ADU Guide · Verified 2026
Building an ADU in Arizona
Arizona has a statewide ADU law, but it targets larger cities. Under HB 2720 (the "Casita Bill," signed May 2024 and codified at A.R.S. § 9-461.18), any municipality with a population of 75,000 or more must allow at least one attached and one detached ADU as a permitted use on lots zoned for single-family homes. Those cities cannot require extra parking, owner-occupancy, or matching exterior design, and cannot set rear or side setbacks greater than five feet. Smaller towns and unincorporated county land are not covered by the state mandate.
Quick Facts
Statewide floors set by Arizona Revised Statutes § 9-461.18 (HB 2720, 2024, chap. 196). Your city may be more generous but cannot go below them.
The Three Types of ADU
What you can build by right
In a municipality of 75,000 or more, HB 2720 requires the city to allow at least one attached and one detached ADU as a permitted use on any lot where a single-family home is allowed (A.R.S. § 9-461.18). The city cannot set height, setback, lot-size, lot-coverage, or building-frontage rules for the ADU that are more restrictive than those for a single-family home in the same zone, and rear and side setbacks specifically cannot be required at more than five feet. On lots of one acre or larger, a third detached ADU must be allowed if at least one of the units is a deed-restricted affordable unit.
Which cities are covered
The mandate applies only to the 16 Arizona municipalities with populations over 75,000 — the large cities and suburbs (Phoenix, Tucson, Mesa, Chandler, Scottsdale, Glendale, Gilbert, Tempe, Peoria, Surprise, and similar). If your property is in a smaller town or in unincorporated county land, HB 2720 does not force ADU approval, and you are governed entirely by local rules — which may or may not allow an ADU. The first step is always to confirm whether your city meets the 75,000 threshold.
Size limits
On lots of one acre or more, a covered city may cap an ADU at 75% of the interior habitable floor area of the main dwelling, or 2,000 square feet of interior habitable area, whichever is less — and underlying lot-coverage standards for the zoning district still apply. On smaller lots the size is governed by the requirement that ADU standards not be more restrictive than those for a single-family home in the same zone, so the practical cap comes from the zone's own dimensional rules rather than a separate ADU number.
You do not need a family relationship or to live on site
A covered city cannot require that the ADU occupant be a relative of the people in the main house, and cannot impose an owner-occupancy requirement for long-term rental — so you can rent both the main home and the ADU to unrelated tenants on long-term leases. This removed one of the most common pre-2024 restrictions, where many cities required the owner to live on the property or limited the ADU to family use.
Short-term rentals work differently
The long-term-rental protections do not extend to short-term (vacation) rentals. Under a separate statute, A.R.S. § 9-500.39, a city may require that the property owner reside in the primary unit if the ADU is used as a short-term rental. So if your plan is to run the ADU as an Airbnb-style rental, owner-occupancy can still be imposed — confirm your city's short-term-rental ordinance before counting on that income.
Parking and design cannot be piled on
A covered city cannot require additional off-street parking as a condition of an ADU, and cannot force the ADU to match the exterior materials, roof pitch, or finishing of the main house. It also cannot demand public street improvements as a condition of permitting, except where genuinely necessary to reconstruct or repair a public facility. These prohibitions remove the design-and-parking hurdles that cities historically used to discourage ADUs.
You still need a permit
HB 2720 removes zoning barriers, not the building permit. An ADU still requires permits and must comply with local building codes for structural safety, utility connections (plumbing, electrical, sewer or septic), and fire/emergency access. A tiny-home-style ADU is built to IRC Appendix Q standards. Building without the required permits can lead to fines or an order to remove the unit, so pull the permit and pass inspections even though the land-use approval is now guaranteed.
HOAs after HB 2720
The law raises real questions for homeowners associations, which historically restricted ADUs through CC&Rs. HB 2720 constrains what municipalities can do, and some prior HOA and zoning-board restrictions may no longer hold up — but the interaction between the state mandate and existing private HOA covenants is still being worked out. If your property is in an HOA, review your CC&Rs and get legal advice before assuming the state law overrides them.
What people get wrong
The biggest misconception is that HB 2720 legalized ADUs everywhere in Arizona. It did not — the mandate applies only to cities of 75,000 or more. A homeowner in a small town or on unincorporated county land has no state guarantee and must check the local ordinance. The second misconception is that the long-term-rental freedom covers short-term rentals; it does not, and owner-occupancy can still be required for Airbnb-style use.
From Idea to Move-In: The Timeline
Who Administers It
Counties With Their Own Rules
These Arizona counties have verified, county-specific ADU rules that add to the state baseline:
Check Your County
Select your county for local rules, fees, and your building department's contact details:
Building It Yourself? Here's What You'll Need
Planning an ADU? Tools homeowners use in the design and layout phase:
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Check Your Local Rules
Your city may allow more than the state floor
State law sets the minimum; many Arizona cities are more generous. Confirm specifics with your local planning department.
Find your county building department →Not sure if your project needs a building permit, a zoning approval, or both? See our guide to building permits vs. zoning approval.
Official Sources
ADU law changes frequently and local ordinances add detail. This guide is general information, not legal advice — always confirm with your local building department. Reviewed by the StateDataIndex Editorial Team · Updated August 2026.