Accessory Dwelling Unit (ADU) Rules for Mammoth, AZ

ADU State Law

What can you build in Arizona?

• –ADUs must be allowed as a permitted use wherever single-family dwellings are allowed.
• –Must allow at least 2 ADUs per lot (1 attached + 1 detached). A third detached ADU must be allowed if the lot is ≥ 1 acre and one ADU is restricted-affordable (≤ 80% Area Median Income).
• –ADU rules cannot be more restrictive than single-family rules in the same zoning area for height, setbacks, lot size, lot coverage, and building frontage; and side/rear setbacks cannot exceed 5 feet.
• –The city cannot require additional parking (or fees in lieu of parking).
• –The city cannot prohibit separately leased long-term rentals (≥ 90 days or month-to-month) for either the primary home or the ADU; local short-term rental rules may still apply.
• –The city cannot require the ADU to match exterior design, roof pitch, or finishing materials of the primary home.
• –The city cannot require public street improvements as a condition of allowing an ADU, except to repair or reconstruct a street disturbed by ADU construction.
• –The city cannot require a restrictive covenant as a condition of approving an ADU.
• –ADUs cannot be built over a public utility easement without written utility consent; building, fire, and health codes still apply, but the city cannot require commercial code or sprinklers solely because it is an ADU.
• –Private restrictions may still apply (HOAs, deed restrictions, and other private covenants between parties).
• –Backstop rule: If the municipality failed to adopt the required ADU regulations by January 1, 2025, ADUs are allowed on residential lots in that municipality without limits.
• –In municipalities with population ≤ 75,000, in unincorporated county areas, and on the statute's exempt lands (tribal; defined military vicinity; defined airport vicinity with >65 dB), there is no state ADU override. ADUs depend on local rules.
• –Private deed restrictions and HOA covenants may still limit ADUs, and the statute does not eliminate those private covenants (it mainly limits what a municipality can require or condition).