ADU rules in Mesa

One detached ADU is permitted per lot in any Agricultural, Residential, Commercial and Mixed Use, or Downtown district where a Single Residence is allowed, and on any lot whose principal use is an existing Single Residence even outside those districts. ADUs are listed as P (permitted) in the district use tables. Ord. 6025 (effective 8-26-2026) reworded the second route to require the existing Single Residence to be the principal use.

One attached ADU is permitted per lot under the same applicability rules as detached ADUs. The ADU must have a separate and independent entrance and may not have an internal connection to the primary residence.

Habitable area excludes unconditioned storage and parking space. No minimum lot size to establish an ADU.

Section 11-31-3 (read in full, including the Ord. 6025 amendments) contains no owner-occupancy requirement, and A.R.S. 9-461.18(B)(2) prohibits Mesa from requiring any preexisting relationship between the occupants of the primary dwelling and the ADU.

The city's ADU FAQ adds that the property must still maintain at least two parking spaces for the primary residence. A.R.S. 9-461.18(B)(3) bars ADU parking requirements or in-lieu fees.

ADUs are a permitted (P) accessory use in the district land use tables, subject to the standards of Section 11-31-3; only a building permit is required per the city's ADU page (Historic District properties also need a Certificate of Appropriateness). The city also runs a Preapproved Housing Design Plan Program whose Class 4 covers ADU plans of 200, 600 or 1,000 sq ft; approved plans are posted in its Standard Plan Library and used under a license from the plan owner.

Ord. 6025 (adopted 7-27-2026, effective 8-26-2026) added 11-31-3(B)(7), 'ADUS MAY NOT BE USED AS A BOARDING HOUSE,' and the same sentence to the Boarding House definition in 11-86-2, which covers a dwelling for five or more unrelated individuals where rent is charged separately for individual rooms. The city ADU FAQ confirms ADUs may be used as short-term rentals with a license, and Mesa's STR chapter has not adopted the optional owner-residency condition that A.R.S. 9-500.39(B)(9) allows for properties with ADUs approved after 9-14-2024. An ADU may not be sold separately from the primary residence. The second detached ADU allowed on 1+ acre lots requires at least one ADU on the lot to be a restricted-affordable unit rented to households earning up to 80% of area median income.