milestones and phases and review the quality assurance cheat sheet to understand what tasks and issues to look out for throughout the process.

Prepare to move in

Conduct inspections 

Once construction is complete, your contractor will schedule a visit with an NYC building inspector to confirm that your ADU is safe and ready for occupancy.  

Learn best practices for being a landlord 

If you build your ADU to rent, remember that being a landlord entails important ongoing responsibilities. Check the “landlord responsibilities” section for an overview and links to City resources that can help both you and your tenants with the process.

ADU Eligibility Lookup Tool 

Use the Eligibility Lookup Tool to see if it is possible to build an ADU on your property. Enter your address to see which ADU types suit your lot. Also, check out the Pre-Approved Plan Library for designs that fit within your property’s allowed boundaries.

Can I build
an ADU?

Your eligibility is based on site-specific regulations, rules, codes, and laws. This includes the New York City Zoning Resolution and Building Code. This chapter outlines the main rules that determine whether your property qualifies, the types of ADUs allowed, and the design limits. If you want to dig deeper, you’ll also find a short guide to zoning and building requirements beyond your lot, plus links to the City’s zoning regulations, building construction codes, and local laws. 

Where are ADUs allowed in NYC?

The map below identifies areas of New York City where Rear-Yard ADUs are allowed and where they are not. This includes historic districts, flood hazard zones, and neighborhoods outside the City’s Greater Transit Zone.

Flood hazard zones  

Basement, Cellar, and Rear-Yard ADUs are not allowed in flood hazard zones identified by the Department of Environmental Protection (DEP). Click the NYC Flood Hazard Mapper to see whether your property is in a flood hazard zone.

Detached conversions, such as a rebuilt or converted garage, may be permitted in flood zones if designed to meet current flood-resistant construction standards. This includes elevating the structure above the Base Flood Elevation (BFE) with additional freeboard to reach the Design Flood Elevation (DFE) as required by Appendix G of the NYC Building Code.

Zoning Regulations (ZRs) and guidelines 

Before you design or build an ADU or contract to purchase and install a manufactured ADU, you need to know the zoning rules that apply to your property. These regulations determine where ADUs are allowed in New York City, how big they can be, and where they can be located on your property. They also set minimum standards for access to light and ventilation, whereas neighborhood context regulations can govern building height, yard space, and separation between buildings. 

This section translates key zoning definitions from ZR Sections 23-341 and 23-371 of the NYC Zoning Resolution into plain language so that you can apply it to your own lot. 

Where on my property can I have an ADU? 

There must be at least 10 feet of separation between the primary house structure and a Detached ADU. The distance helps maintain light, air, and safety between buildings. While larger houses, including those over 35 feet tall, may require greater separation from other residential buildings, the 10-foot minimum applies specifically to ADUs and their primary houses. 

Distance Between New and Existing Structures | ZR Sections 23-341 and 23-371 

How big can my ADU be? 

Your ADU cannot exceed 800 square feet. 

Area | ZR Section12-10 

For ADUs added to a detached, semi-detached, or zero-lot-line building, the height is capped at one story. It can't exceed 15 feet in height, measured to the highest point of the roof. 

Maximum Building Height | ZR Sections 23-341 and 23-371 

If the ADU has a parking space or garage below, it is limited to two stories and cannot go over 25 feet high, measured at the highest point of the roof. 

Maximum Building Height with Garage | ZR Sections 23-341 and 23-371 

A Detached ADU cannot take up more than one-third of your property’s ZR-required rear yard. The rear yard is the open space at the back of your property measured 20 feet into the lot from your rear lot line. For example, to build a 500-square-foot ADU, your rear yard must be at least 1,500 square feet. 

Rear Yard Requirements | ZR Sections 23-341 and 23-371 

What other key zoning regulations should I know? 

Initial Occupancy | ZR Section 12-10

Detached ADUs require a side yard at least 5 feet wide with direct access to the street. This typically rules out row houses with walls attached to neighboring structures on both sides.

ADU Access | ZR Section 12-10

Want more details? Explore related information in the appendix.

Deed restrictions and property conditions  

What are deed restrictions? 

Existing and new restrictions 

Soft Costs

Surveyor
Most projects start with a property survey. This checks lot boundaries, dimensions, and site conditions, helping ensure your ADU design meets zoning rules. It also helps you avoid issues with neighbors. A site topographic and utility survey will be required for NYC Department of Buildings (DOB) and Department of Environmental Protection (DEP) applications.

Registered Design Professional (RDP) fees  
If you hire an RDP, such as an architect or engineer, for a custom design, they will work with you to create an ADU that fits the site of your home. Choosing a pre-approved plan from the Pre-Approved Plan Library (PAPL) can make that process faster and simpler since some design and compliance reviews are already complete.

Engineering fees 
Structural, mechanical, or civil engineers may need to sign off on the design. These services help ensure that the ADU meets construction code requirements. Using a preapproved plan may reduce the need for additional engineering application reviews and help reduce fees.

Insurance for the building process
Construction insurance, also called builder’s risk insurance, covers damage or accidents during construction and protects both your property and your contractor. In most cases, the contractor carries this policy, but some lenders or insurers may require the homeowner to hold it instead. If the contractor provides the policy, your insurer may still require additional coverage on your primary residence during construction. Before construction begins, confirm who is responsible for securing the policy with your RDP, contractor, and insurance provider.

Submetering
Some utilities, particularly water and electricity, may require service upgrades or panel modifications to accommodate separate metering. Coordinate early with utility providers to confirm feasibility and compliance. 

Approval and permitting fees
Every ADU requires a DOB construction permit. Using a preapproved plan can speed up review. Depending on your site, you may also need additional permits from other City agencies, such as the Department of Environmental Protection (DEP) or the Fire Department of New York (FDNY), the Landmarks Preservation Commission (LPC). The general contractor may request the owner to pay the cost the GC will incur for “pulling” the required insurance policies. Regardless, the GC insurance cost will be included in the construction cost.

Property insurance
Once your ADU is complete, you’ll need to update your insurance coverage, either by adjusting your current homeowner’s policy or by obtaining a separate policy for the new unit.

Possible tax increase
Because the ADU raises your property’s assessed tax value, you should plan for a modest increase in annual property taxes.

