Gottlieb Law, PLC provides this article for information purposes only and nothing herein creates an attorney-client relationship. You should not take any actions in reliance on any of the information contained herein without consulting with qualified legal counsel first and reading this article is not a proper substitute for seeking legal advice of your specific situation. Laws change over time and you should seek counsel to discuss any specific legal questions.
A backyard casita can give aging parents their own space, accommodate adult children, or provide rental income. Arizona has expanded the legal framework for accessory dwelling units, but a successful project still starts with understanding the rules that apply to the property.
The current framework includes municipal requirements under A.R.S. § 9-461.18 and separate county requirements under A.R.S. § 11-810.01. Owners considering construction in 2026 should review their property’s jurisdiction, development standards, and private restrictions before committing to plans.
This article provides general information, not legal advice, and does not create an attorney-client relationship. Consult qualified legal counsel about your property and proposed use.
What Arizona’s Municipal ADU Law Requires
A.R.S. § 9-461.18 applies to municipalities with populations greater than 75,000. Subject to statutory exceptions, covered municipalities must allow at least one attached and one detached ADU on a lot where a single-family dwelling is allowed.
For properties measuring at least one acre, the statute requires an additional detached ADU allowance if at least one ADU qualifies as restricted-affordable housing. That designation involves an enforceable affordability restriction, not simply an owner’s intention to charge below-market rent.
The municipal size provision requires an allowance of 75% of the primary home’s gross floor area or 1,000 square feet, whichever is smaller. Local ordinances may provide more generous allowances. Tribal land and specified airport-related areas are excluded from the statutory mandate.
Owners in smaller incorporated communities should check their municipal ordinances rather than assume the large-city mandate applies.
County Properties Have A Separate ADU Framework
A property with a Phoenix mailing address may actually fall within unincorporated Maricopa County. Confirming jurisdiction is an essential first step.
A.R.S. § 11-810.01 requires counties to allow at least one attached and one detached ADU where a single-family dwelling is allowed, subject to statutory exceptions. Counties faced a January 1, 2026 deadline to adopt compliant development regulations.
On parcels of at least one acre, counties must allow an additional detached ADU and may require at least one ADU to qualify as restricted-affordable housing. The statute also establishes a minimum size allowance using the smaller of 75% of the primary dwelling’s gross floor area or 1,000 square feet, while permitting counties to allow larger units.
Maricopa County’s August 2026 directive addresses the affordability restriction required when owners use its additional detached ADU allowance. Owners pursuing that option should understand the documentation and continuing obligations before choosing it.
Parking, Design, And Setback Restrictions Have Limits
Covered municipalities cannot require additional parking or a payment in place of additional parking solely to accommodate an ADU. They also cannot require the unit to match the primary home’s exterior design, roof pitch, or finishing materials.
The law limits rear and side setback requirements to no more than five feet and restricts certain development standards that would treat ADUs more harshly than single-family homes in the same zoning area.
In Phoenix, a garage conversion can raise a separate parking issue. Converting an existing garage or carport requires equivalent replacement parking elsewhere on the lot. Owners should distinguish replacing parking lost through a conversion from adding parking simply because a new dwelling is being created.
Phoenix And Tucson Have Different Development Standards
Phoenix permits two ADUs on eligible single-family detached lots, with a third available under specified acreage and affordability conditions.
For lots measuring 10,000 square feet or less, Phoenix limits each ADU to the smaller of 1,000 square feet or 75% of the primary dwelling’s gross floor area. For larger lots, the maximum is the smallest of:
- 3,000 square feet.
- 10% of the net lot area.
- 75% of the primary dwelling’s gross floor area.
Lot coverage and placement requirements also affect what can actually fit on the property. A generous square-footage allowance does not necessarily mean the entire allowance is buildable.
Tucson’s current code permits two ADUs on qualifying parcels developed with a family dwelling and one on a duplex parcel. Its general size limit is 75% of the principal dwelling’s gross floor area, capped at 1,000 square feet, with an allowance of up to 650 square feet regardless of the principal dwelling’s size. Tucson does not require vehicular parking for ADUs and generally specifies five-foot side and rear setbacks.
Rental Plans Require A Separate Review
Arizona law generally prevents covered municipalities and counties from prohibiting the separate long-term leasing of qualifying ADUs, although private restrictions and other applicable requirements may still affect the property. Owners should evaluate short-term rental plans separately because additional operating requirements can apply.
A.R.S. § 9-500.39 allows a municipality to require the owner of a short-term rental to reside on the property when it contains an ADU whose final approval was issued on or after September 14, 2024. The provision excludes ADUs approved on or before September 13, 2024. It authorizes local regulation rather than automatically imposing the requirement everywhere.
Municipalities may also impose authorized licensing, notification, emergency-contact, and insurance requirements.
County law contains similar authority for an owner-residency requirement tied to the ADU’s approval date. Check the applicable county rules before projecting vacation-rental revenue.
Owners planning long-term rentals should also address lease terms, utility charges, maintenance responsibilities, access, and shared outdoor areas. Clear agreements can help prevent disagreements between occupants of the main residence and the ADU.
HOA Restrictions And Construction Requirements Still Apply
Municipal permission does not resolve private covenant issues. Arizona’s ADU statute preserves private restrictive covenants, so recorded declarations and HOA architectural requirements need their own review. A building permit should not be treated as confirmation that an association has approved the project.
Permitting and safety requirements also remain relevant. State law preserves applicable building, fire, and health regulations, while prohibiting covered municipalities from requiring commercial building-code compliance or fire sprinklers for an ADU. Construction over a public utility easement requires the specified utility consent.
For county properties, septic capacity, drainage, flood control, wildfire prevention, and emergency access can affect feasibility.
Before signing a construction contract, assemble the zoning information, survey, title documents, recorded restrictions, and proposed site plan. Ask the designer and contractor to identify approval responsibilities, utility assumptions, and potential additional costs in writing.
Discuss Your ADU Plans With Gottlieb Law
An ADU project involves more than choosing a floor plan. Unresolved restrictions, disputed property boundaries, or unclear construction agreements can create expensive problems after work begins.
Gottlieb Law can help evaluate the legal issues affecting your Arizona property, review relevant agreements and restrictions, and address disputes that threaten your plans. Contact Gottlieb Law at 602-899-8188 to discuss your proposed casita before making substantial commitments.
Frequently Asked Questions About Arizona ADUs
Can I Build An ADU Anywhere In Arizona?
Eligibility depends on jurisdiction, statutory exceptions, and property conditions. The municipal mandate applies to cities and towns with more than 75,000 residents; county properties have a separate framework.
Does Phoenix Always Limit An ADU To 1,000 Square Feet?
No. Phoenix allows larger units on some lots exceeding 10,000 square feet, subject to its lot-area and primary-dwelling size limits. Lot coverage and other development standards can further affect the permitted design.
Does Tucson Still Allow Only One ADU Per Single-Family Property?
Its current code permits two on qualifying family-dwelling parcels. Different provisions apply to duplex parcels and additional affordable units.
Can My HOA Restrict An Otherwise Permitted ADU?
Private restrictions may remain enforceable. Review the recorded documents and obtain legal advice before relying on municipal approval alone.
Can I Use A New Casita As A Short-Term Rental?
Potentially, but check local operating rules, private restrictions, and any owner-residency requirement tied to the ADU’s final approval date. Construction approval does not establish compliance with every rental requirement.
What Should I Do Before Hiring A Contractor?
Confirm jurisdiction and basic feasibility, review recorded restrictions, and establish who will obtain approvals. Have the construction agreement clearly address scope, allowances, changes, payment milestones, and delays.