Arizona ADU (casita) law, explained

What Arizona law lets you build

Arizona's main ADU law is ARS 9-461.18, passed as HB 2720 and signed on May 21, 2024. It applies to cities and towns with more than 75,000 people. In those places, the city must allow, on any lot where a single-family home is allowed:

• At least one attached ADU and one detached ADU, as a "permitted use."
• One more detached ADU on a lot of one acre or more, if at least one ADU on the lot is a restricted-affordable unit.

"Permitted use" means approval without a public hearing, variance, conditional use permit or special exception. The city can still check that your site plan meets the zoning rules.

A restricted-affordable unit is one that, through a deed restriction or an agreement with the city, is rented to households earning up to 80% of area median income.

The law defines an ADU as a self-contained living unit on the same lot as a larger single-family home, with its own sleeping and bathroom facilities. It may also have its own kitchen. [1][3]

What cities can and can't require

The city must allow an ADU that is 75% of the gross floor area of the main home or 1,000 square feet, whichever is less. "Gross floor area" means interior habitable area.

Under the law, a city may not:

• Stop you from renting the house or the ADU separately as long-term rental housing (a lease of 90 days or more, or month to month).
• Require that the ADU occupant be related to, married to or employed by the owner or the person living in the main house.
• Require extra parking for the ADU, or a fee instead of parking.
• Require the ADU to match the main home's exterior design, roof pitch or finishing materials.
• Set height, setback, lot size, lot coverage or frontage rules for ADUs that are stricter than those for single-family homes in the same zone.
• Set side or rear setbacks of more than 5 feet from the property line.
• Require public street improvements, except to repair a street your construction damages.
• Require a restrictive covenant on the ADU.
• Require the ADU to meet the commercial building code or have fire sprinklers.

Building, fire and health codes still apply. You also can't build an ADU on top of a current or planned public utility easement unless every utility that uses or may use it gives written consent. [1]

Deadlines, and what happens if a city doesn't comply

Cities covered by the law had to adopt compliant ADU rules by January 1, 2025. If a city missed that date, the statute says ADUs "shall be allowed on all lots or parcels zoned for residential use in the municipality without limits."

Counties had until January 1, 2026, under the same kind of rule: a county that missed the date must allow ADUs on all residentially zoned lots "without limits."

If your city's rules look stricter than the state law, ask the city's planning department which rules it applies, and read the statute yourself. [1][2]

County land (unincorporated areas)

A 2025 law, ARS 11-810.01 (HB 2928), covers land outside city limits. Counties must allow at least one attached and one detached ADU on any lot where a single-family home is allowed. On lots of one acre or more, they must allow one more detached ADU. The county may require that one of the ADUs be restricted-affordable.

Each ADU must be allowed to be at least 75% of the main home's floor area or 1,000 square feet, whichever is less. Counties may allow larger ones.

Counties face the same limits as cities on rentals, relationships, parking, design matching, 5-foot side and rear setbacks, street improvements and covenants. County rules on wildfire prevention, emergency vehicle access, drainage, flood control and sensitive environmental areas still apply. If your ADU won't be on sewer, or the sewer lacks capacity, the county may require that your septic system be sized for it before you build. [2]

Where the ADU law doesn't apply

The city ADU law does not apply in cities and towns of 75,000 people or fewer. Check your own city's code there.

Neither the city nor the county ADU law applies to lots on tribal land, land near a military airport or ancillary military facility, or land near certain public airports where the noise level is greater than 65 decibels.

The law also doesn't override private agreements. Restrictive covenants made between private parties, such as HOA rules, can still limit ADUs. The city just can't make you sign one to get a permit. [1][2]

Renting your ADU short term

Under ARS 9-500.39, a city or town "may not prohibit vacation rentals or short-term rentals." It may require a local permit, with a fee of no more than the cost of issuing it or $250, whichever is less.

There is one ADU rule. A city may require the owner to live on the property if the property has an ADU whose certificate of occupancy or similar final approval was issued on or after September 14, 2024. That rule doesn't apply if the ADU's final approval was issued on or before September 13, 2024. [4]

Duplexes and middle housing

ARS 9-462.13 (HB 2721, signed May 21, 2024) required cities of 75,000 or more to allow duplexes, triplexes, fourplexes and townhomes as a permitted use by January 1, 2026, on:

• All lots zoned for single-family use within one mile of the city's central business district.
• At least 20% of any new development of more than 10 contiguous acres.

For these homes, the city may not require owner occupancy, require more than one off-street parking space per unit, limit them to less than two floors, or use rules stricter than those for single-family homes in the same zone. If a city didn't adopt rules by the deadline, the law says middle housing is allowed on all single-family lots in the city "without any limitations." [3][5]

Pre-approved ADU plans

ARS 9-461.20 (SB 1529, 2025) says a city must set up standard pre-approved housing plans or a pre-approved plan program. Beginning July 1, 2026, in single-family areas that allow ADUs, the city must create at least three pre-approved ADU plans, each 200, 600 or 1,000 square feet.

Cities must approve or deny plans submitted to the program administratively, without discretionary review, and post approved plans on their website. A city may require you to release and indemnify it as a condition of using a pre-approved plan. Ask your city whether its plans are ready. [6]

Where local rules differ

Each covered city adopts its own ADU regulations, within the limits above. Read your city's rules and confirm the details for your lot with its planning department. See our Phoenix page for how one city applies the state law.

Other state pages: Colorado and Montana. For how permits usually work, see our ADU permit process guide, and for budgets see ADU costs. [1]

Arizona laws to know

• HB 2720 (2024), ARS 9-461.18

  Requires cities and towns over 75,000 people to allow attached and detached ADUs on single-family lots, and limits the rules they can put on them. [1][3]

• HB 2928 (2025), ARS 11-810.01

  Gives homeowners on county land the same basic right to attached and detached ADUs, with a January 1, 2026 deadline for counties. [2]

• HB 2721 (2024), ARS 9-462.13

  Requires cities of 75,000 or more to allow duplexes, triplexes, fourplexes and townhomes on single-family lots near downtown and in part of large new developments. [3][5]

• SB 1529 (2025), ARS 9-461.20

  Requires cities to offer pre-approved housing plans, including ADU plans of 200, 600 or 1,000 square feet starting July 1, 2026. [6]

• ARS 9-500.39 (short-term rentals)

  Bars cities from banning short-term rentals but lets them require the owner to live on site when renting a newer ADU short term. [4]

Questions people ask