Testing consultant
Some properties may require professional testing to ensure safety before construction. This can include soil analysis for foundations, structural assessments, or environmental testing for hazards like lead, asbestos, or vapor intrusion in your existing home or garage. If your ADU will be partly or fully below ground, you must conduct radon and vapor testing to meet NYC health and building standards.

Temporary utilities
Contractors may need temporary water or electricity during construction. 

Hard Costs

Building materials
Materials include lumber, roofing, windows, insulation, and finishes. The cost of materials varies depending on quality and market conditions.

General contractor
Your general contractor manages the construction of your ADU from start to finish. They coordinate subcontractors, order materials, and ensure the project meets code and safety standards. Selecting a licensed and insured contractor is essential. Ask for references, check their permit history, and confirm that they are familiar with ADU construction in New York City. The general contractor’s fee is typically a significant part of your overall budget and should include both labor and project management costs.

Equipment rental
Some ADU projects may require specialized equipment for excavation, lifting and moving materials, or the setting of a manufactured unit in place. These costs are included in your contractor’s estimate but can vary depending on the type of ADU and site conditions.

Foundation excavation
Depending on the type of ADU you are building, excavation may be required for the foundation. Existing structures may also need foundation repairs or reinforcement before construction begins.

Utility hookups
Connecting your ADU to City services such as water, sewer, and electricity requires licensed professionals and City approvals. These connections link your new unit to the main lines and should be factored into your hard costs, while permit and inspection fees count as soft costs. Actual expenses depend on the distance to existing service lines and the condition of current connections. 

Mechanical/electrical/plumbing (MEP) labor
Once utilities are in place at your ADU, licensed tradespeople install and connect the interior systems that make it livable. This includes electrical wiring for lighting and outlets, plumbing systems for kitchens and bathrooms, stormwater drainage, and heating and cooling systems that tie into or operate independently of your main home. 

Restoration work
Construction can affect existing site conditions such as yards, plantings, driveways, and sidewalks. Once the main work is complete, you may need to restore landscaping, repair the driveway and/or sidewalk pavement, or regrade soil for proper drainage. A new Rear-Yard ADU may trigger the requirement for a Builder’s Pavement Permit, front-yard planting, and a street tree requirement per zoning.

Demolition 
If you’re converting or rebuilding an existing structure, such as a garage or shed, partial or full demolition may be required before construction can begin. In New York City, demolition is regulated by the DOB, the DEP, and the FDNY. Each agency may require permits or inspections to address air quality, asbestos removal, and fire safety. Full demolitions require a building permit. Always confirm which approvals apply to your project before starting any demolition work.

Site work 
All exterior ADUs require site preparation before construction. This may include grading soil for drainage; pouring concrete for new foundations, such as footings; and installing walkways or retaining walls. For Basement, Cellar, or Attic ADUs, site work might involve improving exterior access routes or adding new stairs. Proper site work ensures the new ADU integrates safely and smoothly with your existing property.

Sprinklers
ADUs in New York City are required to have a sprinkler system. There are specific requirements for basement and cellar apartment units. Installation must be performed by NYC-licensed professionals and approved by DOB inspections. 

Attic work
If you’re planning on converting your attic into an ADU, it’s important to keep in mind that your roof may require replacement or repair. Bringing an Attic ADU up to code also requires proper insulation that meets New York City’s energy standards. Explore information related to insulation standards.

How can I finance my ADU?

Adding an ADU is a major investment, but homeowners have several ways to finance it.

Conventional financing options include:

Home equity loans

This type of loan lets you borrow money based on how much of your home you already own. You receive the money to design and build your ADU all at once and pay it back in fixed monthly payments like a second mortgage.

Home equity lines of credit (HELOC)

A HELOC gives you access to a flexible line of credit that you can draw from as needed during your project. It uses your home's value as security. You can withdraw money as needed during your project and pay interest only on what you use.

Construction loans

A construction loan provides short-term financing to cover building costs while your ADU is under construction. Once the project is complete, it often converts into a standard mortgage or long-term loan.

Cash-out refinancing

With a cash-out refinance, you replace your current mortgage with a new one that’s bigger. You get the difference in cash, which you can use to pay for your ADU, but you’ll start a new mortgage in the process.

Personal loans

A personal loan gives you money up front without requiring you to use your home as collateral. It may be faster to get, but it may come with higher interest rates and shorter repayment terms.

These options are widely available through banks and credit unions and can be paired with City and State programs designed specifically for ADU development.

The Plus One ADU Program

The City’s flagship financing tool is the Plus One ADU Program, which combines capital loans and grants to help eligible homeowners build or legalize ADUs.

Key features include:

• Additional construction loan financing through Housing, Preservation & Development (HPD)
• Loan terms of up to 15 years, with potential extensions to 30 years
• Interest rates as low as 0% for eligible borrowers
• Preference for owner-occupants earning up to 120% of area median income (AMI), with eligibility extending to 165% AMI
• Forgivable loan options tied to rent restrictions and capped annual rent increases, depending on the loan structure
• Monthly payment safeguards that ensure homeowners retain at least $200 in monthly cash flow after debts

To qualify, homeowners must occupy their homes, be current on mortgage payments, and have no outstanding municipal arrears.

Calculating potential rental income 

Financing an ADU often involves balancing construction and ongoing maintenance costs with future rental income. You can estimate rental potential by comparing local market rents to projected monthly loan payments, factoring in insurance, maintenance, and utility costs. Our Budgeting Tool helps model these scenarios so you can understand when and how your ADU can begin to pay for itself. 

City incentives  

New York City offers a variety of programs to support you when your ADU project contributes to sustainability, housing growth, and/or first-time rental opportunities. These programs provide financial incentives, tax benefits, and technical assistance that can help offset costs and facilitate the process of becoming a landlord.

NYC Accelerator
Free expert guidance, training, and resources to help building owners     improve energy efficiency and comply with local energy laws. It connects homeowners with rebates and financing opportunities.

NYSERDA incentives
Programs that support multifamily retrofits and renewable energy, solar, and electrification projects, with options for affordable housing and smaller properties.

Plus One ADU Program
Grants and financial support for homeowners creating ADUs are available,     especially for those becoming landlords for the first time.

Steering clear of predatory lending

Lenders can open the door to financing your ADU, but they may not always have your best interests in mind. Predatory loans often come with unfair terms, hidden fees, or interest rates that make repayment nearly impossible. Some red flags include high-pressure sales tactics, promises of “guaranteed approval,” loan terms you don’t fully understand, or being asked to sign blank documents.

