How do you build an ADU for aging in place?

Why do families build an ADU for aging in place?

Because it puts help close by without giving up a front door of your own. An accessory dwelling unit (ADU) is a second small home on the same lot as a house. In a 2021 AARP survey, adults 50 and older who would consider living in one gave three top reasons: being near someone while keeping their own space (69%), getting help with daily activities (68%) and saving money (48%) (AARP, 2021).

Most people also want to grow old where they already live. In the same survey, 77% of adults 50 and older said they want to stay in their current home, and about a third said it would need changes for them to stay there safely (AARP, 2021). An ADU is one way to close that gap.

It works in two directions. A parent moves into a cottage in your backyard, close to help but behind their own front door. Or you move into the cottage and a grown child or a caregiver takes the main house. Either one depends on your town and your lot allowing it, and the second one has its own owner-rule and tax traps if the house gets rented.

Caregiving is common, too: about 63 million Americans, roughly one in four adults, were family caregivers in 2025 (AARP and National Alliance for Caregiving, 2025).

What design features make an ADU work at any age?

The short answer is universal design: a home planned to work for people of every age and ability, without looking like a hospital. Most of it costs little on the drawings and a lot once the walls are closed.

A single ADU usually does not have to be accessible by law. The Fair Housing Act’s design rules cover new buildings with four or more units first occupied after March 13, 1991 (US Department of Justice), so in a backyard cottage it is your choice. The ADA Standards were written for public buildings, not homes, but they make a good yardstick.

A zero-step entry has no step at the door. A curbless shower has no lip to step over; the floor slopes to the drain. Blocking is solid wood set inside the wall during framing so grab bars can be screwed in later.

Lighting matters as much as inches. Plan bright, even light in every room, low lights along the path from bed to bathroom, and lights on the walk to the main house. Add the small things too: lever door handles, rocker light switches, slip-resistant floors, a handheld shower with a bench, a comfort-height toilet and laundry on the same floor.

To see these features in one plan, look at our Stay Cottage: one level, one bedroom and about 560 square feet inside, with a zero-step entry, 36-inch doors and a curbless shower. It’s a concept for discussion, not a finished build or an approved plan.

How big should it be, and what layout works?

Keep it on one level, with the bedroom, bathroom, kitchen and laundry all on the same floor. That rules out sleeping lofts and most apartments over a garage, which depend on stairs.

A 2021 survey of California ADUs found the average new unit was 615 square feet, and 61% had one bedroom (UC Berkeley Center for Community Innovation, 2021). Your town’s limit matters more than any average. Near Rochester, East Bloomfield allows a detached family unit of 500 to 850 square feet (Town of East Bloomfield code), Bristol allows 360 to 900 (Town of Bristol code) and the Village of Phelps caps ADUs at 720 (Village of Phelps code).

Ask how your town measures. If it counts to the outside of the walls, the space inside is smaller than the permit number.

In New York: every dwelling unit needs its own toilet, sink, tub or shower, and a kitchen area with a sink (2025 Residential Code of New York State, R326). Without a kitchen, a backyard building is usually treated as an accessory building, not a home.

If the need is urgent. Size and the approval path both change the wait. AARP’s ADU design guide estimates construction at about 4 to 6 months for 300 to 400 square feet, 6 to 9 months for 500 to 600, and 9 to 12 months for 800 to 1,000 (AARP Public Policy Institute, 2019). Where your town allows an ADU with a building permit, as the Town of Canandaigua does (code), there’s no board hearing to wait for. Where a special use permit is needed, state law gives the board up to 62 days to hold a hearing and 62 more to decide, a little over 4 months before the building permit (NY Town Law §274-b). Villages work on a similar clock (NY Village Law §7-725-b). Treat all of these as rough planning ranges, not promises: boards can decide sooner, both sides can agree to extend the clock, and building can take longer than a guide’s estimate.

How do you balance privacy and caregiving?

Plan for both from the first sketch. Each household needs its own door, kitchen and bath, walls that hold sound, and windows that do not look straight into the other home.

Then shorten the trip help has to make. A short, well-lit path to the main house, covered if possible and on the snow-clearing route, matters most in a Finger Lakes winter. An intercom, or a window with a view of the other door, lets someone check in without going outside.

An attached unit puts help a few steps away but is less private. A detached cottage gives more privacy and a longer walk in January. Our In-Law Addition concept shows the attached version, with its own entry plus a door to the main house, and the Stay Cottage shows the detached one.

In New York: an ADU attached to the house is treated like a two-family home, so the walls and floors between the units need a 1-hour fire-resistance rating, or a half hour if the building has full sprinklers (2025 Residential Code of New York State, R302.3).

