Arizona's Casita Law in 2026: HB 2720 ADU Rules Explained

Arizona's "casita law" — House Bill 2720, signed May 21, 2024 and codified at A.R.S. § 9-461.18 — hit its compliance deadline on January 1, 2025. Since then, every Arizona city and town with more than 75,000 residents has been required to allow accessory dwelling units by right on any lot where a single-family home is permitted. Eighteen months in, all 16 covered cities have adopted regulations, and the law has quietly rewritten the rules of backyard building across the Valley. Here is what HB 2720 actually guarantees, how Phoenix, Tempe, and Gilbert implemented it, and how a 2025 follow-up bill extends the same framework to county land.

What HB 2720 requires

The statute sets a floor that covered cities cannot go below: • At least one attached and one detached ADU by right on any lot or parcel where a single-family dwelling is allowed — a permitted use, meaning a building permit, not a hearing or conditional use permit. • A third detached ADU on lots of one acre or more, if one of the units is a restricted-affordable dwelling. • Size: cities must allow ADUs up to 75% of the primary home's gross floor area or 1,000 sq ft, whichever is less (cities may allow more, and several do). • Setbacks: rear and side setbacks for ADUs may not exceed 5 feet . • No parking mandates: cities cannot require additional off-street parking for an ADU, or charge in-lieu parking fees. • No design matching: cities cannot require an ADU to match the primary home's exterior design, roof pitch, or finish materials. • Height: ADU height limits must be no stricter than those for the primary structure. • Rentals: cities must allow the main home and the ADU to be rented separately as long-term housing, and cannot require any familial or ownership relationship between the parcel owner and the ADU occupant. The enforcement mechanism had real teeth: any covered city that failed to adopt compliant regulations by January 1, 2025 would have ADUs allowed on all residentially zoned lots with no restrictions at all . Unsurprisingly, cities complied. How big a change was this? A September 2025 brief from ASU's Morrison Institute (ARCHES) surveyed pre-2720 rules in all 16 covered cities and found that no Arizona city previously allowed more than one ADU per parcel , at least four required dedicated off-street parking, at least three required setbacks larger than 5 feet, and only two allowed ADUs in all residential zones. Gilbert, for instance, required a use permit for casitas on lots of 6,000 sq ft or more. All of that is now preempted.

The short-term rental carve-out

One nuance matters for investors: while HB 2720 bars cities from restricting long-term rental of ADUs, a companion provision (A.R.S. § 9-500.39) lets cities require the property owner to live on the parcel when an ADU is used as a short-term rental — but only for ADUs built after the law took effect in late 2024. Cities have codified slightly different trigger dates (Phoenix uses September 14, 2024; Tempe uses December 20, 2024), so if an Airbnb casita is part of your plan, verify the exact cutoff and licensing rules with your city. Older ADUs are generally grandfathered.

How Valley cities implemented it

Phoenix: beyond the floor on big lots. Phoenix had already adopted an ADU ordinance in 2023, ahead of the state mandate, and its current rules exceed the HB 2720 floor in one important way: on lots over 10,000 sq ft, a detached ADU can reach the lesser of 3,000 sq ft or 10% of net lot area — triple the state minimum. Smaller lots get the standard 1,000 sq ft / 75% cap. Two ADUs (one attached, one detached) are by right, with a third affordable unit possible on acre-plus lots. Full details on our Phoenix ADU rules page. Tempe: streamlined and standard-plan friendly. Tempe amended its code in late 2024 to allow one attached and one detached ADU by right in all single-family districts, at the state-standard 1,000 sq ft / 75% cap with 5-foot setbacks and no added parking. Tempe has also promoted pre-approved standard plans to cut design and review costs — the approach the ARCHES brief specifically recommends cities adopt to turn legal entitlements into actual construction. See our Tempe ADU guide. Gilbert: compliant, if not enthusiastic. Gilbert — a town of roughly 270,000 — replaced its old use-permit casita regime with by-right approval in all single-family districts through its One Stop Shop permit process. The town applies the 75% size standard, the capped 5-foot setbacks, and no parking or design-matching requirements. It is functional compliance without a standard-plan program or incentives; details on our Gilbert ADU page. Neighboring Scottsdale, historically the Valley's most restrictive city, now also allows two ADUs by right, though it caps a second or third unit at 500 sq ft.

HB 2928: the county extension

In 2025 the legislature passed HB 2928, applying the same playbook to county land. Counties must allow at least one attached and one detached ADU wherever a single-family dwelling is permitted, with the same 1,000 sq ft / 75% size floor (and a guarantee that ADUs of at least 650 sq ft of livable space are allowed), an additional affordable unit on parcels of one acre or more, and the same limits on parking and design mandates. The compliance deadline was January 1, 2026 , with the identical penalty: counties that missed it face ADUs permitted on all residentially zoned parcels without limits. For homeowners in unincorporated Maricopa, Pima, and Pinal County, this closes the gap between city and county land.

Honest caveats

Three things the casita law does not do. First, it does not override private HOA covenants — if your CC&Rs prohibit casitas, state zoning law will not save you, and a large share of Valley homes sit in HOAs. Second, it does not waive building codes, utility connection costs, or (except parking in-lieu fees) impact fees, which can add meaningfully to project budgets. Third, there is not yet published statewide data on how many ADU permits have been issued since January 2025 — the ARCHES brief documents the regulatory change, but production numbers will take another year or two to assess. Treat any claim about an Arizona "ADU boom" as anecdotal for now.

The bottom line

Arizona went from one-ADU-maybe-with-a-hearing to two-by-right in a single legislative stroke, and the January 2025 deadline made it real in all 16 large cities at once. If you own a single-family lot in the Valley, you can very likely build a casita today — the question is what your specific city's code, your lot, and your HOA allow. Start with our city guides for Phoenix, Tempe, Gilbert, and Scottsdale for exact setbacks, size caps, and permit steps — then run your project through our free ADU cost calculator to estimate build costs and rental returns for your city.