To protect yourself, always compare offers from multiple lenders, read the fine print carefully, and ask questions until you’re comfortable with every term. Working with reputable banks, credit unions, or City-endorsed financing partners is the safest route. If something feels off, like payments that don’t add up or fees that weren’t disclosed, don’t sign. A good loan should be transparent, predictable, and affordable over the long run.

Homeowner Help Desk

The Homeowner Help Desk (HHD) provides free support to low- and middle-income homeowners across New York City. Scammers often target households facing financial strain, but HHD connects you with trusted housing counselors and legal experts who can help you protect your home and your future. They may also help guide you through your ADU costs and loan process.

The Homeowner Help Desk may assist you with: 

• Preventing foreclosure and managing mortgage payments
• Protecting against scams, deed theft, and predatory lending
• Resolving property tax and water bill debt
• Applying for low-cost loans and home repair resources
• Improving energy efficiency and accessing upgrade programs
• Creating an estate plan to keep your home in the family
• Understanding flood risks and insurance options
• Managing your home as a small landlord

For neighbors and family 

You don’t need to be a homeowner yourself to make a difference. HPD offers workshops and training to help you recognize the signs of scams and deed theft so you can support friends, family, and neighbors.

Contact information 

If you’re a homeowner in need of support, call (646) 786-0888 or visit homeownerhelpny.org. Assistance is free and confidential.

Renting out your ADU

You may have built your ADU with the goal of renting it. In New York City, rental rules depend on whether you plan to offer the apartment for a short-term stay (fewer than 30 days) or a long-term lease (30 days or more). Understanding the difference is key to staying compliant and protecting yourself as a landlord.

Short-term rentals (fewer than 30 days) 
You can’t use your ADU as a short-term rental unless you live in the ADU as your primary home while hosting guests. New York City’s Local Law 18 requires all short-term rental hosts to register with the Mayor’s Office of Special Enforcement and to follow safety and occupancy rules.

Violating these rules can lead to significant fines. 

Helpful resources:
Final Rules Governing Short-Term Rentals (NYC.gov)
Local Law 18 of 2022 (Full Text, NYC.gov)

Long-term rentals (30 days or more)
If you rent your ADU to a tenant for more than 30 days, it falls under New York City and New York State landlord-tenant laws. These laws cover leases, rent regulations, eviction processes, and the basic rights and obligations of landlords and tenants. As a homeowner, you’ll need to follow rules around habitability, security deposits, and notice periods.

Helpful resources:
NYC Tenants’ Rights Guide (NYC.gov)

Residential Tenants’ Rights Guide (New York State Attorney General)

Changes in New York State Rent Law

2025 Apartment/Loft Rent Guidelines Board Order

NYC Department of Housing Development & Preservation ABCs of Housing

What type of ADU is best for your property?

The New York City Zoning Resolution determines which ADU types you can build and where, but your goals and resources as the homeowner will guide which options make the most sense for you. Each type offers different advantages depending on how you plan to use the space and who will live there. The examples below can help you analyze what fits your needs and assist you through the ADU design process.

Detached ADU

A Detached ADU is a separate building in the rear yard. It can be a new building, the conversion of an existing garage, or another type of outbuilding. Detached ADUs provide the greatest level of separation, privacy, and flexibility.

Consider a Detached ADU if:

• You want to create an independent rental unit that offers privacy for both you and your tenant. The separation between homes can make the unit more marketable and potentially increase its rental value.
• You want to create an intergenerational household while maintaining a degree of separation and privacy.
• You want to age in place. Detached ADUs can be designed to meet accessibility and mobility needs, allowing aging adults to downsize while staying in their neighborhoods.
• You want a straightforward permitting-and-design process by selecting an ADU from the Pre-Approved Plan Library.
• You have a garage or rear-yard structure that can be rebuilt or adapted into a new living unit.
• You want to build an ADU but would prefer to avoid triggering the Multiple Dwelling Law by adding an ADU to an existing two-family home.

Rear-Yard ADU (new construction)

A Rear-Yard ADU is a newly built home located behind the main building. It must meet zoning requirements for setbacks, height, and distance from the main house. This option gives you design flexibility and allows for a fully customized layout but will typically cost more than a conversion.

Detached ADU conversion (garage or outbuilding)

A Detached ADU conversion repurposes an existing structure, like a garage, into a livable home. Conversions can be more affordable, but they often require upgrades for insulation, foundation, structure, and utilities. Some garages may need partial demolition or rebuilding to meet current codes.

Attached ADU

An Attached, or Abutting, ADU is a new unit physically connected to your main house. It may extend along the side of the home, project into the rear yard, or be created by converting an existing enclosed space, such as a sunroom or porch. Although it connects to the primary structure, it must function as an independent dwelling and include a fire-rated wall that fully separates the new living space from the main home, as required by code. This type of ADU does not increase the building footprint unless a new floor area is added.

Consider an Attached ADU if:

• You are seeking to generate additional income through a long-term renter in a building that abuts your own, depending on your home’s classification and fire separation requirements.
• You are looking to foster an intergenerational household for either aging parents or an adult child by creating a new living space that’s attached to the main building.
• You want to maintain a shared yard or access while still offering a private entrance and living area.

Attic, Basement, and Cellar ADUs

An Attic ADU uses space under the roof without increasing your property's footprint. A Basement or Cellar ADU is located below the main floor.

Consider an Attic, Basement, or Cellar ADU if:

• You are seeking to generate additional income through a long-term renter by utilizing the existing structure of your home.
• You are looking for more seamless integration into your existing structure. Attic, Basement, and Cellar ADUs may be more discreet because they aren’t new external structures. 
• You have limited space in your rear yard for an additional structure.
• You are looking for more seamless integration into your existing structure.

What ADU features are best for your goals?

Once you know which ADU type fits your property, vision, and goals, you can start thinking about design features that matter most to you. Common goals when creating an ADU include accessibility, parking, sustainability, and comfort. We recommend talking with your RDP or looking for these features in the PAPL design descriptions.

Accessibility and universal design

Check out the NYC Department of Aging's Aging in Place Guide for Building Owners for more ideas.