If a paid caregiver might move in, read your town’s wording. Rush allows relatives or household staff (Town of Rush code), while East Bloomfield allows at most two people related to someone in the main house (Town of East Bloomfield code). A parent and a live-in caregiver sharing the ADU will each need a bedroom.

What are family-only rules?

Some towns allow an ADU only if relatives live in it. A family-only rule, often called an in-law apartment rule, means the unit cannot be rented to the public. That suits a parent’s cottage. It matters later, when the parent no longer needs it.

These rules often add owner occupancy, meaning the owner must live in the house or the ADU. Many also need a special use permit: approval from a town board, usually after a public hearing, which the board may grant or deny.

In New York: there is no broad statewide ADU law, so each city, town and village sets its own rules (Mercatus Center, 2025). A village can differ from the town around it, as the Town of East Bloomfield and the Village of Bloomfield do (Town of East Bloomfield code; Village of Bloomfield code).

These examples from the Rochester and Finger Lakes area link to each code as we last read it. Codes change, so confirm with the town.

Two details catch families off guard:

• Units meant to be temporary. East Bloomfield expects its detached family cottage to be removed when family stops living there (Town of East Bloomfield code). Spencerport requires the added kitchen to come out within six months after the permit ends (Village of Spencerport code).
• Permits that end with a sale or a move. In Penfield, a change in ownership ends the permission (Town of Penfield code). In Rush, the permit ends if the owner moves out or transfers the title outside the rule (Town of Rush code). Before deeding the house to a child, ask what happens to the permit.

Not every town limits who may live there. Bristol’s 2024 law and the Village of Phelps’s 2025 law have no family-only wording (Town of Bristol code; Village of Phelps code). See the New York ADU rules page, or start with the property checker.

Who pays, who owns, and what about Medicaid?

Settle these before anyone writes a check. What follows are questions to ask, not legal, tax or financial advice.

Who owns the cottage? An ADU becomes part of the property it sits on, so a parent who pays to build on a child’s land does not own the cottage. Some local codes bar selling an ADU apart from the house; the City of Geneva’s says so directly (City of Geneva code). Joint ownership, a trust or a life estate (the right to live in a home for life, with someone else owning it afterward) each change taxes, Medicaid and control. An elder law or estate attorney should set this up.

Is the money a gift? The IRS generally treats giving someone a home, or part of one, as a gift, and gifts above the yearly limit need a gift tax return even when no tax is due (IRS, 2026). Ask a tax preparer whether paying for construction, or adding a name to a deed, counts. Rent from a relative below the fair market rate also counts as personal use for tax purposes (IRS Publication 527), so ask how to report it.

What about Medicaid? For nursing-home Medicaid, federal law looks back 60 months at gifts and transfers (42 U.S.C. 1396p). Some home transfers are exempt, such as one to an adult child who lived there for at least two years before the parent entered a nursing home, giving care that let the parent stay home, but the conditions are strict (42 U.S.C. 1396p). See an elder law attorney before money or a deed changes hands, and ask how New York applies these rules today.

Who pays the ongoing bills? A finished ADU adds market value, so expect the assessment and the tax bill to rise (NY Department of Taxation and Finance). Decide who covers that, plus utilities, repairs and insurance. Write it down, along with what happens if the parent moves to a care home, passes away or the house is sold. Tell your insurance agent who will live there before move-in. For building costs and loans, see paying for an ADU.

What this means for you

• Start with the person, not the building. Who will live there now, who might later, and could anyone need a walker or wheelchair? Those answers set the layout and size.
• Build it accessible from the start. The features above are cheap on paper and costly after the walls close.
• Check your town before you design. Is an ADU allowed on your lot, is it family-only, must the owner live on site, and must the unit come out later?
• Plan for the next use. Under a family-only rule, the cottage may sit empty, or have to come out, once the parent no longer needs it.
• Answer the ownership and Medicaid questions first. Setting things up right is easier than undoing a deed.

A planning checklist

Before you design

• Ask your town or village, in writing, whether an ADU is allowed on your lot, which permit it needs and who may live in it.
• Ask what happens to the permit if you sell, move or deed the house to family.
• Not on public sewer? Ask the office that reviews septic systems what yours can handle: the county health department in Monroe, Livingston, Genesee and Seneca, or the NYS Department of Health’s Geneva District Office (315-789-3030) in Ontario, Wayne and Yates.
• Check your deed and any homeowners association rules for limits on a second home.
• Meet with an elder law attorney and a tax preparer about ownership, gifts and Medicaid.

On the drawings

• One level, with the bedroom, bathroom, kitchen and laundry together.
• A zero-step entry with a covered landing.
• Every feature in the design table above.
• Bright, even lighting inside and along the path to the main house.

Before move-in

• A written family agreement covering bills, repairs and what happens later.
• Insurance updated for the ADU and the person living in it.
• A snow plan for the path, the entry and any outdoor heating equipment.

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.