Building an ADU (casita) in Tempe

What you can build in Tempe

Arizona's 2024 ADU law, HB 2720, required cities of 75,000 or more to allow ADUs on lots where single-family homes are allowed. Tempe adopted Ordinance O2024.51 in November 2024. Its ADU rules are in Zoning and Development Code Section 3-402, which says state law controls if the two conflict. See our Arizona ADU law page.

ADUs are permitted in all residential districts when the lot contains a single-family home:

• One attached and one detached ADU on a lot under one acre.
• One more ADU on a lot of one acre or more, if one of the ADUs is a restricted-affordable unit. That unit must be deed-restricted and rented only to households earning up to 80% of area median income, with an annual report to the city.
• Lots that already have a duplex, triplex or similar aren't eligible.

Each ADU must have its own sleeping and sanitation facilities (shower or tub, toilet and sink) and a kitchen. Prefab and modular units, tiny homes on a permanent foundation, and units built on trailers with the axles removed and the chassis fixed to a foundation are allowed if they meet the building code. See our backyard tiny house guide and prefab ADU guide. [1][2][3]

Size, height and setbacks

Size. On a lot under one acre, an ADU can be 75% of the main home's gross floor area or 1,000 square feet, whichever is less. On a lot of an acre or more, the cap is 75% or 2,000 square feet. Gross floor area means interior habitable area, not garages, carports or exterior storage. If you convert part of your house, only the rest of the house counts toward the 75%. The city's example: a 1,200 sq ft house allows a 900 sq ft ADU. An ADU under the 1,000 sq ft cap can have up to three bedrooms.

Lot coverage. Every ADU counts toward your district's lot coverage limit, along with the house and other enclosed buildings. Open patios, canopies and awnings don't count. In the city's R1-6 example, the limit is 45%.

Setbacks. The rear, side and street side setback is at least 5 feet, unless the district, an overlay or the accessory-building rules allow less. Next to a public alley, side and rear setbacks are measured from the middle of the alley. ADUs can't go in the front building setback.

Height. Tempe's code says ADUs "are subject to the same height regulations that apply to the zoning district with a single-family dwelling on the same lot," and the city's ADU page puts that at typically 30 feet. The same code section also points to the accessory-building rules (Section 3-401), which cap accessory buildings at 15 feet unless a use permit allows more, and to Section 3-420 on second-story additions.

Tempe's ADU page also says that "based on the December 17, 2025 Board of Adjustment decision," the city "requires a Use Permit for two-story ADU designs." Section 3-420, as amended June 4, 2026, requires a use permit for second stories on one-story homes and lists exceptions that mention two-story ADUs.

Arizona law (ARS 9-461.18) says a city must allow ADUs as a "permitted use," which it defines as approval without "a public hearing, variance, conditional use permit, special permit or special exception." It also bars ADU height rules "more restrictive than those for single-family dwellings within the same zoning area." If you want a two-story or taller detached ADU, confirm with the Planning Division which rules apply before you design. [1][2][3][4]

Parking and garage conversions

Tempe requires no additional parking for an ADU. You may add parking if you want; a space off an alley needs a 23-foot backing distance.

But if your ADU removes or changes a required parking space for the main home, such as when you convert a garage or carport, you must replace that space where the Community Development Director allows. Putting it in the front or street side setback takes a use permit. Arizona law says a city may not "require that a lot or parcel have additional parking to accommodate an accessory dwelling unit." Before you plan a garage conversion, confirm with the Planning Division at (480) 350-4311 how Tempe applies its replacement rule. See our garage conversion guide.

An existing, legally built guest quarters can be converted to a rentable ADU with building permits, even if it is larger than the ADU size cap. [1][2][3][4]

Design and HOAs

Tempe can't require your ADU to match the main home's exterior design. But HOA covenants (CC&Rs) can be stricter than city rules and may restrict an ADU or renting it, even where the city allows it. The city notes that most Tempe subdivisions don't have HOAs or CC&Rs. If yours does, check whether its architectural review committee must approve your plans. [2][3]

Fees, utilities and timeline

Tempe's ADU sources don't list ADU-specific fees. Building permit invoices are paid through the Tempe Citizen Access Portal; ask the Permit Center about fees for your project. For budgeting, see our ADU cost guide.