• No step/ground level with wide entries
• Walk-in showers
• Elevator or stair lift
• Assistive railings or handrails
• Wheelchair turning radius

Preserve parking

• Two-story garage conversion
• Covered parking space integration
• Electric vehicle (EV) charging

Sustainable systems

• High-performance insulation and windows
• Solar panels for electricity production
• Green roof
• Rainwater harvesting
• All-electric appliances

Comfort and livability

• Skylights, dormers, or roof windows
• Outdoor patio or porch
• Soundproofing

What is the Pre-Approved Plan Library? How can you use it?

The Pre-Approved Plan Library (PAPL) is an online resource where you can explore Detached and Attached ADU designs created by licensed professionals. Each design has been reviewed and approved by the NYC Department of Buildings (DOB), which may help speed up the early approval and permitting process for your specific site. When you choose a design from the PAPL you must enter into a contract with the RDP who created it. Even if you don’t elect to use a PAPL ADU design, the PAPL is a good resource of ideas for what the interior and exterior of an ADU can look like.

Working with a Manufactured ADU

Factory-manufactured housing, also known as prefabricated, follows different U.S. Department of Housing and Urban Development (HUD) codes and regulations than homes built directly on-site in New York City. Many homeowners find this option appealing because it can significantly shorten the construction timeline and lower overall costs.

Manufactured homes certified by New York State or HUD can be used as ADUs if they meet the requirements of NYC Building Code Appendix U. Although these homes are regulated by state and federal governments, the City reviews zoning, site placement, and connections such as utilities and foundations to ensure compliance with local requirements.i1ii If you’re unsure whether a specific manufactured home qualifies, contact the company or RDP associated with the design to confirm compliance.

Where to
start with a
custom plan

You may need to consider designing a custom plan for your ADU for the following reasons:

1. Interior ADUs, such as Basement, Cellar, and Attic ADUs, are not included in the PAPL and require custom plans due to the unique building features of each one- and two-family home.
2. The Pre-Approved Plan Library does not include a design option that meets your vision or needs.

If your project requires a custom plan, start the process by researching and contacting an RDP. An RDP is a New York State–licensed architect or engineer who will design your ADU, prepare the necessary drawings, and ensure that your project meets all NYC Construction Code and Zoning Resolution requirements. The RDP is also responsible for signing and stamping your permit application drawings.

When selecting an RDP, you should check both disciplinary and licensure records to ensure you're working with a qualified and reputable professional. You can search RDPs to verify their licenses and review their professional histories by using the NYS Education Department’s Verification Search.

Before meeting with an RDP, it may be helpful to:

• Secure a recent property survey.
• Evaluate your goals for building an ADU (for example: generating rental income, housing a family member).
• Determine a general budget range.
• Refer to the “Selecting your Design Professional” section for a list of questions to ask while interviewing your RDP.

The RDP will usually visit your site, manage the project, and create design drawings that reflect your goals. They also prepare the documents needed for filing with the Department of Buildings so your project can move forward with construction permits.

An architectural plan is a drawing that shows a bird’s-eye view of a building or a space as if a horizontal slice were cut through it. For your ADU, it illustrates how rooms, walls, doors, and fixtures are arranged. Learning how to read a plan helps you communicate with your RDP and contractor so you can make confident, informed decisions about your design. The diagram below highlights some key elements to look for in an architectural plan.

Selecting your Registered Design Professional

Choosing an RDP, whether a New York State–licensed architect or engineer, is one of the most important decisions you make. A skilled RDP will listen carefully, design creatively, and help you meet City regulations without surprises.

How to
choose well:

Verify Credentials

Use the Find Licensed Professionals tool to confirm that your RDP’s license is current and check for disciplinary actions.

Ask for experience

Look for someone who has worked on ADUs, small residential additions, or residential conversions in NYC.

Review past work

Ask to see similar projects. You want to understand how they handle space, light, materials, and construction details.

Check references

Call previous clients; they can reveal how the RDP communicates and whether they stay on schedule.

Meet before signing

Bring a property survey and discuss your goals, budget, and timeline.

Questions to
ask during
your meeting:

• Have you designed ADUs, residential rehabs, renovations, or home additions in NYC?
• How do you handle DOB filings and approvals?
• What services are included in your proposal?
• How do you estimate costs and manage revisions?
• What does your timeline from design to permit look like?
• How do you usually respond to delays in a project?
• What have you done previously when a project is delayed past when you expected?
• How often do you typically communicate with homeowners, and about what aspects of the project?
• How much do you participate during the construction of a project?

Every homeowner should have an ADU checklist

All ADUs are required to include specific elements to be legally compliant and habitable. These requirements include:

Kitchen

• The ADU must include a space for preparing meals, including a stove, sink, and counter.
• It must meet all plumbing and ventilation requirements as set by the NYC Construction Codes.

Bathroom

• A complete bathroom, including a toilet, sink, and shower or bathtub, must be present. The ADU must have an appropriate venting system and plumbing that connects to the sanitary sewer. The bathroom cannot be directly connected to the kitchen.

Separate designated entry

• This entry must be separate from the entrance to any other existing units and cannot be more than 100 feet from your property’s street line.

Bedroom or sleeping space with operable windows

• A sleeping space must have adequate natural light and ventilation. In basements and cellars, all rooms must have a window large enough for escape during emergencies and provide two means of egress.
• The window must meet minimum size, opening, and sill-height requirements as defined in the NYC Building Code.

Connections to utility networks such as electricity and plumbing

• The ADU must be properly permitted and connected to the local utility networks: electrical, water supply, sewer, and, where applicable, HVAC systems.
• Every plumbing fixture (kitchen sink, bathroom sink, shower/tub, etc.) must have both hot and cold water as required by health, safety, and code standards.
• Water heaters, distribution, insulation, and pipe sizing must comply with code.
• Almost all ADUs must include a sprinkler system. The requirements change between Detached, Attached, Attic, Basement, and Cellar ADUs. A single-family home plus an Abutting ADU does not require a sprinkler system.

Understanding Multiple Dwelling Law and costs

If you already have multiple units on your property or plan to add more with your ADU, your project may fall under New York State’s Multiple Dwelling Law (MDL). Two-family homes that add a firewall-separated Attached or Detached ADU are exempt, but adding units beyond this can trigger additional building code requirements. These may include upgrades to fire separation, sprinklers, and egress, which can add to your project’s overall cost. Check with your RDP early to understand whether MDL applies to you.

