ADU rules in Custer

Detached ADUs are a permitted accessory use in Custer's single Residential District (R), the only district whose use lists name ADUs. Chapter 17.34 (Ord. 897, 2023) defines a detached ADU as 'a stand-alone home on the same lot as a larger, primary structure' and allows one per property, which must already have a principal structure. A detached ADU uses the accessory-building setbacks (front and side yards as for the house, rear yard as little as 12 feet).

Attached and internal ADUs are allowed on the same terms in the R district: the definition covers a unit 'within or attached to' the single-family dwelling, and § 17.34.040(A) allows the one ADU 'within or attached to the principal structure, or ... in a detached structure'. An attached ADU needs its own independent entrance and exit beyond the building-code egress, and must meet the full dwelling setbacks (25 ft front and rear, 6 ft sides).

Custer sets no fixed square-foot cap and no minimum: an ADU 'shall not exceed the square footage of the primary dwelling' and may have no more than two bedrooms. Height is limited to 25 feet or the height of the house, whichever is less, repeated in the R district height rule. Lot coverage is governed only by the R district setbacks (7,500 sq ft minimum lot for a new house).

Chapter 17.34 has no residency requirement: it requires only that 'the primary dwelling and the accessory dwelling unit shall remain in common ownership', so both units may be rented long-term and the owner need not live on site. South Dakota has no ADU statute, so nothing at the state level adds or preempts such a rule. Owner presence matters only for hosted short-term rentals, which ADUs may not be anyway.

Each ADU 'shall be designated at least one off-street parking spot', in addition to the one off-street space the R district requires for the single-family dwelling. The citywide parking table (§ 17.04.090, Ord. 917) likewise requires one space per dwelling unit for residential structures, with spaces at least 9 by 18 feet; the Central Business District exemption does not reach the R district, where ADUs are allowed.

ADUs meeting Chapter 17.34 are listed among the R district's permitted accessory uses, not its conditional uses, and 'construction of accessory dwelling units requires a building permit as outlined by Chapter 15.04', so approval is a staff building permit against the § 17.34.040 checklist. A unit that cannot meet a standard needs a variance under Chapter 17.48 (in 2026 practice a Planning Commission recommendation followed by a Board of Adjustment vote, per the September minutes). Each ADU must also obtain its own address for emergency purposes and share the principal structure's city utility services.

Long-term rentals (more than 30 consecutive days), which the code defines to include ADUs, are a permitted principal use in the R district. ADUs 'shall not be used as short-term rentals or hosted short-term rentals', and § 17.12.080(F) (Ord. 922, 2024) repeats that ADUs may not be hosted short-term rentals; whole-home short-term rentals (under 30 days) are prohibited in the R district outright, and hosted ones (owner present, conditional use) are limited to the principal structure. The common-ownership rule bars selling the ADU separately. The state Department of Health vacation-home license (SDCL 34-18) is moot for an ADU because the local ban applies first.