ADU rules in Syracuse

Syracuse's code expressly allows detached ADUs, but only in the A-1, R-1, R-2, R-3, and RPC zones, only on a lot with an existing (or concurrently built) single-family dwelling, only on lots of at least 10,000 square feet, and only with a minor conditional use permit. State law now goes further: since October 1, 2026, Utah Code 10-21-304(1)(a) says a specified municipality such as Syracuse "A specified municipality shall adopt a land use regulation that permits a detached accessory dwelling unit on any lot or parcel that is 11,000 square feet or larger and contains a single-family dwelling, if the single-family dwelling is a permitted use on the lot or parcel", and 304(3)(a) bars requiring a conditional use permit for a detached ADU in a primarily residential zone. As of October 21, 2026 the city had not amended its ADU section to match (no Planning Commission hearing or Council ordinance on ADUs since June 2026), so the local zone list and permit step are still the text on the books, but a homeowner on an 11,000+ sq ft single-family lot outside the listed zones (for example R-4) can point to the statute.

Internal (basement or attic) and attached ADUs are expressly allowed, but only in the A-1, R-1, R-2, R-3, and RPC zones on single-family lots meeting the underlying zone's minimum lot size, and the code requires a minor conditional use permit. For internal ADUs, Utah Code 10-21-303(1)(a) makes the use "a permitted use" in any area zoned primarily for residential use, and a city may prohibit one only on the grounds the statute lists (for example a lot of 6,000 sq ft or less), so the local zone list and permit requirement are narrower than state law allows for units built inside the house. Attached additions built outside the house's existing footprint are not internal ADUs under Utah Code 10-21-101(16), which requires a unit created "within the footprint of the primary dwelling", so they remain governed by the local rules.

Internal and attached ADUs may not exceed 50 percent of the gross square footage of the principal dwelling; detached ADUs may not exceed the footprint of the main dwelling or 1,500 square feet of gross living area, whichever is smaller. Minimum size is whatever the adopted building code requires. The detached cap is the kind of size limit Utah Code 10-21-304(4) lets a city keep, but for internal ADUs Utah Code 10-21-303(1)(b)(i) says a city may not restrict "the size of the internal accessory dwelling unit in relation to the primary dwelling", so the 50 percent cap should not be enforceable against a unit built entirely inside the house.

An owner occupant must live on the property, in either the principal dwelling or the ADU, and a deed restriction recording that requirement must be filed with the county recorder before a building permit issues. Exceptions: a bona fide temporary absence of three years or less (military service, temporary job assignment, sabbatical, voluntary service) or the owner's placement in a hospital, nursing home, or assisted living facility. Utah Code 10-21-304(4)(c) expressly allows this owner-residency rule for detached ADUs.

The code requires one added on-site, off-street space for an internal ADU or a studio or one-bedroom attached or detached unit (tandem not allowed), and two added spaces for an attached or detached unit with two or more bedrooms (tandem allowed); the ADU's parking must be independent of the primary household's parking. Since October 1, 2026, Utah Code 10-21-304(3)(b)-(c) bars requiring more than two spaces for a detached ADU of 650 sq ft or more and more than one space for a detached ADU "that is smaller than 650 square feet", so the local two-space rule conflicts with state law for a two-bedroom detached unit under 650 sq ft. The city had not amended this rule as of October 21, 2026.

The code requires a minor conditional use permit for every ADU. Minor conditional uses are decided administratively by the Community Development Department as Land Use Authority (no public hearing), and a denial can be appealed to the Planning Commission; a building permit and a certificate of final occupancy are also required before the ADU may be occupied. State law now limits this step: Utah Code 10-21-304(3)(a) says the city's detached-ADU regulation may not "require a conditional use permit for a detached accessory dwelling unit if the proposed detached accessory dwelling unit is located in a primarily residential zone" (effective October 1, 2026), and 10-21-303(1)(a) already makes an internal ADU a permitted use in residential areas. The city had not amended its code to match as of October 21, 2026.

Neither the principal dwelling nor the ADU may be used for nightly or weekly rental. The ADU may not be sold or subdivided separately from the principal dwelling, and its occupants may not exceed one family as defined in the code. State law lets a city bar rentals shorter than 30 consecutive days for internal ADUs (10-21-303(3)(i)) and shorter than 90 consecutive days for detached ADUs (10-21-304(4)(b)(iv)), so Syracuse's nightly and weekly ban sits within those limits.