How do I get a permit to build an ADU in Arizona?

You get an ADU permit from the city, town or county that controls your lot, not from the state. In Arizona cities of more than 75,000 people, and in every county since January 1, 2026, an ADU (accessory dwelling unit) is a permitted use on a single-family lot. That means no public hearing, variance or special use permit is needed for the unit itself. You still need a building permit: you check your lot against the local ADU rules, submit a site plan and construction plans, pay the fees, pass plan review, and then pass inspections before anyone moves in. Scottsdale adds a pre-application and an administrative approval before plan review. Smaller towns such as Cave Creek, Carefree and Fountain Hills write their own rules.

Below is who issues the permit, what to check before you draw anything, how the process runs in Phoenix, Scottsdale and unincorporated Maricopa County, and what happens after the permit is issued.

Who issues an ADU permit in Arizona

The permit comes from whoever has zoning power over your parcel. Two state laws set the floor those offices must follow:

• Cities over 75,000 people. Under A.R.S. 9-461.18, a covered city must allow at least one attached and one detached ADU on any lot where a single-family home is allowed. Phoenix, Scottsdale and Mesa are covered.
• Counties. A.R.S. 11-810.01 puts the same floor on every Arizona county from January 1, 2026. That covers unincorporated land such as the Rio Verde Foothills, which Maricopa County permits.
• Smaller towns. Towns under the 75,000 line are not covered by the city law and are not county land, so their own zoning decides. See whether Cave Creek, Fountain Hills and Carefree allow casitas and ADUs.

The phrase that matters is "permitted use." The city statute defines it as "the ability for a development to be approved without requiring a public hearing, variance, conditional use permit, special permit or special exception." In plain terms, if your unit meets the written rules, the city cannot turn it down because a neighbor objects. It reviews your plans against code, the same way it reviews a new home. For what the 2024 and 2025 laws changed, see what HB 2720 changed for ADUs.

Check your lot before you draw plans

Most ADU permit problems start on the lot, not in plan review. Before you pay for design, confirm these:

• Zoning district. Your district sets the setbacks and lot coverage the ADU must fit inside. Phoenix points owners to its My Community Map to find the district.
• Size cap. State law sets the floor at 75% of the main home's floor area or 1,000 square feet, whichever is less. Cities can allow more. Phoenix raises the cap on lots over 10,000 square feet. The numbers for each city are in our ADU setback and size rules by city.
• Lot coverage. Phoenix's ADU guide has you add up the house, garages, covered patios and every shed or ramada, then compare the total to what your district allows under roof. An ADU must fit in what is left.
• Easements. Under the city statute, an ADU "may not be built on top of a current or planned public utility easement" unless the utility gives written consent. Check your plat before you pick a spot.
• Unpermitted structures. Phoenix asks owners with unpermitted buildings on the lot to legalize them before pursuing the ADU permit.
• HOA rules. The state law limits cities and counties, not private covenants. Read your HOA's rules first. See whether an HOA can block an ADU the city allows.

What plans you submit

An ADU permit needs the same kind of plan set as a small house. Expect to provide:

• A site plan drawn to scale, showing the lot lines, the main home, the ADU, setbacks, and the utility routes. Phoenix states the site plan and floor plan "must be drawn to scale to be used for permit approval."
• Floor plans and elevations of the unit.
• Construction documents: structural, energy, plumbing, mechanical and electrical details to the building code your city has adopted.

Building and fire codes still apply to an ADU. The city statute does not override them, with two limits: a city "may not require an accessory dwelling unit to comply with a commercial building code or contain a fire sprinkler." The county statute carries the same limit.

Phoenix is building a shortcut. Its ADU Standard Plan Library, from the 2024 design competition with AIA Phoenix Metro, will offer pre-approved detached ADU plans free to city residents. The plans must be submitted as drawn, and a plot or site plan is still required. When we last read the city's page, the first four plans were still in review.

How the process runs in Phoenix, Scottsdale and Maricopa County

Phoenix. The ADU goes through the city's residential permit process with a site plan and construction plans, like an addition. Questions about whether an ADU fits a lot go to the Planning and Development Department's site planning team. A garage or carport conversion has one extra step: Phoenix requires new off-street parking spaces in dustproof condition, and they cannot sit in the front yard setback.

Scottsdale. Scottsdale runs a multi-step process, set out on the city's ADU page:

1. Pre-application. Submit a pre-application request online, with any site plan, building elevations and utility information you have.
2. Pre-application meeting. City staff meet with you to go over the requirements for your unit.
3. Formal administrative application. Staff tell you how to apply for administrative review and may ask for more information.
4. Permit review. Only after administrative approval do you submit construction documents and plans for permit review. The permit issues once every code requirement is met.

