Arizona ADU Law Forces Big Cities to Allow Backyard Units (ARS 9-461.18)

The statute strips large Arizona cities of most tools they once used to block backyard homes. An ADU may be up to 75 percent of the main dwelling's gross floor area or 1,000 square feet, whichever is less, and a city cannot impose a smaller cap. Municipalities may not require extra parking, matching exterior design, a familial relationship between occupants, restrictive covenants, or side and rear setbacks greater than five feet, and they may not bar renting the ADU as separate long-term housing. Lots of one acre or more can add a second detached ADU if one unit is restricted-affordable. The mandate binds only municipalities over 75,000 residents; smaller towns and unincorporated county land are not covered.

The statute penalizes cities, not owners: a municipality over 75,000 that failed to adopt conforming rules by January 1, 2025 forfeits authority to limit ADU size, setbacks, or parking and must permit accessory dwelling units on every single-family lot.