Common misconceptions about ADUs

It’s important to know that not every extra structure or space on a property can qualify as a legal ADU. Sheds, treehouses, or unregulated basement and cellar apartments may seem similar but usually don’t meet the standards required for safe, habitable housing under NYC regulations. Informal basement and cellar apartments, for example, may be illegal and must be upgraded to meet all building and zoning requirements, including proper exits, natural light and ventilation, plumbing, and electrical systems, before they can be considered legal ADUs.

Environmental impacts of ADUs

New York City needs more housing, but certain materials and designs can impact the building’s carbon footprint during construction and over the long term. As a homeowner, you can make choices that reduce these impacts. Thoughtful decisions about energy use, insulation, and building materials can make your ADU more sustainable and contribute to a healthier City.

The diagram below highlights opportunities to reduce your ADU's carbon footprint.

Help minimize energy loss

• Increase building energy performance. Ask your RDP to increase your window and wall insulation performance beyond the required standards.
• Use fewer windows! Windows allow for higher energy loss than walls. Talk to your architect about how to make your home light-filled and airy without using floor-to-ceiling windows.
• Consider all-electric systems. Electric heat pumps and induction stoves can reduce your home’s carbon footprint and improve indoor air quality but may increase upfront electrical costs. Discuss whether your existing electrical panel and service can support full electrification. Rear-Yard ADUs are considered new builds and are covered by LL 2022-154. Currently, they need to be all electric except for hot water, which will be required to be electric in 2027.
• Choose efficient appliances and fixtures. Look for ENERGY STAR®-rated appliances and WaterSense®-certified, low-flow fixtures to reduce energy and water use over time.
• Properly orient your ADU. Talk to your RDP about which direction your property should face to get the best sun (and heat) in the winter and summer.

Manage water on-site

• Some ADUs may have an opportunity to collect and manage stormwater and graywater. Stormwater management is required by NYC DEP when an ADU creates more than 200 square feet of impervious area. Talk to your RDP if you are interested in water management.

Choose less environmentally intensive building material

• Choose lower-impact structures. Typically, structures made of wood have a lower negative environmental impact than buildings made from concrete or steel.
• Use local or regional materials. Ask your RDP to source materials that are within 500 miles of your home or closer.
• Use lower-impact materials. Depending on the materials of your building, you can ask your RDP to work with locally sourced materials, low-carbon concrete, wood from a sustainable forest, recycled steel, or steel from electric arc furnaces.

Choose low-impact finishes

• Work with your RDP to choose finishes that are healthy for your body and the environment. Materials like vinyl are slow to decompose and require significant processing of energy. Ask about known health outcomes, such as off-gassing of noxious odors, associated with highly processed materials.

Save trees
when possible

• Whenever it’s an option, you should attempt to save existing trees on your property. If you must remove a tree, consider planting a new one or contributing to a City initiative such as the NYC Urban Forest Plan.

Environmental certifications

• Ask your RDP if the design is compatible with LEED v4.1 Residential: Single Family Certification, Passive House Design, Zero Energy Ready Home (ZERH), or ENERGY STAR standards.

Take advantage of opportunities to upgrade your existing home

• Consider investing in your property to reduce the environmental impact of your existing home. Price out options to replace your windows, improve roof insulation, improve your utility efficiency, or install photovoltaic panels.

Permitting plans 

What is the ADU permitting process in NYC?

Every ADU project in New York City requires a building permit from the Department of Buildings (DOB) before construction begins. Your RDP, whether a licensed architect or engineer, will handle the filing process, coordinate reviews, and ensure your design complies with zoning and construction codes. 

Understanding permit types 

Most ADU projects use one of two permit categories filed through DOB NOW: Build: 

• New Building (NB): Used when you are constructing a new Detached ADU on your property. This includes demolishing an existing accessory structure, such as a garage or shed, and rebuilding a new Detached ADU in its place. 
• ALT CO (formerly ALT1): Covers major changes that affect the building’s use, egress, or occupancy (for example, converting a two-family house to a three-family house) and changes that require a Certificate of Occupancy (CO) or the revision of the existing CO. Demolition and reconstruction that do not create a new, freestanding building but instead modify the existing building are typically filed under this category. 

Your RDP will advise which category applies and will prepare the required permit application documents and drawings. A DOB plan examiner will then review the submission for compliance. If there are objections, your RDP will respond with corrections until the permit application is approved. Learn how to obtain a permit on the NYC DOB NOW page. 

Explore how to use DOB NOW.

With a preapproved plan 

If you use a design from our Pre-Approved Plan Library, your RDP may be able to adapt the design to your site’s dimensions and submit it directly to DOB. These plans have already cleared key technical reviews, so approvals may move faster.

Follow these steps when using the Pre-Approved Plan Library: 

1. Confirm eligibility with your RDP. 
2. Select the plan that fits your goals, resources, and lot type. 
3. File through DOB NOW: Build as a New Building or Alt-CO-GC job (“GC” here means “general construction”), including the Pre-Approved ADU Plan Number. 
4. Receive DOB application approval so the contractor can pull the permits. 

Without a preapproved plan 

If your project requires a custom design, common for Attic, Basement, Cellar, or even Rear-Yard ADUs, your RDP will prepare all drawings and technical documents from scratch.

Follow these steps if you’re not using a design from the Pre-Approved Plan Library: 

1. The RDP designs the ADU and confirms that it meets zoning and construction code requirements, such as structure and fire-safety design requirements. 
2. The application with its plans is filed for DOB review and correction, if needed. 
3. After application approval, your general contractor can pull the building permit. 

Next steps 

Once permits are issued, construction can begin. The completed ADUs must be inspected and approved and obtain a Certificate of Occupancy or Letter of Completion before anyone can move in. 

Attic, Basement, and Cellar ADUs

Attic ADUs must meet requirements for ceiling height, egress, fire separation, insulation, ventilation, and natural light. Your RDP files the project as an ALT-CO or New Building job, depending on whether it is within an existing home. 

Basement ADUs can be created in one- or two-family homes if they meet Building Code and zoning requirements for safety, moisture control, flood risk, and adequate light and air. Your RDP can confirm whether your basement meets the conditions for a legal conversion.

Learn how to obtain a permit and explore the Project Guidelines for Owners. You can also contact a NYC DOB Project Advocate located in the DOB borough office where you live for support with the process. 

