Tiny home on wheelsNo statewide tiny-home-on-wheels law. Rural counties, especially in the northern and western parts of the state, remain more permissive than most cities for THOWs specifically — that pattern still holds even as the ADU law below has expanded to cover unincorporated county land too.
ADU / accessory unitThis is a further update to an already-strong entry: House Bill 2720 (signed May 2024) required every Arizona city over 75,000 population to allow at least one attached and one detached ADU by right. A follow-on law, House Bill 2928 (signed May 23, 2025, codified alongside A.R.S. §9-461.18 and adding §11-810.01), extends nearly identical requirements to counties — unincorporated Maricopa, Pima, Pinal, and other county land now falls under the same framework. Counties had until January 1, 2026 to adopt compliant regulations; any county that missed that deadline must allow ADUs on all residentially zoned lots by default, with no further local restrictions. Together, HB 2720 and HB 2928 mean Arizona now has one of the most complete statewide ADU mandates in the country — covering both incorporated cities and unincorporated county land, not just one or the other.
Minimum square footageNo statewide minimum; both laws cap ADUs at 75% of the primary home's floor area or 1,000 sq ft, whichever is less
Foundation requirementFoundation-built ADUs now have a strong, confirmed statewide legal path both inside city limits and in unincorporated county land as of the January 2026 county compliance deadline