Water, sewer and utility connections must meet city standards. For whether the ADU can have its own meters or a submeter, the city says to check with your utility providers. Tempe's Municipal Utilities Division has said existing water and sewer infrastructure can handle the added demand from ADUs.

Tempe doesn't publish a set review time for ADUs. All submittals are electronic, and a permit may be issued once Plan Review finds the documents comply. See our ADU permit process guide. [1][2][5][6]

Renting your ADU

You can rent your ADU long term. Arizona law bars Tempe from stopping you from renting the house and the ADU separately on leases of 90 days or more, or requiring the tenant to be related to you. ADUs must also meet the Tempe City Code's rental housing rules, in Chapter 21, Article II. An ADU in the Section 8 voucher program must meet HUD's criteria.

Short-term rentals. Renting for 29 days or less needs a Tempe Short-Term Rental License for each unit, before you list it. The annual fee is $250 per property, or $187.50 if issued July 1 or later. You need a transaction privilege tax license, Maricopa County Assessor rental registration, and proof of at least $500,000 in liability coverage, and you must notify your neighbors. If your ADU was built on or after December 20, 2024, Tempe requires you to live on the property to rent it as a licensed short-term rental.

An ADU can't be split onto its own lot or sold separately from the lot. [1][2][4][7]

Standard plans

Tempe's ADU and Single-Family Standard Plan Library collects pre-reviewed plans for detached ADUs. You pick a design, license it from the designer, and then submit for building permits. Standard plans can't be significantly changed, for example by moving doors and windows or changing the floor plan, without a full plan review.

The city also picked ten winning designs in the 2025 AARP ADU Design Challenge. They can't be licensed until each designer completes standard plan review. Tempe says that as of July 1, 2026 it is required to allow submittals for ADU standard plans, under the state's pre-approved plan law. [2][8][9]

Permit steps in Tempe

1. Check eligibility

   Your lot must have an existing single-family home in a zone that allows residential uses. Find your zone on Tempe's zoning map and check any HOA rules or CC&Rs, which may restrict an ADU or renting it. An existing guest quarters counts toward your ADU total. [2][3]

2. Work out size, lot coverage and setbacks

   Multiply your home's interior habitable area by 0.75 and cap it at 1,000 square feet (2,000 on lots of an acre or more). Add up the footprints of all enclosed buildings, including the ADU, and compare with your district's lot coverage limit in ZDC Section 4-202. [1][3]

3. Design the ADU or license a standard plan

   Hire a designer, or license a pre-reviewed plan from Tempe's ADU and Single-Family Standard Plan Library by contacting its designer. [8]

4. Ask about grading and drainage

   Grading and drainage needs depend on your site and the scope of work. Email the Permit Center at PermitCenter@tempe.gov or call 480-350-4311. [2][3]

5. Apply online

   Submit a site plan, a floor plan that includes the existing home, and construction documents through the Tempe Citizen Access Portal. All submittals are electronic, and you need a registered account. [3][5][6]

6. Plan review, fees and permit

   Plan Review checks the construction documents against Tempe's codes, and a permit may be issued once they comply. Invoices and payments go through the Citizen Access Portal. [5][6]

7. Build, address and inspect

   Each ADU needs its own address posted near its main entrance, with numbers or letters of at least 4 inches in a contrasting color (for example 1234 A, 1234 B). Schedule inspections with Building Safety as you build. [1][3][10]

Pre-approved and sample plans

• ADU and Single-Family Standard Plan Library

  Pre-reviewed standard plans for detached ADUs and single-family homes that you license from the designer and submit for a building permit. [8]

• 2025 AARP ADU Design Challenge winners

  Ten winning ADU designs selected by the city; they can't be licensed until each designer finishes the standard plan review. [2]

Who to call

• Community Development, Planning Division

  ADU zoning and planning questions: Planning@tempe.gov

  (480) 350-4311

  [2][3]

• Permit Center, Building Safety Division

  Building permits, grading and drainage, submittals and payments: permitcenter@tempe.gov

  480-350-4311

  31 E. Fifth St., Garden Level East, Tempe, AZ 85281 (Monday to Friday, 8 a.m. to 5 p.m.)

  [5][10]

• Tempe Tax and License

  Short-term rental licenses: license@tempe.gov

  480-350-2955

  20 E. 6th Street, Third Floor, Tempe, AZ 85281

  [7]

Questions people ask