The Different Types of ADUs in New York City

An Accessory Dwelling Unit (ADU) in New York City is defined as a dwelling unit additional to a one- or two-family home with a kitchen and plumbing.   Homeowners frequently use ADUs to generate extra rental income, provide housing for family members, or offer guests private accommodations.  ADUs can be categorized as detached, attached or interior conversions.

Detached ADUs

As the name suggests, detached ADUs are built completely separate from the primary home but share the same zoning or tax lot.  Detached ADUs are either newly constructed structures built in the backyard of a property, or conversions of existing detached accessory structures such as a garage.

Detached ADUs are the most coveted type of ADU because they offer greater privacy for people living in the main home and the ADU, and tend to increase property values more than other types of ADUs.

Attached ADUs

An attached ADU typically consists of a horizontal addition or extension to the rear of the main home.  Attached ADUs can also be built on top of a portion of the main home.  In either case, attached ADUs are physically connected to and share at least one wall with the primary dwelling.

Attached ADUs are ideal for properties with smaller backyards.  However, they provide less privacy than detached ADUs and generally cost as much to build, if not more so.

Interior Conversion ADUs

This category consists of ADUs created by reconfiguring the interior of a one- or two-family house without adding more square footage to the property.  The most common examples of interior conversion ADUs are attic, basement and cellar conversions.

Interior conversion ADUs are a great way to maximize the value of infrequently used attics, basements and cellars, and they are usually much cheaper to build than detached and attached ADUs.  However, interior conversion ADUs offer the least amount of privacy and can be very disruptive to homeowners during construction.

How to Choose the Right Type of ADU

Homeowners should weigh the costs and benefits of each type of ADU and factor in the preferred end-use of the ADU before deciding how to proceed with their project.  Some properties are excellent candidates for interior conversion ADUs, while others are perfect for detached or attached ADUs. 

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