Which Arizona cities are required to allow ADUs?

In Arizona, a city is required to allow ADUs only if its population is more than 75,000 people. The state ADU law, A.R.S. 9-461.18, says plainly: "This section applies to a municipality with a population of more than seventy-five thousand persons." An ADU, or accessory dwelling unit, is a small second home on a single-family lot with its own sleeping and bathroom space. Cities over that line, like Phoenix, Mesa, Chandler, Scottsdale, and Gilbert, must allow at least one attached and one detached ADU on any single-family lot. Smaller towns, including several Jematell serves, like Carefree, Cave Creek, and Fountain Hills, fall under the threshold and are not forced by this law to allow them. Land outside any city is governed by county law instead, under A.R.S. 11-810.01.

The simple test is population plus jurisdiction. If your lot is inside a city over 75,000, the state mandate covers you. If it is in a small town or out in unincorporated county land, a different rule applies. Knowing which one decides whether you have a legal right to build a backyard casita or have to ask permission.

The rule: 75,000 people is the line

The state ADU mandate binds only Arizona cities with a population over 75,000, and that number is set in the statute itself. A.R.S. 9-461.18 was created to open up backyard housing across the state, but the legislature limited the city mandate to larger municipalities. The exact language in the statute reads: "This section applies to a municipality with a population of more than seventy-five thousand persons." Towns at or below that size are simply outside the law's reach for the city requirement.

For the cities it does cover, the law requires a real, enforceable right to build. A covered city must allow at least one attached and one detached ADU on any lot where a single-family home is allowed. It cannot require extra parking. It cannot set rear or side setbacks greater than five feet. It cannot demand a family relationship between the people in the two units, and it cannot ban renting the ADU as long-term housing. These limits strip away the tools cities once used to block second units. For the full set of standards, see our page on Arizona's ADU requirements for setbacks, size, and utilities.

There was also a deadline. Covered cities had to adopt these rules by January 1, 2025. If a city missed it, the statute says ADUs "shall be allowed on all lots or parcels zoned for residential use" with no local limits. That penalty pushed nearly every covered city to update its code on time.

The mandate grew out of two recent state laws. House Bill 2720, signed in 2024, created the ADU requirement and the 75,000-person threshold. A follow-up law, House Bill 2928 in 2025, refined and expanded it. The goal behind both was to ease Arizona's housing shortage by letting homeowners add small rental units without a city saying no. The legislature targeted larger cities first because that is where most of the state's people and housing demand sit. Smaller towns were left to decide for themselves, which is why the city you are in matters so much.

Which Arizona cities are covered

The covered cities are the large municipalities well over the 75,000-person mark, which includes most of the major Phoenix-metro cities. Based on the 2020 Census, these Arizona cities clearly exceed 75,000 and are bound by A.R.S. 9-461.18:

• Phoenix, the state's largest city at roughly 1.6 million people.
• Mesa, Chandler, Scottsdale, Gilbert, Glendale, and Tempe, all major East and central Valley cities.
• Peoria, Surprise, Goodyear, Buckeye, and Avondale on the West Valley side.
• Tucson, Flagstaff, and the city of Maricopa outside the metro.

These cities have all written the state floor into their own zoning codes, so the fine print varies block to block. Scottsdale adopted its ADU ordinance in 2025 and now allows one attached and one detached ADU on a standard lot, capping the first unit at 1,000 square feet or 75% of the main home, whichever is less. Phoenix allows two ADUs on a standard single-family lot under Phoenix Zoning Ordinance 706, with a third on lots of at least one acre when one unit is deed-restricted affordable. If your lot sits in one of these cities, you have a clear legal path to add a rentable unit, subject to permits and the building code.

Which towns and areas are not bound by the city law

Smaller Arizona towns under 75,000 people are not required by A.R.S. 9-461.18 to allow ADUs, and that includes several communities in the Jematell service area. Because the statute applies only to municipalities over 75,000, these towns keep their own local zoning rules on second units:

• Carefree (roughly 3,700 people).
• Cave Creek (roughly 5,000 people).
• Fountain Hills (roughly 24,000 people).
• Paradise Valley (roughly 12,000 people).

In these towns, whether you can build an ADU depends on the local zoning code, not the state mandate. Some allow guest houses or casitas with conditions. Others restrict them. You have to read the specific town's ordinance and may need a permit or approval the larger cities can no longer require. A town can choose to allow ADUs, but the state is not forcing it to.

Unincorporated land is a separate case. Areas outside any city, like the Rio Verde Foothills in unincorporated Maricopa County, are not governed by the city statute at all. They fall under the county ADU law, A.R.S. 11-810.01, which set a county adoption deadline of January 1, 2026. Maricopa County updated its zoning to allow ADUs on single-family lots in unincorporated areas effective in early 2026. So a rural acreage parcel near Rio Verde follows county rules, not Scottsdale's or Phoenix's. To learn which set applies to your land, see how to know if your lot is in the city or unincorporated county.

What this means for your lot

The practical answer is to start by identifying your jurisdiction, then read the rule that governs it. Your build path depends entirely on where the lot sits.

• In a city over 75,000 (Phoenix, Scottsdale, Mesa, Chandler, and the rest): the state mandate applies, and the city must allow at least one attached and one detached ADU. This is the strongest position.
• In a small town under 75,000 (Carefree, Cave Creek, Fountain Hills, Paradise Valley): the city mandate does not apply. Check the town's own zoning code for what it allows and what approvals it requires.
• On unincorporated county land (Rio Verde Foothills and similar): the county ADU law under A.R.S. 11-810.01 controls, with county standards on size, setbacks, and septic.

Population figures move over time, so a town near the line could cross 75,000 in a future count and become covered. Even in a covered city, you still need a permit, must meet the building and fire code, and must connect utilities. Confirm your lot's jurisdiction and the current population status with the city or county before you design. For a broader primer, see our page on what an ADU is in Arizona and the rules.

Where Jematell Homes comes in

We design to your lot's zoning envelope from the first sketch. We would rather answer your questions before you build than after, so get in touch any time.

Sources

• A.R.S. 9-461.18 (Accessory dwelling units; municipalities; population threshold)
• A.R.S. 11-810.01 (Accessory dwelling units; counties)
• City of Scottsdale: Accessory Dwelling Units (ADUs)
• Phoenix Zoning Ordinance 706 (Accessory Uses and Structures)