Asbestos requirements

If your home was built before 1987, you must complete an asbestos assessment before the DOB will issue a construction permit. This ensures that no asbestos containing materials (ACM) will be disturbed during construction. If asbestos is to be removed, the NYC Department of Environmental Protection (DEP) will require permits to do so. Explore the details on the DEP asbestos abatement page. 

Legal responsibilities

License and access agreements 

In New York City, building close to another property often means you’ll need your neighbor’s cooperation. When ADU construction on your lot requires access to an adjoining lot, whether to install scaffolding; protect a shared wall, party wall, or retaining wall; or underpin a foundation, you’ll need a written agreement licensing access to your neighbor’s property. These documents formalize permission, outline conditions, and protect everyone involved.

Because these agreements are legal documents, you should work with your RDP and an attorney to draft or review them. Your RDP can identify when an access agreement is required based on your site conditions and construction scope, and an attorney can ensure the terms protect your access rights and your neighbor's property. 

What access agreements cover 

A clear and complete access agreement removes ambiguity. It plainly defines what you need to do on your neighbor’s property, what you are allowed to do, how long you can do it, and how you’ll protect your neighbor’s property. Typical provisions include: 

• Description of permitted work that explains what activities are allowed, such as excavation, façade protection, or repairs 
• Scope of access detailing which individuals or contractors may enter, what type of work they are allowed to do, what areas can be accessed, and what equipment can be used 
• Duration of license specifying start and end dates for property access, plus any extensions or termination clauses 
• Compensation for inconvenience paid to your neighbor, often ranging from a few hundred to several thousand dollars per month, depending on risk and duration 
• Insurance and indemnification to protect both parties from damages and/or liability

The legal framework: RPAPL § 881

When voluntary agreements can’t be reached, New York’s Real Property Actions and Proceedings Law § 881 provides a formal path. RPAPL § 881 is a New York law that allows a property owner to petition the court for a license to enter an adjacent property to make necessary improvements or repairs that cannot be done otherwise. 
 

This law allows you and your neighbor the chance to petition the court for access when it’s necessary for improvements or repairs. The court balances the interests of both sides and, if access is granted, sets fair conditions of a license, such as compensation and insurance coverage.

Refusing reasonable access can have consequences. If your neighbor denies entry and a court grants an access license under RPAPL § 881, continuing to block access could result in legal penalties or liability for project delays or for physical or financial damages. The key is communication—your rights and your neighbor’s rights must be understood and respected. 

Limitations and responsibilities

A license agreement only covers what is written. If access is granted for repair work, it can’t be used for new construction without written consent. Access can’t be transferred to another party, and it ends once the permitted work is complete. Any violation—such as staying beyond the agreed period or causing unnecessary disruption—can expose you to legal claims. 

Because these agreements are so specific, it’s wise to start negotiations early, ideally six months before work begins, and work closely with your RDP and/or an attorney experienced in construction law. 

Construction timeline

As a homeowner, you can typically expect the construction of your ADU to undergo seven major phases, from demolition and site preparation to move-in.

1. Demolition/site preparation
2. Foundation
3. Framing
4. Mechanical, electrical, and plumbing (MEP)
5. Drywall and insulation
6. Exterior fit-out
7. Interior fit-out, finishing touches, and inspections

Demolition/site preparation

Foundation

Framing

Mechanical, electrical, and plumbing (MEP)

Drywall and insulation

Exterior fit-out

Interior fit-out, finishing touches, and inspections

Now, finish materials such as flooring, appliances, fixtures, and cabinetry will be installed inside your ADU. Think of this step as the final stretch before move-in. Your RDP can offer guidance on the selection of these materials to ensure they meet building and energy code standards.

Inspections

Common inspections include: 

• DOB inspections for structure, plumbing, electrical, and fire safety
• Utility inspections for water, gas, and electrical connections when applicable
• Special inspections by third-party professionals for items such as energy code compliance, sprinkler systems, or foundation work
• Final DOB inspection to close out all open permits and verify compliance with approved plans

What to look for as a homeowner during construction

It is important to maintain an ongoing dialogue with your selected contractor and RDP throughout the design-and-construction process. The construction process can often feel long, so it is important to remain patient and understand and anticipate potential impacts on your daily life and routine.

Questions and conversation starters to consider as a homeowner:

Schedule and timeline

• When will construction begin?
• When is it anticipated to end?
• What time can I expect workers on-site to work on a day-to-day basis?
• Are there times I should be away from home? What times should I be present?
• What do I do if construction stops?

Safety and construction practices on-site

• How and where will materials, tools, and equipment be stored after the workday?
• What measures will the contractor team take to protect my existing property and possessions?
• Will heavy machinery be needed for my project? If so, when can I expect it to be on-site?
• If construction is done within the existing home, what measures will be taken to keep dust and debris out of occupied areas?

Points of contact

• Who is my RDP point of contact?
• Who is my general contractor point of contact?

Quality assurance and legal matters

• Under what circumstances should I contact a lawyer or pursue legal counsel?
• How will I know if my project has been mismanaged? Whom do I call if I think it's being mismanaged?

Preparing a unit for occupancy

Legal occupancy

After construction is complete and before anyone moves in, you must confirm that your ADU is legal to occupy. Every new building in NYC needs a Certificate of Occupancy (CO), which officially states how the space can be used for the designed purpose and who can live there. Interior and attached ADUs will also require an updated or amended CO for the existing home before they can be legally occupied. To help with the process, you can choose to hire a filing representative, also known as an “expeditor,” who can assist with submitting paperwork and tracking approvals through the Department of Buildings. Your Registered Design Professional (RDP) remains responsible for preparing and certifying drawings, managing technical filings, and completing the steps for your CO requirements on DOB NOW: Inspections.

Documents that should be on hand during the inspection include:

• Approved construction plans, which must always be on-site during construction, as well as sign-off inspections
• Building permits
• Previous inspection reports
• Any correspondence with the DOB

If the inspector identifies any violations, they must be addressed, and a reinspection may be required. Learn about CO requirements at Certificate of Occupancy - Buildings.

What resources are there for
new landlords?

Deciding what to charge for rent

The location of your apartment, its size, and its amenities will determine how much you can reasonably charge in rent while maintaining tenants. One way to start determining how much to charge for rent is to look up similar-sized apartments in your area, also known as comps, and see how much rent is for those units. You can use the Budgeting Tool to compare different rental income amounts to see what works for your budget.

