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An ADU (accessory dwelling unit) is a second, smaller home on the same lot as a house, with its own kitchen, bathroom, sleeping space and entrance. It can be a detached backyard cottage, an addition attached to the house, a converted garage, an apartment over a garage, or a unit inside the house, such as in a basement. You may also see "JADU" (junior ADU), a California term for a small unit inside a house; New York has no such category. Your town decides which of these types it allows.

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The total depends on the kind of ADU, the site, utilities, design and approvals, and what the construction price includes. Published national figures mix conversions with new construction and do not establish a price for your property. Compare the complete scope, including site work and utility connections, and get an itemized estimate before committing to a project. Our cost guide explains the main line items and how to compare quotes.

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Yes, if your town and your lot allow an ADU. Plan one level with a step-free entry, 32-inch clear doorways, a curbless shower, room to turn a wheelchair and wood blocking in the bathroom walls for future grab bars, which cost little on the drawings and a lot once the walls are closed. A single ADU usually doesn't have to meet federal accessibility rules, so these choices are yours. Some towns near Rochester allow an ADU only for relatives, or expect it to come out later, so ask your code office before you design.

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Only if your town allows it, and many upstate towns add conditions, such as requiring the owner to live in the house or the ADU, or allowing the unit only for relatives. If you rent on a regular lease, New York's landlord rules apply to you, including a security deposit of no more than one month's rent. Short-term rentals face their own town rules and, since March 2025, New York sales tax on stays over $2 a day. An ADU built with the state's Plus One grant must be permanent housing, not a short-term rental.

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As rough planning ranges, not promises: about 9 to 18 months where your town requires a special use permit (a board's approval, usually after a public hearing), and possibly under a year where an ADU is allowed with just a building permit. A variance, septic problems or a neighbor's lawsuit can stretch it to two years or more. Under New York Town Law the special use permit alone can take a little over four months, and contractor-built new homes averaged 11.7 months from permit to finish in 2025. Your town's meeting calendar and your builder's schedule set the real timeline.

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Every ADU in New York needs a building permit, and many also need zoning approvals such as a special use permit, site plan review or a variance, plus septic or sewer, water and electrical sign-offs. The homeowner is usually the applicant for zoning approvals, and the builder usually files for the building permit with proof of workers' compensation coverage. A homeowner acting as their own general contractor files a BP-1 form instead, which comes with strict limits.

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