What did HB 2720 change for building a casita or ADU in Arizona?

House Bill 2720, signed in 2024 and codified at A.R.S. 9-461.18, requires Arizona cities and towns of more than 75,000 people to allow accessory dwelling units (ADUs) on lots where a single-family home is allowed, and it caps how restrictive those cities can be. A 2025 law, HB 2928, added A.R.S. 11-810.01, which puts the same floor on every Arizona county from January 1, 2026, so unincorporated county land, including the Rio Verde Foothills, is now covered too. The live answer on casitas covers the basics of what an ADU is; this one focuses on what the two statutes changed and where they do and do not reach.

What the law requires of larger cities

For covered cities, an outright ban is no longer allowed. A.R.S. 9-461.18 directs them to permit ADUs on any lot where a single-family home is allowed, and it limits the conditions a city can attach. Each city writes its own ordinance within these guardrails:

• At least two ADUs per lot. Covered cities must allow at least one attached and one detached ADU as a permitted use, and one more detached ADU on a lot of one acre or more if one unit on the lot is restricted-affordable housing.
• A size floor. A city must allow an ADU of 75% of the main home's floor area or 1,000 square feet, whichever is less.
• No added parking. A city cannot require extra parking for an ADU, or a fee in place of it.
• Setbacks. ADU rules cannot be stricter than the house's on height, setbacks, lot size or coverage, and side and rear setbacks cannot exceed five feet from the property line.
• Long-term rental and occupants. A city cannot ban leasing the house or the ADU as separate long-term rentals, and it cannot require the ADU's occupant to be family or an employee.
• No matching design. A city cannot require the ADU to match the main home's exterior design, roof pitch or finishing materials.

Cities had until January 1, 2025 to adopt compliant rules, so the larger Phoenix-metro cities now have them. Among the markets we build in, Scottsdale and Phoenix clear the 75,000-resident threshold and are covered.

What HB 2928 added for county land

HB 2928 (Laws 2025, chapter 217, signed May 23, 2025) created A.R.S. 11-810.01, the county version of the rule. Every Arizona county had to adopt ADU rules by January 1, 2026; a county that missed the date must allow ADUs on all residential lots without limits. The county rule tracks the city one, with a few differences that matter on rural land:

• Two ADUs, and a third on an acre. A county must allow one attached and one detached ADU wherever a single-family home is allowed, and at least one more detached ADU on a lot of one acre or more. The county may require one unit on that lot to be restricted-affordable, and Maricopa County does: its zoning ordinance (Article 602.3.2.B) calls for a recorded deed restriction before the permit for the extra unit issues.
• The same size floor, setbacks and parking limits as the city rule: at least 75% of the home or 1,000 square feet, whichever is less, side and rear setbacks of no more than five feet, and no added parking.
• Septic sized first. Where the ADU will not be on sewer, the county may require the septic system serving it to be adequately sized before construction.
• Short-term rentals. A county still cannot ban short-term rentals (A.R.S. 11-269.17), but it may require the owner to live on the property to run one when the lot has an ADU whose certificate of occupancy or final approval was issued on or after September 14, 2024.

Maricopa County's Board of Supervisors adopted its updated zoning ordinance, with the multiple-ADU rules, on December 10, 2025. That covers unincorporated communities such as Rio Verde and the Rio Verde Foothills, where many lots are an acre or more in the Rural-43 zone.

What the laws do not change

Both statutes set a floor, not a free pass. Several things still govern whether and how you can build:

• Smaller towns are not covered. Cave Creek, Carefree, Fountain Hills, and similar towns fall under the 75,000-resident threshold, and as incorporated towns they are not county land either, so their own zoning controls.
• Septic and water capacity still bind. On a lot served by a well and septic, a second dwelling can require a larger or upgraded onsite wastewater system reviewed under Arizona Department of Environmental Quality standards, regardless of what zoning allows.
• Short-term rental is regulated separately. The laws address the right to build an ADU, not the right to operate it as a nightly rental; those rules live in other statutes and ordinances.
• Overlays and codes still apply. Building and fire codes, hillside, drainage and flood rules, and design review continue to shape where an ADU can sit, though neither a city nor a county can require an ADU to meet the commercial building code or carry a fire sprinkler.

Why the distinction matters for your lot search

Two parcels a few miles apart can carry different ADU rights because one sits in a city above the population threshold or in unincorporated county land, and the other in a small town. If a casita or future rental is part of your plan, confirm the jurisdiction before you make an offer, not after.

How Jematell Homes helps

We design custom homes with casitas and ADUs across the metro and tailor each unit to the lot's jurisdiction, zoning, and your goals, whether that is multigenerational living, guests, a home office, or a future rental. Because each covered city and county writes its own rules within the statutes, and small towns sit outside them, we confirm the current standards with your local AHJ, and any applicable HOA, before finalizing a design.

Most of our gallery homes are in Rio Verde, where the county rule now applies. See the casitas and guest houses we build, or contact us with your lot's address.

Sources

• A.R.S. 9-461.18 (Accessory dwelling units; municipalities)
• A.R.S. 11-810.01 (Accessory dwelling units; counties)
• Laws 2025, chapter 217 (HB 2928)
• Maricopa County: Restricted-Affordable Accessory Dwelling Units