ADU rules in American Fork

Ord. 2026-09-21 (adopted 9-22-2026) created Sec 17.5.136, which permits a detached ADU on any lot or parcel that contains at least 11,000 square feet, contains a detached single-family dwelling, and is located where the single-family dwelling is a permitted use. The section also states that nothing in it authorizes a detached ADU on a lot smaller than 11,000 square feet, so smaller lots still cannot have one. The owner of a legally constructed accessory structure may apply to convert it to a detached ADU if it meets setback and building, health, and fire codes. The ordinance implements Utah Code 10-21-304 (in force 10-1-2026), which requires cities like American Fork to permit detached ADUs on single-family lots of 11,000 square feet or larger. The older Sec 17.5.106 (living and sleeping quarters not permitted in any accessory building) remains in the code; it continues to govern ordinary accessory buildings that are not detached ADUs.

One accessory apartment is allowed within a single-family home in all single-family residential zones under Sec 17.5.134, and the residential zone chapters list accessory apartments as a permitted use. The unit must have its own eating, sleeping, and sanitation areas, a dedicated entrance on a side or rear (front only if below grade), and interior access to the main living area, and it is not allowed in any multi-family dwelling. Since Ord. 2026-09-21, a lot may hold no more than one accessory dwelling unit, whether attached, internal, or detached, so a home with an accessory apartment cannot also add a detached ADU.

Sec 17.5.136(F)(3) says the footprint of a detached ADU shall not be greater than 1,500 square feet and shall not exceed the footprint of the primary residential structure on the site. A detached ADU is also limited to 24 feet in height and may not be taller than the house, and the detached ADU plus any other accessory structures may not exceed 25% of the rear yard open space. Sec 17.5.134 sets no square footage limit for an accessory apartment inside the home; the practical limit is that it must fit within the existing house without changing its outside appearance.

For an accessory apartment, Sec 17.5.134 says no accessory apartment shall be created or occupied unless the property owner occupies either the main dwelling or the apartment, meaning full time residency by the bona fide owner(s) shown on the Utah County tax rolls. For a detached ADU, Sec 17.5.136(H) says the owner of the lot shall reside in either the detached single-family dwelling or the detached accessory dwelling unit. Either way the owner may live in the main house or the ADU.

Sec 17.5.136(G) requires each detached ADU to provide two on-site parking spaces if it is 650 square feet or larger, or one if it is smaller, and garage spaces lost when a detached garage is converted must be replaced on site; this matches the ceiling in Utah Code 10-21-304(3)(b)-(c). For an accessory apartment inside the home, Sec 17.5.134(B)(4) still requires two off-street spaces in addition to the two required for the house, tandem driveway parking counts, spaces may not sit in a front or side yard except within an approved driveway, and a lot that cannot meet the requirement cannot have an apartment. That two-space rule appears to exceed state law for internal ADUs: Utah Code 10-21-303(3)(c)(i) lets a city require a home 'to include one additional on-site parking space for an internal accessory dwelling unit', so confirm with the city before planning around the second space.

Sec 17.5.134 states accessory apartments are permitted within the city subject to its conditions, and the residential zone chapters (for example R-1-9000, §17.4.204) list accessory apartments under permitted uses. For detached ADUs, Sec 17.5.136(L) provides that applications are reviewed administratively by the Development Review Committee for compliance with objective standards, and Sec 17.5.136(B)(2) says a qualifying detached ADU 'shall not require a conditional use permit when located in a primarily residential zone', as Utah Code 10-21-304(3)(a) requires. Building permits and the adopted fee schedule still apply.

The signed Ord. 2026-09-21 says a detached ADU 'shall not be rented, leased, offered, or otherwise occupied as a rental for a period of less than ninety (90) consecutive days', and a rented property must be registered in the city's Landlord Registry and hold a business license (the online code misprints this as 'not less than'; the signed ordinance governs). For an accessory apartment, Sec 17.5.134 says it shall not be intended for sale or detached by deed and shall only be rented, and limits occupants to one person, a related household plus no more than two unrelated persons, or up to four unrelated individuals. Ord. 2019-05-29 removed the apartment section's own short-term rental clause; rentals under 30 days are now governed citywide by Chapter 17.18, which requires the property to be owner-occupied, bars stays shorter than two consecutive nights, and requires a Chapter 5.42 short-term rental business license. Under Sec 5.24.010, compliant owner-occupied accessory apartments in R-1 zones occupied by relatives or no more than four unrelated people are exempt from landlord registration.