ADU rules in Tempe

One attached and one detached ADU are allowed on any lot under one acre that contains a single-family dwelling, in every residential district. On a lot of one acre or more, one additional ADU (a third unit) is allowed if at least one ADU on the lot is a deed-restricted affordable unit.

One attached ADU is allowed per lot alongside one detached ADU, in all residential districts where the property contains a single-family dwelling. An existing guest quarters counts toward the one attached or one detached allowance.

Gross floor area means interior habitable area, excluding garages, carports, and exterior storage. An ADU capped at 1,000 sq ft may have at most three bedrooms; there is no bedroom limit on lots of one acre or more. A guest quarters converted to an ADU may exceed the size cap.

Tempe's ADU section imposes no owner-occupancy requirement for building an ADU or renting either unit long term. The one exception is short-term or vacation rental: under City Code Section 16A-213(k) (as amended by Ord. O2026.01, adopted January 8, 2026), the owner of a short-term or vacation rental must live on the property if it contains an ADU whose certificate of occupancy, certificate of completion, or similar final approval was issued on or after September 14, 2024; ADUs finalized on or before September 13, 2024 are exempt. The city's ADU FAQ still gives the older December 20, 2024 cutoff, but the code text governs.

The owner may add parking voluntarily. If ADU construction removes or modifies a required parking space for the main residence, that space must be replaced in a location authorized by the Community Development Director.

ADUs are a permissible use in all residential districts when the property contains a single-family dwelling, approved through a standard building permit and subject to building, fire, and health codes. Exception: a two-story ADU next to a single-story house needs a discretionary Use Permit under ZDC Section 3-420, which the Board of Adjustment confirmed on December 17, 2025 when it overturned a zoning administrator opinion that no Use Permit was needed (case PL250363, 6-1 vote); Ord. O2026.23 (June 4, 2026) exempts properties whose house is already two stories. The city also runs a Standard Plan Library of pre-reviewed detached ADU plans that owners can license and submit for a building permit.

A third ADU on a lot of one acre or more must be deed-restricted affordable, rented only to households at or below 80% of area median income, with annual compliance reports to the city. Short-term rentals also need neighbor notification, an emergency contact, and liability insurance under the licensing article.