ADU laws in Arizona

In plain words

Arizona has several state ADU laws. An ADU (accessory dwelling unit) is a smaller second home on the same lot as a house. Arizonans often call it a casita.

A 2024 law covers cities and towns with more than 75,000 people, such as Phoenix, Tucson and Mesa. A 2025 law covers the unincorporated parts of every county, meaning land outside any city or town. In smaller cities and towns, local zoning still decides. Zoning is the set of local rules about what can be built where.

In covered areas, a lot with a single-family house may have one attached and one detached ADU. On lots of an acre or more, a third unit is possible. Cities allow it only if one unit is rented to lower-income tenants; counties may add that condition. These are "permitted uses." That means approval without a public hearing or special permit, often called "by right."

Local governments must allow an ADU up to 75% of the house's floor area or 1,000 square feet, whichever is smaller. They cannot require a side or rear setback of more than 5 feet. A setback is the required gap between a building and the property line. They cannot require extra parking, matching design, fire sprinklers, or a family tie to the tenant. They cannot stop either home from being rented long term.

Two newer laws reach every city and town. Each must offer pre-approved ADU plans or a plan program. City development fees for an ADU are also capped.

Private covenants, such as homeowners association (HOA) rules, still apply, so an HOA can block an ADU. An owner may also have to live on site to rent out a property with a newer ADU short term. Whether you can build still depends on your lot and local rules.

The rules at a glance

What to do next

1. Find out whether you live in a city or town of more than 75,000 people or in an unincorporated county area; if you are in a smaller town, read that town's own ADU code.
2. Check your HOA's CC&Rs before spending money on plans, because state law does not override private covenants that ban or limit ADUs.
3. Pull your plat or title report to find public utility easements, and confirm sewer capacity or septic sizing.
4. Read your city's or county's ADU ordinance and ask for its pre-approved ADU plans; state law now requires every city and town to offer pre-approved plans or a plan program, and Phoenix's are free.
5. Ask for a fee estimate early; city and town development fees for an ADU are capped by a 2026 state law, but county fees and permit fees are not.
6. If you might use the house or ADU as a short-term rental, check the local registration rules and whether you would have to live on the property.

What your town still decides

In covered cities and counties, the state sets minimums and the local code fills in details such as height, design not tied to the main house, and building and fire codes. A local government that missed its deadline (cities 2025-01-01, counties 2026-01-01) must allow ADUs on all residentially zoned lots without limits. Cities and towns of 75,000 or fewer people write their own ADU rules, which range from generous to restrictive; even so, every city and town must offer pre-approved ADU plans or a pre-approved plan program where ADUs are allowed (from July 1, 2026, A.R.S. 9-461.20) and must keep ADU development fees within the 2026 cap (A.R.S. 9-463.05(U)). The state law expressly leaves private restrictive covenants alone, so HOA CC&Rs can still ban or limit ADUs; the government just cannot make a covenant a condition of approval. Owner-occupancy rules are not named in the statute, but because a city or county cannot stop either the house or the ADU from being leased separately as long-term rental housing (90+ days or month to month), a requirement that the owner live on site would conflict with state law; the only owner-residence rule allowed is for short-term rentals.

Examples of local rules

• Phoenix: Updated its rules in late 2024 to follow state law. A lot with one single-family home may have two ADUs, and a third in certain cases. Each ADU may be up to 75% of the main house's floor area, capped at 1,000 sq ft on lots up to 10,000 sq ft or 3,000 sq ft on larger lots. The city offers free pre-approved detached ADU plans from a 2024 design competition with AIA Phoenix Metro. Source
• Tucson: Has allowed casitas (ADUs) in zones that allow homes since January 2022. Mayor and Council adopted HB2720 amendments on October 22, 2024 (effective November 21, 2024), raising the number of ADUs per lot, changing the size formula, adjusting height limits and removing minimum parking requirements. The city now offers a Casita Model Plan Library of pre-designed plans, and Mayor and Council directed staff to create an ADU directory. Source
• Mesa: ADUs are permitted on any lot where a single residence is allowed, including agricultural, residential, mixed-use and some commercial zones. One attached and one detached ADU per lot, plus another detached ADU on lots over an acre if one unit is income-restricted. Size: 1,000 sq ft or 75% of the main home's habitable area, whichever is less. 5-foot side and rear setbacks; height follows the zone. RVs, manufactured homes and tiny homes on wheels cannot be ADUs. Source

What we’re still confirming

• State law names attached and detached ADUs but doesn't say whether a garage or basement conversion counts as attached; ask your city how it treats one.
• Which counties adopted ADU rules by the January 1, 2026 deadline isn't confirmed; if you live outside a city, ask your county planning office.

Laws, bills and citations

This is general information, not legal advice. Your town, village, city or county decides what can be built on your property. If something here looks out of date, email the team.