How do ADU permits work, from idea to move-in?

What are the steps from idea to move-in?

An accessory dwelling unit (ADU) is a small second home on the same lot as a house. Building one means passing two separate checks. The first is zoning, the local law that says what can be built where. The second is the building code, which makes sure the unit is built safely.

Here are the steps, in order. Not every project needs every one.

1. Check that it’s allowed. Make one call to your town’s code office, the local office that handles zoning and building permits, before you pay for drawings.
2. Get drawings made.
3. Get zoning approval if your town requires it. This can mean a public hearing, a meeting where neighbors can speak before a board decides.
4. Get a building permit.
5. Line up utilities: septic or sewer, water, power, and a free call to 811 before digging (UDig NY, 2026).
6. Build, with inspections along the way.
7. Get your certificate of occupancy, the town’s OK to move in.

Zoning comes first because drawings are wasted money if your town won’t allow the unit.

How long does the whole thing take?

As rough planning ranges, not promises:

• About 9 to 18 months from your first call to move-in, where your town requires a special use permit. That’s a board’s case-by-case approval, usually after a public hearing.
• Under a year is possible where an ADU is allowed with just a building permit.
• Two years or more can happen if you need a variance, which is an exception to a zoning rule, or if you run into septic problems or a neighbor’s lawsuit.

These ranges are our own estimate. We built them by adding up the legal deadlines and build times below. Here’s how long each step can take:

• Checking that it’s allowed: we found no public data. It can be as quick as one call.
• Drawings: it varies by project (AARP, 2019).
• Zoning approval: for a special use permit in a New York town, the board must hold a hearing within 62 days of getting your application and decide within 62 days after that (NY Town Law §274-b). A county review, if your lot needs one, gets up to 30 days (NY GML §239-m).
• Building permit: we found no state deadline for the town’s review. One town says work must start within 6 months, and the permit lasts 1 year (Town of Fremont, 2025).
• The 811 call: make it at least 2 and no more than 10 working days before digging (UDig NY, 2026).
• Building: new US single-family homes took 7.4 months on average from start to finish in 2025. When the owner hired a contractor, they took 11.7 months from permit to finish (NAHB, 2026).
• Certificate of occupancy: the town issues it only after the final inspection and paperwork are done (19 NYCRR Part 1203).

We could not find national data on ADU build times, so new-home figures are the closest stand-in. Small doesn’t mean fast: homes under 1,200 square feet averaged 12.2 months from permit to finish (NAHB, 2026). AARP’s ADU design guide estimates about 4 to 6 months of building for a 300 to 400 square foot unit and 9 to 12 months for 800 to 1,000 square feet (AARP, 2019).

Which approvals might your town require?

New York has no statewide law that makes ADUs legal everywhere, so your town’s code is the rulebook (see our New York page). You won’t need every approval below. Our guide on how to check your town’s rules shows how to find out which ones apply.

• Zoning permit or sign-off. Some towns issue a separate land-use permit first. In others, the code enforcement officer (the local official who reviews permits and does inspections) checks zoning as part of the building permit.
• Site plan review. A planning board looks at where the building sits, the driveway, parking and screening.
• Special use permit. The town allows ADUs in principle, but a board must approve each project, usually after a public hearing, and it can attach conditions.
• Variance. An exception granted by the zoning board of appeals (ZBA). An area variance bends a measurement, like a setback (the required distance from a property line). A use variance allows a use your district doesn’t permit. It requires proof of “unnecessary hardship,” which is hard for a typical homeowner to show (NY Town Law §267-b).
• Environmental review. New York’s environmental review law, called SEQR, exempts many homeowner projects, including area variances for one- to three-family homes (6 NYCRR §617.5). If your board decides it applies, you fill out a short form.

Fees vary by town. One small Steuben County town charges $25 to apply for a special permit and $50 for a variance (Town of Fremont, 2025).

In New York: The board that handles special use permits in a town must hold a public hearing within 62 days of receiving the application. Notice is mailed to you and the county planning agency at least 10 days ahead and published in a local paper at least 5 days ahead. The board then has 62 days after the hearing to decide, and it files the decision within 5 business days (NY Town Law §274-b). Both sides can agree to extend those clocks. Added up, the legal outer limit is a little over four months. Anyone harmed by the decision, including a neighbor, then has 30 days to ask a court to review it. Villages follow nearly the same timing (NY Village Law §7-725-b).

