The Law
Arizona HB 2720 & HB 2928: the new casita law, in plain English
For years, most Arizona cities either quietly banned casitas or made them nearly impossible to build. Two state bills changed that. Here's what actually applies to your lot starting January 2025.
What HB 2720 does
Arizona HB 2720 was signed in May 2024 and took effect January 1, 2025. It's a preemption law — meaning the state overrides local zoning where cities disagree. It applies to Arizona cities with a population above 75,000, which sweeps in almost every major Phoenix-metro city and Tucson.
In those cities, the new state statute requires that on any single-family lot:
- The owner may build at least one attached ADU (part of the main house — a converted garage, addition, or basement unit).
- The owner may also build one detached ADU (a standalone casita, guest house, or backyard unit).
- On lots of one acre or more, the owner may build a third detached ADU if at least one unit is deed-restricted as affordable housing.
What cities cannot require
This is the part most homeowners don't realize. Under the new state law, a covered city may not:
- Require extra parking for the ADU beyond what the primary home already has.
- Require owner-occupancy — you don't have to live in the main house.
- Require matching exterior materials or design to the primary dwelling.
- Impose setbacks greater than 5 feet from side or rear property lines.
- Impose stricter height or lot-coverage limits than the primary dwelling already gets.
In practice this means a city can't kill your casita project with design-review paperwork or a demand that you dig up your driveway to add a parking space.
Size limits
The law caps ADU size, but generously:
- On lots up to 10,000 sq ft, cities must allow an ADU up to 1,000 sq ft.
- On larger lots, the cap is the lesser of 3,000 sq ft or 10% of net lot area.
- An ADU can never exceed 75% of the primary home's gross floor area.
For a typical 1,800 sq ft Phoenix house on a 7,500 sq ft lot, that means you can build up to a 1,000 sq ft casita — plenty for a real 1- or 2-bedroom unit.
What HB 2928 adds (2025)
Signed in May 2025, HB 2928 extends similar rules to certain county-controlled land — meaning unincorporated areas of large Arizona counties. If you're outside city limits in Maricopa or Pima County, the state ADU protections now largely reach you too. Confirm the specifics with your county planning office.
What the law does NOT do
- It does not override private HOA covenants and restrictions. If your neighborhood has an HOA that prohibits ADUs, the state law is not a shield.
- It does not eliminate building permits, impact fees, or standard inspections.
- It does not force cities under 75,000 people to allow ADUs (though many are updating their codes).
- It does not cite a specific section number here — refer to the new state statute; your city planner will know it.
Practical next steps
- Pull your CC&Rs and check for ADU or "guest house" restrictions before spending any money on plans.
- Call your city's planning department, mention the new state ADU statute, and ask for their current ADU checklist.
- Get a survey. Setbacks are five feet minimum — you need to know exactly where your property lines are.
- Talk to a lender before designing. What your lot can build and what you can finance are two different limits.
Frequently asked questions
Does Arizona HB 2720 apply to my city?
It applies to cities with a population above 75,000, which covers most of the Phoenix metro (Phoenix, Mesa, Scottsdale, Chandler, Gilbert, Glendale, Tempe, Peoria, Surprise) and Tucson. Smaller cities and towns aren't required to follow it, though many are updating their codes anyway. HB 2928 extends similar rules to certain county land.
Can my city still require a permit?
Yes. The law limits what cities can require, but standard building permits, health, and safety inspections still apply. Confirm the process with your city's planning department.
Does the law override my HOA?
No. HB 2720 restricts what cities can do. Private HOA covenants (CC&Rs) are separate contracts. If your HOA prohibits ADUs, the state law does not by itself force them to allow one. See our HOA rules page.
How big can my casita be?
For lots up to 10,000 sq ft, cities must allow up to 1,000 sq ft. For larger lots, the ADU can go up to the lesser of 3,000 sq ft or 10% of the net lot area — and never more than 75% of the primary home's gross floor area.
Can the city require me to live in the main house?
No. Owner-occupancy requirements are specifically prohibited under the new state statute.