Can I build an ADU or casita for aging parents in Arizona?

Yes. In most of the Phoenix metro you can build an ADU (accessory dwelling unit, often called a casita) for aging parents by right. Arizona law makes every city of more than 75,000 people, including Phoenix, Scottsdale, Mesa and Surprise, allow at least one attached and one detached ADU on a single-family lot, and since January 1, 2026 counties must do the same on unincorporated land. Neither a city nor a county can require the person living in it to be related to you, demand extra parking, or make it match the main house. Smaller towns such as Cave Creek, Carefree and Fountain Hills set their own casita rules.

Below is what the law allows, how to choose between a suite, an attached unit and a detached casita for a parent, the design details that let a parent stay in it for years, and what the permit, the lot and the budget will ask of you.

What Arizona law lets you build for a parent

Two statutes set the floor. A.R.S. 9-461.18 binds cities over 75,000 people, and A.R.S. 11-810.01 binds counties. Under both, an ADU is a permitted use on a lot with a single-family home, not a special exception you argue for at a hearing. The county statute says a county "shall adopt development regulations that allow at least one attached and one detached accessory dwelling unit as a permitted use."

The parts that matter most for a family build:

• No relative rule, either way. The law bars a city or county from requiring the occupant to be a family member. That also means you never have to prove your parent is related to you, and the unit stays legal if a caregiver or a long-term tenant lives there later.
• A livable size. The city or county must allow an ADU of at least 75 percent of the main home's floor area or 1,000 square feet, whichever is less. That fits a one-bedroom unit on almost any lot; our page on one and two bedroom ADUs in Arizona works through the numbers.
• Setbacks of five feet. Rear and side setbacks for the ADU cannot be pushed past five feet from the property line, so a casita can sit at the back of the yard, away from the street.
• A second unit on an acre. On a county parcel of one acre or more, the county must allow a second detached ADU. On a city lot of an acre or more, a second detached unit is allowed when one unit is rented at a restricted affordable rate.

Rules still vary by city in the details, so start with your own city's page: Phoenix, Scottsdale or Mesa. In Cave Creek, Carefree and Fountain Hills, which are under the 75,000 line, see whether those towns allow casitas and ADUs.

Suite, attached ADU or detached casita: which suits a parent

Families usually choose among three layouts, and the right one depends on how much help your parent needs now and how much privacy everyone wants.

• A suite inside the house. A bedroom, bath and sitting room off the main home, sometimes with a kitchenette. It is the closest arrangement and the easiest for daily help, and it is how a multigenerational home is usually planned. A unit carved out of the existing house is a junior ADU.
• An attached ADU. Its own entrance and its own living space, joined to the main house by a wall or a breezeway. A parent keeps a front door of their own while help is a few steps away.
• A detached casita. A separate small home in the yard. It gives the most privacy and the clearest path to renting it later, and it is the layout most Arizona families mean when they say casita. See casita vs guest house vs ADU for how the names differ.

Whether to include a kitchen is its own choice. A full kitchen is what makes a unit a dwelling, with the permitting that comes with it. A parent who eats with the family may only need a coffee bar and a small refrigerator; our page on building a guest house without a kitchen explains the trade.

Designing an ADU a parent can age in

An ADU built for a parent should still work when that parent uses a walker or a wheelchair. These features cost little when the unit is framed and a great deal to add later. The National Association of Home Builders, which runs the Certified Aging-in-Place Specialist program, describes universal design as "the design of products and environments to be usable by all people, to the greatest extent possible, without the need for adaptation or specialized design."

• A zero-step entry with a flush threshold, covered so monsoon rain does not pool at the door.
• Doors of 32 to 36 inches and halls of 36 to 42 inches, the range NAHB recommends for a walker or wheelchair.
• A curbless shower. The ADA's roll-in shower, 30 by 60 inches with a threshold of half an inch or less, is a good target even though a private home does not have to meet it.
• Blocking in the bathroom walls so grab bars can go up wherever they are needed later.
• Lever handles and rocker switches, which work with less grip strength, and good lighting, including low lights along the path at night.

Our page on designing an Arizona home for aging in place goes further into each feature.

Arizona details that matter for a parent's casita

• The path between the two homes. Make it level, wide and shaded, with lighting, so a trip to the main house for dinner is safe on a July evening or after dark.
• Its own cooling. A parent who feels the heat more needs a unit that can be cooled on its own schedule. See how to cool a casita separately from the main house.
• Where it sits. A casita you can see from the kitchen, and that a paramedic crew can find from the street, is worth more to a family than one tucked in a far corner. Our page on where to place a casita or guest suite covers the layout.
• Water and septic on rural lots. On a lot with a well or septic system, as is common in the Rio Verde Foothills and Cave Creek, confirm the well and the septic can serve a second home before you design it. The ADU law settles zoning, not utilities.

Permits, timing and an HOA

An ADU for a parent is permitted like any other new dwelling: plans, plan review, a building permit and inspections through to a final. For the plan review and permitting phase, allow 2 to 4 months, depending on jurisdiction, before construction starts. Our pages on getting an ADU permit and how long an ADU takes to build walk through each step.

The state ADU law binds cities and counties, not private covenants. If your home is in an HOA, read the CC&Rs and the design guidelines first; see whether an HOA can block an ADU the city allows.

Cost, taxes and what happens later

The cost depends on the size, whether it is attached or detached, the kitchen, and how far water, sewer or septic and power have to run. Our page on what an ADU costs to build in Arizona breaks down the drivers. A new casita adds to your home's assessed value, so expect a change in property taxes for the part you added, and a permitted unit usually adds to the home's value.

Plan for the years after, too. A unit built for a parent can house a caregiver later, then a grown child, a guest or a long-term tenant. In a city over 75,000 people, state law protects a long-term rental of the ADU; nightly rentals follow separate rules. AARP's guide on ADUs makes the same case: they "expand housing options for people of all ages."

Building a casita for your parents with Jematell Homes

We build casitas, guest houses and ADUs across the Phoenix metro, from Scottsdale and Phoenix to Cave Creek and the Rio Verde Foothills, on a lot you already own or alongside a new custom home. You get weekly progress updates through the build, and we size the unit to your town's size, height and setback rules from the first sketch. Call (602) 421-5576 or tell us about your lot and your parents' needs, and confirm the specific rules for your lot with your city or county planning counter before you commission plans.

Sources

• A.R.S. 9-461.18 (Accessory dwelling units; municipalities)
• A.R.S. 11-810.01 (Accessory dwelling units; counties)
• NAHB: What is Universal Design?
• U.S. Access Board: ADA Standards, Chapter 6 (roll-in showers)
• AARP: The ABCs of ADUs