Scottsdale also requires each ADU to have a separate entrance and its own address, and its utilities must be separately metered from the main home. A Scottsdale guest house, by contrast, shares utilities and cannot be rented on its own, and it skips the administrative step. Our page on Scottsdale's ADU and casita rules covers the size and spacing limits.

Unincorporated Maricopa County. The county takes residential permits online through its Permit Center. You need an account, a site plan, a lot coverage figure and the documents the application lists, and you pay any upfront fees when you apply. Two county rules matter on rural land. A third detached ADU on a lot of one acre or more needs a deed restriction recorded with the County Recorder before that permit is issued, and the restricted unit may only be rented to households earning no more than 80% of the area median income. And where the ADU will not be on sewer, the county may require the septic system serving it to be sized for it before construction.

How big an ADU the permit can cover

The permit covers a unit only as large as your city or county allows. The state floor is the same everywhere it applies: a city or county must allow an ADU of 75% of the main home's gross floor area or 1,000 square feet, whichever is less. Above that floor, each place sets its own cap:

• Phoenix. On lots up to 10,000 square feet, an ADU caps at 1,000 square feet or 75% of the main home, whichever is less. On larger lots the cap is 3,000 square feet, 10% of the net lot area, or 75% of the main home, whichever is least.
• Scottsdale. The first ADU caps at 1,000 square feet or 75% of the main home, whichever is less. Any other ADU on the lot caps at 500 square feet.
• Unincorporated Maricopa County. The county must allow at least the state floor, with one attached and one detached ADU, and a third detached unit on a lot of one acre or more.

Size the unit to the cap before design starts. A plan drawn even a little over the limit comes back from review, and redrawing it costs weeks.

Do you have to live on the property to get the permit?

Not to build one in a covered city. The city statute says a city may not require "a familial, marital, employment or other preexisting relationship" between the owner and the ADU's occupant, and it may not ban leasing the house or the ADU as separate long-term rentals. Scottsdale adds a condition on renting: its ADU guide says an ADU can be a vacation or short-term rental "only if the property owner physically resides at the property," and the city's ordinance applies the same owner-on-site rule to any ADU that is rented. Rental rules change often, so read your city's current rule before you plan around rental income. Our page on renting a casita or ADU in Scottsdale covers that city in detail.

Who pulls the permit: you or a licensed contractor

Most ADUs are permitted by the licensed contractor who builds them. An owner can pull the permit under Arizona's owner-builder exemption, A.R.S. 32-1121, but that exemption covers work intended for occupancy solely by the owner and not offered for sale or for rent. An ADU you plan to lease does not fit that description, so a rental unit usually needs a licensed contractor. Check the contractor's license with the Registrar of Contractors before you sign.

Review, inspections and the final sign-off

Plan review is where the calendar goes. For the whole plan review and permitting phase, allow 2 to 4 months, depending on jurisdiction. Published city targets cover a single review pass: Scottsdale, for example, targets 7 business days for its administrative check and 15 business days for substantive review on a standard residential plan set. Intake, each round of corrections and any other required approval add to that. Our page on how long a building permit takes in Arizona breaks down the review clocks, and how long it takes to build an ADU covers the whole project.

Once the permit issues, the unit is inspected at each stage, from footings through framing, rough plumbing and electrical, insulation and final. Nobody should live in the unit until it passes its final inspection. Keep the permit and the final approval with your records, since a buyer, an appraiser or a lender will ask for them. An ADU built without a permit is a real problem later; see what happens if you build without a permit.

Fees, forms and review times change. Confirm the current steps with your city, town or county before you submit.

Building an ADU with Jematell Homes

We design and build casitas, guest houses and ADUs across the Phoenix metro, with a new home or on a lot you already own, and we handle the permits, engineering and inspections. Licensed under Arizona ROC# 339367. Send us your lot's address through our contact page and we will tell you which rules apply to it.

Sources

• A.R.S. 9-461.18 (Accessory dwelling units; municipalities)
• A.R.S. 11-810.01 (Accessory dwelling units; counties)
• City of Phoenix: Accessory Dwelling Units and the ADU Standard Plan Library
• City of Phoenix: Beginner's Guide to ADUs
• City of Scottsdale: Accessory Dwelling Units (application process)
• Maricopa County: Residential Construction permits
• Maricopa County Directive DD-3016-01: Restricted-Affordable ADUs