ADU rules in Cottonwood Heights

Chapter 19.75 still lists detached ADUs as conditional uses in the R-1 (single-family), RR-1 (rural residential) and F-1 (foothill residential) zones, approved by the Planning Commission after a public hearing (§19.75.030: "Detached ADUs may be allowed as conditional uses"). Since October 1, 2026, Utah Code 10-21-304 requires Cottonwood Heights (population 34,238, a third-class city and so a "specified municipality") to adopt rules permitting a detached ADU on any single-family lot of 11,000 sq ft or more, but the statute directs the city to adopt that rule rather than granting the right itself, and the city had not amended its code as of October 21, 2026. A city-initiated amendment (ZTA-26-004) that would make detached ADUs a permitted use went to a Planning Commission public hearing on October 21, 2026 and still needs City Council adoption. Today a detached ADU must be a permanent structure in the rear yard, at least 6 feet from the house, and meet the zone's accessory building standards.

Internal ADUs are permitted uses in the R-1, RR-1 and F-1 zones on owner-occupied lots larger than 6,000 sq ft; they are prohibited on lots of 6,000 sq ft or less or where the house is served by a failing septic tank (§19.75.030). An internal ADU must be created within the footprint of the house as it exists at the time and must not change its single-family appearance, which matches the internal-ADU rules of Utah Code 10-21-303. It needs an ADU permit, inspection and notarized affidavit, renewed annually.

The ADU chapter sets no square-footage cap: an internal ADU must fit within the footprint of the existing house (§19.75.020), and a detached ADU "shall meet all accessory building standards for height, lot coverage, rear-yard coverage, size" for its zone (§19.75.050(L)(4)). Those standards say accessory buildings may not cover more than 25% of the rear yard and, "in any residential zone except a rural residential zone," may not have "a floor area greater than 70% of the floor area of the primary structure" (§19.76.030). Accessory buildings are generally capped at 20 feet in height, with an extra foot of setback for each foot over 14 feet. Utah Code 10-21-304(4) lets cities regulate detached ADU size, height and lot coverage, so these limits survive the 2026 state law.

The record owner must occupy either the house or the ADU as a permanent residence and may never receive rent for the owner-occupied unit (§19.75.050(A)); owner occupancy means legal residence at the site at least 200 days per calendar year (§19.75.020). It is proven by a notarized affidavit (§19.75.060), and the ADU must be vacated if the owner no longer lives there or the property changes hands without a new ADU application (§19.75.090). Utah Code 10-21-304(4)(c) expressly lets cities keep this requirement for detached ADUs.

"Each detached ADU shall require two off-street parking spaces in addition to required parking for the primary dwelling unit," and an internal ADU requires one more space with at least three on the lot (§19.75.050(F), (G)). Tandem parking is prohibited for the added spaces, new front-yard parking is barred for detached ADUs, and garage or carport spaces lost to an internal ADU must be replaced. Utah Code 10-21-304(3) now bars requiring more than one space for a detached ADU under 650 sq ft (two at 650 sq ft or more), and 10-20-618(4)(b) bars a specified municipality from refusing to count an unobstructed tandem space as two spaces, so parts of the city rule conflict with state law until the code is amended. The pending amendment ZTA-26-004 would require one space for each ADU.

Internal ADUs are permitted uses that still require an ADU application, fees, inspection, affidavit, any building permits and annual renewal (§19.75.040(A)). Detached ADUs remain conditional uses requiring Planning Commission approval after a public hearing (§19.75.040(B)); the city's ADU page lists a $1,100 conditional use permit fee on top of the $100 ADU license. Utah Code 10-21-304(3)(a), in force since October 1, 2026, bars a conditional use permit for a detached ADU in a primarily residential zone, and the pending amendment ZTA-26-004 would make both types permitted uses, but until the City Council adopts it the codified conditional use process is the city's written rule.

"ADUs shall not be used as short-term rentals" (§19.75.050(B)); a short-term rental is any rental for fewer than 30 consecutive days (§19.75.020), and an internal ADU is defined as created for long-term rental of 30 consecutive days or longer. The owner may never receive rent for the unit the owner occupies (§19.75.050(A)).