Rent increases

According to New York Real Property Law Section 226-C, landlords in New York must provide tenants with advance notice of a rent increase of 5% or more, with a notice period of 30 to 90 days, depending on the length of the tenancy or lease term.

Broker fees

On June 11, 2025, the Fairness in Apartment Rental Expenses (FARE) Act took effect in New York City. This law prohibits brokers who represent landlords from charging tenants broker fees. Landlords or their agents must disclose other fees that tenants must pay in their listings and rental agreements.

Choosing your tenant and managing the relationship

Screening may include:

• Credit checks
• Work and landlord references
• Personal references
• Questions about the number of people who will live in the unit
• Home visits
• Interviews

After renting your ADU

Landlord responsibilities in NYC

Get support
as a landlord

To see a full list of resources, check out HPD Resources for Landlords and Property Owners.

Ancillary Dwelling Unit

In New York City, an ADU is a self-contained home that’s built on the same lot as another house. Think of it as an extra living space, like a rear-yard cottage, a converted basement, or a garage apartment. Each ADU is a separate home. It has its own kitchen, bathroom, and entrance. An ADU is compact, measuring no more than 800 square feet, and is intended for residential use only.

attached (building)

A building shall be considered attached when it abuts two lot lines other than a street line, or another building or buildings other than a semi-detached building.

Attached ADU

An Attached ADU is an addition that abuts to and expands the footprint of your house. It might run beside the main building in the side yard or extend into the rear yard. This is a separate home with its own entrance that either shares a wall with the main building or sits directly beside it with its own fire-rated wall.

Attic ADU

An Attic ADU is an apartment built within your attic that has enough headroom. It uses space under the roof without changing the footprint of your property. Attic ADUs specifically require automatic sprinklers.

Basement or Cellar ADU

A Basement or Cellar ADU is an apartment located below the first floor of a home. To qualify as a legal ADU, the space must meet specific safety and habitability requirements, including minimum ceiling height, adequate light and ventilation, fire separation, and a legal means of entry and exit. Basements and cellars are defined differently under the Building Code and have distinct rules related to floor level, window placement, and allowable living space; these rules affect whether an ADU can be built in each location.

Building Code

The Building Code is a set of rules and regulations that govern the design, construction, and maintenance of buildings with the goal of ensuring the health, safety, and welfare of building occupants.

building envelope

The building envelope is defined by the enclosure that separates the conditioned space from the exterior space.

building footprint

The building footprint is defined by the area your structure takes up on the ground plane.

Detached ADU

A Detached ADU is a separate building in the rear yard. This could be a newly built ADU, a conversion of an existing garage into an ADU, or a new ADU constructed above a garage. Detached ADUs offer great privacy and flexibility.

detached (building)

A detached building is a building surrounded by yards or other open areas on the same zoning lot.

Dwelling Unit

A single unit providing complete independent living facilities for one or more persons, including permanent provisions for living, sleeping, eating, cooking, and sanitation.

flood zone

A flood zone is a geographic area characterized by its risk of flooding. In New York City, flood zones are composed of two component areas: the coastal flood risk area and the 10-year rainfall flood risk area.

floor area ratio (FAR)

A zoning regulation and formula that determines how many square feet are allowed to be developed on a given property. The FAR is the total floor area on a zoning lot divided by the lot area of that zoning lot.

Greater Transit Zone

The Greater Transit Zone boundaries are used for several zoning rules. They determine where special rules for Qualifying Residential Sites are applicable and how nonresidential parking is calculated in some zoning districts. Being located within the Greater Transit Zone may allow for more or different development opportunities.

gross floor area

Gross floor area includes the total square footage of a built structure. This includes all floors and space taken up by walls, ducts, and stairwells.

lot line

A lot line is a boundary that divides one property from another, or from a street or any public space.

Neighbor Notification Affidavit

A notice provided to adjacent property owners that you plan to apply for and build an ADU on your property.

NYC rulemaking process

New York City creates legally binding rules using a public process called CAPA (City Administrative Procedure Act). First, an agency drafts a rule and posts it for public review. People can share comments online or during a hearing. The agency must consider this feedback before publishing the final rule. This process sets rules on where ADUs can be built. It also outlines safety standards and explains how homeowners can get approval.

City agencies like the Department of Environmental Protection and the Department of Buildings have passed rules. These rules help regulate and ensure quality in the ADU process. You can read more about these rules on the NYC Rules website.

permitting

Building permits are required before construction projects can begin in New York City. Permit applications must be submitted to the Department of Buildings for code compliance review and approval.

Pre-Approved Plan Library

The Pre-Approved Plan Library (PAPL) is a design resource library where you can browse pre-designed Detached and Attached ADUs from industry professionals. The ADU designs in the PAPL have been preapproved by the NYC Department of Buildings, allowing you to fast-track the permitting, approval, and design process associated with building an ADU.

rear yard

The rear yard is the open space at the back of your property measured 20 feet from your rear lot line. In some cases, the rear yard is measured 30 feet from your rear lot line depending on the height of the primary building or lot size.

Rear-Yard ADU

A Rear-Yard ADU is a freestanding home (Detached ADU) that sits behind your main building or a home attached to your main building (Attached ADU).

semi-detached (building)

A building in which the primary dwelling unit abuts another one-family home (think duplex).

setback

A setback is the required distance a building must be offset from an existing building, property line, or street. Setbacks help provide adequate light and air to surrounding streets and open spaces. They also improve fire safety through increased spacing between building structures.

single-family residence

A single-family residence is a building containing only one dwelling unit and occupied by only one family. A single-family residence may also include an ancillary dwelling unit in the same structure or in an ancillary building, if it qualifies.

two-family residence

A two-family residence is a building containing not more than two dwelling units and occupied by only two families. A two-family residence may also include an ancillary dwelling unit in the same structure or in an ancillary building.

zero lot line (building)

A building in which one side is built directly on a property’s lot line, with no side yard on that side.

zoning amendment

Zoning text and map amendments and zoning amendments, whether citywide or area-specific, adjust the Zoning Resolution or map to accommodate developments that align with City planning goals. Amendments are either text-based (changing the Zoning Resolution) or map-based (changing zoning designations). These changes affect all properties equally within the modified area.

zoning district

Each zoning lot has an underlaying zoning district based on the context of the lot in the City. Zoning districts are most commonly differentiated by residential, commercial, and manufacturing uses.