In New York: Some lots also need a county review. That happens when your lot is within 500 feet of a town, village or city line, a county or state road or park, a county drainage channel, county or state land with a public building on it, or a farm in an agricultural district. It covers special use permits, site plans and variances. The county gets 30 days to weigh in. If it says no or asks for changes, your local board can still approve, but it needs a bigger vote than usual (NY General Municipal Law §239-m). Ask at your first visit whether your lot is one of these.

Who does what?

This split is common, not a rule. Your contract should say who handles each piece.

What documents will you need?

Ask your town for its own checklist. New York projects commonly need:

• Deed and HOA documents, to catch private rules that can limit building.
• A boundary survey by a licensed land surveyor. The state requires the building permit site plan to be drawn from an accurate boundary survey (19 NYCRR Part 1203).
• A site plan showing the new unit, existing buildings, distances to lot lines, grades and any flood areas (same source).
• Construction drawings. State law doesn’t require an architect’s or engineer’s stamp for a home of 1,500 square feet or less, not counting garages, porches and unlivable spaces (NYSED). Towns may require one anyway; one town requires stamped plans for all new construction (Town of Fremont, 2025).
• Energy code paperwork, a written statement of how the design meets the energy code (19 NYCRR Part 1203). Some towns name a REScheck report on their forms (Town of Jay, 2023).
• A septic design by a licensed design professional if the lot isn’t on public sewer (10 NYCRR Appendix 75-A). Our guide to site and utilities covers septic in more depth.
• Workers’ comp and disability proof, or a state exemption form. A town can’t issue a building permit without it (General Municipal Law §125, as reprinted on the Town of Fremont application, 2025).
• An agricultural data statement if the lot is in, or within 500 feet of, a farm in a county agricultural district and you need a special use permit, site plan or use variance (NY Town Law §283-a).
• An owner-occupancy affidavit where the code requires the owner to live on site. The Village of Pittsford, for example, requires a notarized one (Village of Pittsford §210-24.3).
• Manufacturer labels and installer paperwork for a factory-built unit, which the inspector checks before the certificate of occupancy (19 NYCRR Part 1203). See how ADUs are built.

What inspections happen, and when can you move in?

New York’s statewide rule tells towns to inspect each of these stages that applies to your project (19 NYCRR Part 1203):

• The work site, before the permit is issued
• Footings and foundation, and the prep for any concrete slab
• Framing
• Structural, electrical, plumbing, mechanical and fire-protection systems
• Fire-resistant construction, wood stoves, chimneys and gas vents
• Energy code items such as insulation, windows and air sealing
• Installation of a factory-built unit
• A final inspection when all the work is done

Work has to stay exposed until the inspector accepts it. If it fails, it stays open until it is fixed and checked again, and the inspector must point to the code section that wasn’t met (same source). Several towns also require electrical work to pass an approved third-party inspector before the final (Town of Chenango; Town of Jay, 2023). One town asks for 48 hours’ notice before each inspection (Town of Fremont, 2025).

The certificate of occupancy (CO) is the town’s written confirmation that the unit matches the approved plans and is fit to live in. The town issues it only after it has inspected the work and reviewed any required reports, flood certifications, energy test results and factory labels (19 NYCRR Part 1203). A temporary CO is possible for a set period, but only if the space is safe, the smoke and carbon monoxide alarms work, and all required exits exist (same source).

After the CO, call your insurance agent about covering a second home on the lot. A finished ADU can raise your property assessment, though some places have adopted a state-allowed tax break on the added value (NYS Tax Department). Ask your assessor. If you plan to rent the unit, talk to a tax preparer.

What slows projects down?

What this means for you

• Start with zoning, not design. One call to the town’s code office can tell you whether an ADU is allowed with just a permit, needs a special use permit, or isn’t allowed at all. Our property checker is a good first step.
• If you need a special use permit, plan for months. In a New York town the legal clock runs to a little over four months before a filed decision, plus 30 days in which a neighbor can ask a court to review the decision (NY Town Law §274-b).
• Plan on most of a year to build. Contractor-built homes took 11.7 months from permit to finish on average in 2025 (NAHB, 2026). Your project may be faster or slower.
• Get the paperwork right once. A missing survey or form is the cheapest delay to avoid.
• Don’t move in early. One town’s form says it plainly: no one may use the building until it passes the final inspection and gets its certificate (Town of Fremont, 2025).
• Bring in help where the stakes are high: a surveyor for the boundary, a licensed professional for septic and any stamped drawings, and a lawyer for variances, neighbor disputes or contracts.

This is general information, not legal advice. Your town’s code office and boards have the final say.

General information, not legal, tax or financial advice. Your municipality decides what can be built, and a professional should review decisions about money and contracts.