Arizona's casita bill now forces every big-city to allow a backyard casita — and in fact one attached and one detached per single-family lot. Here's how that pairs with the state's modular-insignia program and the desert heat envelope in 2026.
Most Arizonans searching this are looking at a backyard casita in the Phoenix or Tucson metro — for family, for rental income, or both — or a cabin in the high country around Flagstaff and Sedona. The big news for the first group: Arizona's 2025 casita law didn't just legalize one ADU, it requires big cities to allow two (one attached, one detached) per single-family lot. Pair that with the state's modular-insignia program and the only real engineering question left is the desert heat.
The short version: in any Arizona city of 75,000+, your casita is now a right; the state approves the building and tags it with an insignia; and the unit is engineered for heat in the low desert or snow-and-fire up north.
The casita bill: HB 2720 (ARS 9-416.18)
Signed by Governor Hobbs and effective January 1, 2025, HB 2720 requires every Arizona municipality of 75,000 or more to allow ADUs on single-family lots:
- At least one attached and one detached ADU per single-family lot.
- Cities must adopt enabling regulations — they can't ban casitas.
- Cities keep reasonable size, height and setback standards.
That covers Phoenix, Tucson, Mesa, Chandler, Scottsdale, Glendale, Gilbert, Tempe, Peoria, Surprise, Goodyear, Yuma and more. The practical effect: a single lot can carry the main house plus two rentable casitas — a strong investor and multigenerational play. Smaller towns and unincorporated county land aren't covered and follow local rules.
The building: Office of Manufactured Housing
Arizona approves factory-built construction through the Office of Manufactured Housing (OMH) within the Department of Housing:
- OMH reviews the plans against state standards.
- The unit is inspected in-plant during construction.
- An Arizona Insignia of Approval label is affixed certifying the factory-built portion.
- Your local jurisdiction permits the site work — foundation, utilities, zoning — but does not re-review the structure.
The envelope: heat down low, snow and fire up high
- Low desert (Phoenix, Tucson, Yuma). The thermal envelope is everything — insulation, high-performance glazing, reflective roofing, right-sized cooling — to stay efficient through extreme summer heat. Monsoon wind and dust also factor in.
- High country (Flagstaff, Sedona, the Rim). Snow load and wildfire (WUI) cladding take over; a low-desert spec won't pass. Seismic is generally low statewide.
The envelope is set from your site's climate zone at the factory order.
Realistic timeline
- Factory (OMH track): plan review + in-plant inspection + insignia, in parallel with site work.
- Local: a site/building permit for foundation and utilities, plus casita standards. With HB 2720 in force in big cities, the use is allowed by right.
- Set + finish: foundation, set, tie-ins, final inspection.
With the structure built off-site, a turnkey Arizona project can reach handover in roughly four months.
Find your situation
Phoenix/Tucson metro casita. HB 2720 is your green light — and you may be able to add two units. Confirm your city's size/height/setback standards and any STR rules, then the insignia'd unit moves fast.
High-country cabin (Flagstaff, Sedona). Snow and fire spec drive the unit; access and septic drive the site. Engineer the envelope for the mountains, not the desert.
Snowbird / 55+ / multigenerational. A detached casita is ideal for seasonal or family living; the heat-tuned envelope keeps operating costs down.
Hospitality / glamping. Multi-unit production runs in parallel with site work; build to the climate zone of the site.
How PSL Modular fits
We build to Arizona's adopted codes, run the unit through OMH plan review and in-plant inspection for the insignia, and engineer the envelope to your climate zone — desert-heat performance in the valley, snow-and-fire spec up north. UL-listed electrical, ASTM E84 Class A cladding, and helical-pile foundations included. Turnkey from quote to handover in roughly four months.
Next step: tell us your city and whether you want one casita or two, and we'll map HB 2720 to your lot, spec the envelope, and send a real quote.
Sources
- Arizona Department of Housing — Office of Manufactured Housing, Factory-Built Buildings (housing.az.gov)
- Arizona Revised Statutes 9-416.18; HB 2720 (2024, effective Jan 1, 2025)
- Morrison Institute / ASU — HB 2720 ADU policy brief
This guide is general information, current as of 2026, not legal advice. Confirm specifics with your city and the Office of Manufactured Housing.
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The verdict, building-approval path, ADU law, and structural spec for Arizona — at a glance — with a link to a parcel-specific quote.
Frequently Asked Questions
How many casitas can I build on my lot in Arizona?
In cities of 75,000 or more, you can build at least one attached and one detached ADU on a single-family lot. That's the core of HB 2720 (codified at ARS 9-416.18, effective January 1, 2025). Cities must adopt regulations allowing them and can set reasonable standards (size, height, setbacks), but they can't ban casitas outright. Smaller towns and unincorporated county areas aren't covered by the mandate and follow local rules.
Who approves the modular building in Arizona?
The Arizona Office of Manufactured Housing (OMH), within the Arizona Department of Housing. OMH reviews the plans and the unit is inspected during construction; upon passing, an Arizona Insignia of Approval label is affixed certifying the factory-built portion meets state standards. Your local jurisdiction then permits the site work — foundation, utilities, zoning — without re-reviewing the structure.
What's the biggest engineering issue in Arizona?
Heat. Across the low desert (Phoenix, Tucson, Yuma) the design priority is the thermal envelope — insulation, high-performance glazing, reflective roofing, and right-sized cooling — so the unit stays efficient through 115-degree summers. In the high country (Flagstaff, Sedona, the Mogollon Rim) it flips: snow load and wildfire-resistant cladding take over. PSL Modular sets the envelope to your specific climate zone.
Can I short-term rent my casita?
Often yes, but check locally. HB 2720 opened ADU construction statewide in big cities, and Arizona broadly limits cities' ability to ban short-term rentals — but cities can still regulate STRs (licensing, taxes, occupancy). If your numbers depend on nightly rental, confirm your city's STR ordinance before you build.
Does the casita law apply to unincorporated county land?
No. HB 2720 applies to municipalities of 75,000+. On unincorporated county land or in smaller towns, ADUs follow local zoning — which is often permissive, but isn't governed by the state mandate. Confirm with your county planning department.