Zoning Resolution

The Zoning Resolution is the law for building and development in New York City. Zoning is how a city splits land into zones. Each zone has its own uses and rules that must be followed. These rules regulate features such as the shape, size, and placement of buildings.

In New York City, a maximum of one ADU is allowed on a property designated as a single- or two-family home. Each single- or two-family home lies within a unique zoning lot. The characteristics of the lot are used to determine if and where you can build an ADU on your property.

1. Core building code framework for ADUs

Beyond zoning regulations, the NYC Building Construction Codes set specific safety and habitability standards that every ADU must meet. These include requirements for ceiling height, natural light and ventilation, fire access, and separate entrances.

Appendix U of the NYC Building Code was created to establish rules specific to ADUs. Sections such as U101.2 General Conditions set out baseline requirements for making ADUs safe and code compliant.

Appendix U also outlines standards for:

• Fire-rated separations
• Sprinkler systems
• Independent or modified utility connections
• Exit stairs for above-grade units

Rear-Yard ADUs must provide a minimum 5-foot-wide unobstructed access path for safe entry and emergency response.

DOB Rules (1 RCNY §105-08)

In addition to the Building Code, 1 RCNY §105-08 is a DOB rule that establishes technical requirements for ADUs, including:

• Flood mitigation measures
• Water sensors and alarms
• Entrance identification
• Occupancy restrictions

These requirements apply regardless of zoning eligibility and are enforced during DOB plan review and inspections.

Utility capacity and metering considerations

In addition to zoning and Building Code compliance, ADUs must be supported by adequate electrical, gas, and water capacity. Depending on the size of the ADU, appliance selection, and whether utilities are separately metered, a project may require upgrades to existing services.

Common triggers for utility upgrades include:

• Limited existing service capacity, especially in older homes where electrical panels were not designed to support an additional dwelling unit
• Electrification of building systems, such as electric heating, cooling, or cooking equipment, which can significantly increase electrical demand
• Requirements for separate utility metering, which may necessitate new meters, service connections, or panel reconfiguration
• Increased water demand from adding a kitchen, bathroom, or laundry to a new dwelling unit, which can require upgrades to water or sewer connections

Utility upgrades may involve new meters, service connections, trenching, or coordination with utility providers and City agencies. These upgrades can affect cost, permitting timelines, and inspection sequencing and should be evaluated early by your registered design professional (RDP) and contractor.

2. Light, ventilation, and habitable space

Every habitable room in an ADU must have natural light and ventilation, typically through windows that open directly to the outdoors. Windows must meet minimum size and placement requirements to ensure adequate light and airflow for each living space.

Light and Ventilation of ADUs | U103.3

Energy code compliance

ADU projects must comply with the NYC Energy Conservation Code, which governs insulation, air sealing, mechanical ventilation, and system efficiency. Energy Code compliance is reviewed separately from zoning and Building Code requirements.

Documentation demonstrating compliance is required as part of DOB approvals. Missing or incomplete energy filings can delay final inspection and legal occupancy approval, even when construction is otherwise complete.

3. Entrances, egress, and fire department access

ADUs must provide safe, direct access for occupants and emergency responders. The Building Code establishes requirements for separate entrances, compliant egress paths, and fire department access to ensure life safety and emergency response readiness.

Separate Entrance Required | U103.4

An ADU must have its own entrance, directly from outside, or from a shared public hallway inside the main building.

Fire Department Access | U103.8

The main entrance of an ADU must be within 100 feet of the curb line so the fire department can reach it. A clear, unobstructed 5-foot-wide access path, or egress, is required.

These access requirements apply to all ADU types and are strictly enforced during plan review and inspections.

4. Multiple Dwelling Law and ADUs

Two-family homes adding a fire-separated Attached or Detached ADU are exempt from New York State’s Multiple Dwelling Law (MDL).

Other ADU types, such as Basement or Attic ADUs, may trigger MDL requirements including enhanced fire safety, light, and ventilation standards. Your RDP can help determine whether your project qualifies for an exemption.

5. Zoning variances and floor area ratio (FAR)

Understanding zoning variances
If a property cannot comply with zoning rules due to unique physical conditions, a zoning variance may be required. Variances are reviewed by the Board of Standards and Appeals (BSA) and require proof that the hardship is not self-created and that the relief requested is the minimum necessary.

Understanding FAR
FAR regulates how much floor area can be built on a lot and determines whether adding an ADU is physically possible under zoning rules. FAR calculations should be confirmed early by your RDP.

6. Fire protection and sprinkler standards (NFPA 13D)

In nearly all cases, ADUs in New York City must include an automatic sprinkler system conforming to NFPA 13D, as adopted and modified by the NYC Building Code.

• Detached ADUs: Fully sprinklered
• Attached ADUs: Fire-rated separation plus sprinklers
• Basement and Cellar ADUs: Always fully sprinklered

If a building is three or more stories and includes a Cellar ADU, the entire building may be required to be sprinklered.

Additional life-safety systems include smoke alarms (BC §907), carbon monoxide alarms (BC §915), and gas alarms where applicable (BC §918).

7. Inspections and final approvals

Building an ADU in New York City requires multiple inspections, often by different inspectors and agencies. These inspections confirm compliance with approved plans and applicable codes.

Your RDP and general contractor are responsible for coordinating inspections.

DOB inspections

Typical stages include:

• Site and foundation
• Framing
• Rough plumbing
• Rough electrical
• Fire protection
• Insulation and energy code
• Final inspection

Specialty and agency inspections

Depending on the project, inspections may also be required by:

• FDNY (sprinklers, alarms, access)
• DEP (asbestos, water, sewer)
• Utility providers
• LPC
• DOT
• DSNY

Accessibility considerations

Depending on building configuration, unit location, or funding source, accessibility requirements may apply. These can trigger additional design elements or inspections, such as lifts or accessible routes. Accessibility determinations are project specific and should be reviewed early.

8. Final sign-off and legal occupancy

After all inspections and required documentation are complete, DOB issues either a Certificate of Occupancy (CO) or a Letter of Completion (LOC).

Only after this approval may an ADU be legally occupied or rented.

Keep records

Maintain copies of:

• Permits and approved plans
• Inspection results
• Utility sign-offs
• Warranties for safety systems

These records may be needed for refinancing, insurance, or resale.