What are Arizona's ADU requirements for setbacks, size, and utilities?

Arizona's ADU (accessory dwelling unit) requirements set a clear floor that cities and counties cannot drop below. The state caps rear and side setbacks at five feet from the lot line, sizes an ADU at 75% of the main home's floor area or 1,000 square feet, whichever is less, and forbids cities from requiring extra parking. Every ADU still needs its own sleeping and bathroom space and a working hookup to water, sewer or septic, and electricity. These rules come from A.R.S. 9-461.18 for cities over 75,000 people and A.R.S. 11-810.01 for counties. Your specific city can add detail, but it cannot undercut the state minimums.

The requirements split into a few buckets: setbacks and placement, size, utilities, parking, and rental rules. Below is what each one means for a real Arizona ADU, and where Phoenix and Scottsdale add their own fine print.

Setback and placement requirements

State law caps ADU setbacks at five feet from the rear and side property lines, and a city cannot require more. A setback is the minimum distance a structure must sit from a lot line. Both A.R.S. 9-461.18 and the county statute say a government may not "set rear or side setbacks for accessory dwelling units that are more than five feet from the property line." That five-foot floor is a big deal, because it lets you build a detached casita close to the back fence and keep your usable yard.

Cities fill in the rest of the placement rules:

• Front yard. A detached ADU usually cannot sit in the required front yard. Scottsdale's standards keep a detached ADU out of the required front and side yards, allowing it in the rear.
• Distance from the main house. Scottsdale requires at least ten feet between an ADU and the main home or another ADU. This is a fire and access rule, not a setback from the lot line.
• Height. State law ties ADU height to what the underlying zoning allows for the primary home. Phoenix caps a detached ADU placed in a required yard near 15 feet, with taller heights possible through a use permit.

So the practical placement is a detached unit in the back yard, five feet off the side and rear lines, ten feet from the house, and within the city's height limit. Confirm your zoning district's exact height and yard rules before you design.

The law also limits how a city can dictate the look of your ADU. A city cannot force the ADU to match the exterior design, roof pitch, or finish of the main house. That keeps you from being pushed into an expensive custom match. It can still apply general design and lot-coverage standards, and on lots in unincorporated Maricopa County a detached ADU that sits in a required yard is held to a coverage limit within that yard area. The point is that placement is now governed by clear, statewide minimums instead of a city's discretion to say no.

Size requirements

An ADU is capped at 75% of the main home's gross floor area or 1,000 square feet, whichever is less, as the floor a city must allow. That language is identical in the city and county statutes. So if your house is 2,000 square feet, 75% would be 1,500, but the 1,000-square-foot cap wins because it is smaller. If your house is only 1,200 square feet, 75% is 900, and that lower number applies.

Cities set the rules for additional units:

• First ADU. Scottsdale limits the first ADU to 1,000 square feet or 75% of the main home, whichever is less, matching the state floor.
• Second and third ADUs. Scottsdale caps any second or third ADU at 500 square feet. Phoenix allows two ADUs on a standard lot and a third on lots of at least one acre when one unit is deed-restricted affordable.
• Lot-size limits. Phoenix also ties ADU size to lot size, with larger caps on bigger lots, up to a ceiling.

The size cap is also a budget cap. Because you are building a few hundred to a thousand square feet, an ADU costs far less than a full custom home, even though its per-square-foot price can be higher. Plan the unit around the cap, not above it.

Utility requirements

Every ADU must be a complete living unit, so it needs its own sleeping area, a bathroom, and connections to water, sewer or septic, and electricity. The state defines an ADU as a "self-contained living unit" with "its own sleeping and sanitation facilities" that "may include its own kitchen facilities." Sanitation means a real bathroom tied into the home's sewer or a septic system. A kitchen is allowed and common, but the state floor does not strictly require one.

Utilities are where the real work and cost sit:

• Water and sewer. In Phoenix or Scottsdale, the ADU ties into the same municipal water and sewer as the house, often with a new branch line. Some cities or units require a separate meter.
• Septic. On rural or unincorporated lots like Rio Verde Foothills, a second unit may need a septic expansion or a new system, since one septic field may not be sized for two homes.
• Electric. The ADU needs its own circuits and panel capacity. A backyard unit often needs a sub-panel and may need a service upgrade.
• Address and entrance. Scottsdale requires each ADU to have a separate exterior entrance and its own unique address posted near the door.

Confirm utility capacity early. A panel upgrade or septic expansion can change the whole project budget, and it is far cheaper to plan for than to discover mid-build.

Parking and rental requirements

A city cannot require extra parking for an ADU, and it cannot ban renting the unit as long-term housing. State law is direct: a government may not "require that a lot or parcel have additional parking to accommodate an accessory dwelling unit." It also may not require "a familial, marital, employment or other preexisting relationship" between the people in the main house and the people in the ADU. That means you can build a backyard casita and lease it to any long-term tenant, no relationship needed. Before the 2024 law, many Arizona cities effectively blocked this by banning second kitchens, requiring the owner to live on site, or demanding a parking pad you had no room for. The state floor swept those barriers away for covered cities and counties.

Short-term rentals are the one place owner-occupancy can apply. Scottsdale allows an ADU to be used as a vacation or short-term rental "only if the property owner physically resides at the property." So a long-term lease is open to anyone, but turning the ADU into a nightly rental can require you to live on site. Rules differ by city, so confirm the short-term rental and licensing requirements with your specific city before you plan for nightly-rental income. For everything else, the state floor gives Arizona homeowners a clear, predictable path to add one rentable unit.

The Jematell Homes approach

Setbacks, overlays, and ADU rules shape our design work from day one. Reach out and we will talk through how this applies to your specific lot and plan.

Sources

• A.R.S. 9-461.18 (Accessory dwelling units; municipalities)
• A.R.S. 11-810.01 (Accessory dwelling units; counties)
• City of Scottsdale: Accessory Dwelling Units (development standards)
• Phoenix Zoning Ordinance 706 (Accessory Uses and Structures)