Arizona ADU Law: What HB 2720 (and the 2025 County Expansion) Lets You Build

The statute's definition (§ 9-461.18(I)) is broader than most people expect. An accessory dwelling unit is a self-contained living unit on the same lot as a larger, primary single-family home, with its own sleeping area and its own sanitation facilities. A kitchen is allowed but not required by the definition. The unit can be:

• Detached — the classic backyard casita or guest house;
• Attached — built onto the main house with its own entrance, the in-law-suite pattern; or
• Converted — carved out of existing space, most often a garage.

Whatever you call it — casita, guest house, granny flat, in-law suite, garage apartment — if it's a second self-contained dwelling on a single-family lot, it's an ADU in the law's eyes, and the same rules apply. The one structural constant: the ADU is the accessory, meaning it sits on the same lot as a larger primary dwelling.

On any lot where a single-family home is allowed, a covered city must permit — as a matter of right — at least one attached and one detached ADU (§ 9-461.18(A)). On lots of one acre or more, the city must permit one additional detached ADU, provided at least one ADU on the lot is a restricted-affordable dwelling unit — a unit rented, under a deed restriction or development agreement, to households earning up to 80% of the area median income.

Three things to understand about those numbers:

1. They are floors, not ceilings. A city may allow more. Phoenix, for instance, permits two ADUs in addition to the primary dwelling on single-family lots, per its official ADU page.
2. "Permitted use" means no zoning gauntlet. The statute defines it as approval without a public hearing, variance, conditional use permit, special permit, or special exception. Your neighbors don't get a vote on your casita.
3. Permits still exist. Plan review and building permits still apply, and the city may still check that a site plan conforms to its zoning ordinance. The law removed discretionary approval, not building safety review.

Section 9-461.18(B) reads like a list of every tactic cities historically used to make casitas impractical — and prohibits each one. A covered municipality may not:

• Require additional parking for the ADU, or accept payment in lieu of parking;
• Impose rear or side setbacks greater than five feet from the property line;
• Apply height, setback, lot size, lot coverage, or frontage standards stricter than those for single-family homes in the same zone;
• Require the ADU to match the main house's exterior design, roof pitch, or finish materials;
• Require any familial, marital, employment, or other relationship between the owner or occupant of the main house and the occupant of the ADU;
• Prohibit long-term rental of the main house or the ADU, or the advertising of either for long-term rental;
• Require public street improvements as a condition (except repairing street damage the ADU construction itself causes);
• Require a restrictive covenant on the ADU as a condition of a permit or license;
• Hold the ADU to a commercial building code; or
• Require fire sprinklers in the ADU (§ 9-461.18(D)).

If a covered city's counter staff tells you something on this list is required, the statute is on your side — politely, and in writing.

The ADU law is a limit on city zoning power — not a free pass from everything else:

• HOA covenants survive. Section 9-461.18(C) expressly preserves private restrictive covenants. If your CC&Rs prohibit second dwellings, the state law does not override them. Read your HOA documents first; it's step one of our lot review.
• Building, fire, and health codes apply (§ 9-461.18(D)) — minus the two carve-outs above (no commercial code, no sprinkler mandate). The ADU is inspected like any habitable structure.
• Permits and inspections are unchanged. Plan review, building permits, trade inspections, and a final certificate of occupancy are all still part of the project.
• Utility easements need written consent. An ADU may not be built over a current or planned public utility easement without the written consent of every utility that uses or may use it (§ 9-461.18(E)). Your plat or survey shows these.
• The exemption zones — tribal land, military-airport vicinity, and 65+ decibel airport noise contours — sit outside the statute entirely (§ 9-461.18(G)).

Masizo Development is a licensed Arizona general contractor (AZ ROC #336058) based in Gilbert, building across Gilbert, Mesa, Chandler, Queen Creek, San Tan Valley, Tempe, Scottsdale, Phoenix, Fountain Hills, and Paradise Valley. ADU work — detached casitas and guest houses, attached in-law suites, and garage conversions — is one of our core service lines, and the law above is terrain we navigate on clients' behalf: we review your lot, your assessor records, your HOA covenants, and your easements at a free on-site consultation, then handle design coordination, the permit application, city plan review, construction, and every inspection through final approval.

If you've read this far, you already know more about Arizona ADU law than most contractors you could call. The next step is finding out what your lot supports — tell us about your property or call (602) 909-7630 and we'll walk it with you, no obligation.