If you have heard that Arizona made it easier to build a casita, that is true. What most coverage leaves out is who the law actually covers, and how much it leaves untouched.
First question: is your city even covered?
This is where a lot of people get tripped up. The law does not apply statewide. It reaches cities with more than 75,000 people (A.R.S. 9-461.18(H)), and population means the last decennial census, so the 2020 count is what governs, not this year’s estimate (A.R.S. 1-215).
Phoenix, Mesa, Chandler, Scottsdale, Gilbert, Glendale, Tempe, Peoria, Surprise, Goodyear, Avondale, and Buckeye are all above the line, and so is Flagstaff. Paradise Valley, Prescott, Sedona, and Queen Creek are all below it. Two neighbors twenty minutes apart can be working from completely different rules.
If your city is covered, here is what it owes you
Start with the number that surprises people: it is two units, not one. On a lot where a detached house is allowed, the city has to permit at least one attached and one detached unit (9-461.18(A)(1)). If your lot is an acre or more, a third detached unit is required when one of them is restricted affordable housing (9-461.18(A)(2)).
On size, the city has to allow at least 75 percent of your house or 1,000 square feet, whichever is smaller (9-461.18(A)(3)). Read that as a floor, not a ceiling. Cities can go further, and some do. Buckeye set no square foot cap at all (3.3.4.A.4).
One more thing worth knowing: the statute says “permitted use,” which means your casita cannot be made to depend on a hearing, a variance, or a conditional use permit (9-461.18(I)(5)). You are not asking permission. You are meeting requirements.
And here is what your city can no longer ask of you
The statute took several tools off the table (9-461.18(B)):
- No extra parking, and no fee instead of parking
- No requirement that the casita match your house in design, roof pitch, or materials
- No side or rear setback deeper than five feet
- No requirement that whoever lives there be related to you or work for you
- No ban on renting it separately from the house on a long term lease, meaning 90 days or more, or month to month (9-461.18(I)(3))
There is also a real consequence for cities that ignored all this. Any covered city that missed the January 1, 2025 deadline to update its code has ADUs allowed on every residentially zoned lot in the city, without limits (9-461.18(F)).
Now the part people find out too late
Your HOA can still say no. The statute expressly preserves covenants between private parties (9-461.18(C)). If your CC&Rs prohibit a second dwelling, none of the above helps you. Read them first, before you spend a dollar on anything else. There is a flip side worth knowing though: your city cannot make you record a covenant as a condition of approving the unit (9-461.18(B)(8)).
Airbnb is a separate question. A city may require you to live on the property if you use the unit as a vacation rental, but only when it received its certificate of occupancy or similar final approval on or after September 14, 2024 (A.R.S. 9-500.39(B)(9)). Approved on or before September 13, 2024 and you are outside that rule. It turns on a single date, so find out which side of it you are on early.
Some parcels are carved out entirely. Tribal land, and land near a military airport (9-461.18(G)(1) and (G)(2)). Land near civilian airports is excluded only where noise tops 65 decibels, a limit added in 2025 by HB 2928 (9-461.18(G)(3)). That change sent cities back to redraft. Scottsdale adopted Ordinance 4687 in September 2025 for exactly this reason.
And the law cannot make your lot work. This is the one we see most. A statute can permit a casita your particular parcel still cannot hold. Easements, lot coverage, grading, floodplain, and where the utilities actually run are settled by the site, not by the legislature.
What if your city is below the threshold?
You are not outside state ADU law entirely, which surprises people. A 2025 statute, A.R.S. 9-461.20, requires cities to offer preapproved ADU plans and carries no population threshold at all. Buckeye has three posted. Flagstaff has a library of twelve.
A preapproved plan is a genuine head start on the building. It is not a permit, and it is not a site plan. Your lot still needs its own.
The four below threshold cities we work in each wrote their own rules, and they are nothing like each other. Paradise Valley calls it a guest house and measures by ground area. Prescott counts every accessory building on the lot toward one total. Sedona adopted its framework in November 2024. Queen Creek wrote the threshold into its own code: its expanded allowance switches on automatically once the town’s population crosses 75,000 at a decennial census (Queen Creek Zoning Ordinance 6.1.D.1.q).
Where to start
Read your CC&Rs. Then find out whether your city is covered, and what it did with the room the state left it. Our city pages list the current rules with the code section behind each one.
Sources: A.R.S. 9-461.18. A.R.S. 9-461.20. A.R.S. 9-500.39. A.R.S. 1-215. HB 2720 (2024). HB 2928 (2025). Buckeye Development Code 3.3.4.A. Scottsdale Ordinance 4652 and 4687. Last checked August 2026.