ADU rules in Midvale

External accessory dwelling units (EADUs, defined in §17-2-5 as an ADU on the same lot as a primary dwelling and detached from the principal building) carry an X in the Allowed column of the SF-1, SF-2, RM-12 and RM-25 residential use tables, and are also Allowed in the Mixed-Use, State Street, Transit-Oriented Development, Bingham Junction, Riverwalk and State Street Overlay zone tables. An EADU may only be built on a lot with one detached single-family dwelling, on a lot larger than 6,000 sq ft, not on the same lot as a mobile or manufactured home, and only one EADU per property. Utah Code 10-21-304 (in force since October 1, 2026) requires a specified municipality such as Midvale (population over 37,000, a third-class city) to permit a detached ADU on single-family lots of 11,000 sq ft or more; Midvale's existing code already allows them on smaller lots, so no local change was needed and none had been adopted as of the October 20, 2026 council agenda.

Internal accessory dwelling units (IADUs) carry an X in the Allowed column of the same residential use tables, subject to the same conditions: one detached single-family dwelling on the lot, a lot larger than 6,000 sq ft, not within a mobile or manufactured home, and one IADU per property. Midvale defines an IADU by reference to state law, under which it is a unit created within a primary dwelling and within that dwelling's footprint at the time it is created; the code has no separate category for a unit in a newly attached addition, though §17-7-1.2.1(E)(4) requires any addition to meet the zone's development standards. The codified definition in §17-2-9 still cites the renumbered Utah Code 10-9a-530; Ordinance 2026-O-26 (adopted September 1, 2026, not yet codified) re-points it to 10-21-101.

The cumulative maximum building area of all unoccupied accessory structures and an EADU is the larger of 900 sq ft or 13% of the lot area, so an existing shed or detached garage reduces what is left for the EADU. An EADU may not exceed 20 ft in height with a pitched roof or 16 ft with a flat roof, and may be one to one and one-half stories. No floor-area cap applies to internal ADUs; state law (Utah Code 10-21-303(1)(b)) bars cities from limiting an internal ADU's size relative to the primary dwelling.

The property owner must occupy one of the dwelling units on the property (the house or the ADU) as their permanent residence for as long as the EADU or IADU remains, and must record a notice against the property title describing the ADU before a certificate of occupancy is issued. State law expressly lets cities impose this for detached ADUs (Utah Code 10-21-304(4)(c)).

Table 17-7-1.7 requires 1 off-street parking space per IADU or EADU, in addition to the 2 improved off-street spaces every residential lot must provide under §17-7-1.7(A); the same 1-space row appears in the SF-2, RM-12 and RM-25 parking tables. This is within state limits: Utah Code 10-21-304(3) bars requiring more than one space for a detached ADU under 650 sq ft (two for 650 sq ft or larger), and 10-21-303(3)(c) allows one added space for an internal ADU.

Both EADUs and IADUs carry an X in the Allowed column (not Administrative or Conditional) of every use table that lists them, subject to the use-specific criteria in §17-7-1.2.1 and its counterparts in each zone chapter. A building permit is required before construction. This matches Utah Code 10-21-304(3)(a), which bars a conditional use permit for a detached ADU in a primarily residential zone.

An EADU or IADU may not be rented or leased for a period of less than thirty consecutive days, which rules out short-term rental of either ADU type. State law allows this floor for internal ADUs (Utah Code 10-21-303(3)(i)) and would allow up to a 90-day floor for detached ADUs (10-21-304(4)(b)).