ADU rules in Coalville

Detached ADUs (DADUs) are permitted uses in every zone except Light Industrial (LI): "DADU's are permitted uses in all zones, except the light industrial zone" (§03-230.D). One DADU is allowed per primary single-family dwelling, on a lot of at least 1/4 acre (10,890 sq ft) (§03-230.D.7). The §08-020 Table of Uses lists 'Dwellings, accessory' as Allowed in AG, RA, R-1, R-2, R-4, R-8, CC, and HC and Prohibited in LI. Utah's detached-ADU mandate (Utah Code 10-21-304, effective October 1, 2026) binds only a 'specified municipality' under 10-21-101(25). Coalville is a fifth-class city with an estimated 1,533 residents (Utah Population Committee, July 1, 2025), below the 5,000 threshold, so section 304 does not apply and the city's own rules govern.

Internal ADUs (IADUs: a room, basement, or area above an attached garage within the primary single-family dwelling) are permitted uses in all zones except Light Industrial (§03-230.C). One IADU is allowed per primary single-family dwelling, on a lot of at least 1/8 acre (5,445 sq ft), and it may not change the home's appearance as a single-family dwelling (§03-230.C.2, C.6). These limits fit within the closed list of conditions Utah Code 10-21-303(3) lets every city impose; state law would even let the city bar internal ADUs on lots of 6,000 sq ft or less, so Coalville's minimum is more permissive than required.

A DADU "shall not exceed one thousand (1,000) gross square feet as measured from exterior wall to exterior wall, or ⅔ the size of the primary dwelling, whichever is less" (§03-230.D.1). The IADU standards in §03-230.C list no size limit. The Chapter 2 'Dwelling, Accessory' definition repeats the 1,000 sq ft or 2/3 cap for accessory dwellings generally, but for an internal ADU in a primarily residential zone Utah Code 10-21-303(1)(b)(i) bars a city from restricting the size of the unit in relation to the primary dwelling, so that definitional cap cannot lawfully limit an IADU there. Detached ADUs 16 feet or less in height also count toward the 50 percent rear-yard coverage limit in the zone chapters.

Owner occupancy is tied to rental, not creation: renting an IADU is not allowed "if the IADU is in a primary dwelling that is not occupied as the owner's primary residence" (§03-230.C.8), and renting a DADU is not allowed "if the primary dwelling is not occupied as the owner's primary residence" (§03-230.D.9). No owner-occupancy requirement is stated for an ADU housing the owner's relatives, domestic help, or house guests. Utah Code 10-21-303(3)(j) expressly permits this rental condition for internal ADUs.

"One (1) on-site parking space shall be provided in addition to the underlying parking requirements for the primary single-family dwelling" (§03-230.C.3 for IADUs, §03-230.D.4 for DADUs). The base residential standard in the §06-050 parking table is two spaces per single-family dwelling unit. For internal ADUs this is the one added space Utah Code 10-21-303(3)(c)(i) allows; the detached-ADU parking caps in 10-21-304 do not apply to Coalville.

All ADUs, internal and detached, "shall be administratively reviewed, and approved by Staff through the building permit and/or Short-Term Rental review and approval process" (§03-230.E). Exception: where the Community Development Director foresees issues or receives community comment, the application can go to a Planning Commission public hearing with a recommendation to the City Council (§03-230.E.1), and the City Council must approve the business license for renting an ADU (§03-230.E.2). Administrative approval matches Utah Code 10-21-303(1)(a), which makes an internal ADU a permitted use in any area zoned primarily for residential use.

Both ADU types may be rented long term, but the owner must obtain a business license (§03-230.C.5, §03-230.D.6), approved by the City Council (§03-230.E.2), and must occupy the primary dwelling as their primary residence (§03-230.C.8, §03-230.D.9). Renting a DADU for less than 30 days "shall not be permitted" (§03-230.D.8). Renting an IADU for less than 30 consecutive days requires a Short-Term Rental Permit under §03-220 (§03-230.C.7, §03-230.E.3). Section 03-220 is in tension with that allowance: its definitions say an ADU "must be rented more than thirty (30) days" and that a short-term rental "cannot be a detached unit", it treats owner-occupied accessory apartments as Room Rentals, and it caps short-term rentals at 5% of primary households citywide with no more than three within a 500-foot radius in residential and agricultural zones (§03-220.B, C.9.f, C.13).