ADU rules in Rapid City

Detached ADUs are allowed as an accessory use (RCMC 17.50.210.A.8) in the LDR-1, MDR, HDR, LDR-2 and General Agricultural districts, but not in the Park Forest district, where an ADU may only be part of the single-family house. A detached ADU also needs a lot of at least 6,500 square feet (smaller lots may have an internal or attached ADU only) and may not sit in the front yard. One ADU per single-family lot.

An ADU within or attached to a single-family dwelling is allowed in the LDR-1, MDR, HDR, LDR-2, General Agricultural and Park Forest districts, with one ADU per owner-occupied single-family dwelling. ADUs exist only in conjunction with a single-family dwelling; the code does not provide for an ADU with a duplex or multifamily building.

Rapid City sets no numeric floor-area limit for an ADU. A detached ADU must be smaller than the house's footprint, not counting an attached garage, may not cover more than 10% of the lot, and total lot coverage must stay within the district maximum. Detached units over 500 square feet must have a residential appearance. District height rules cap accessory buildings at 15 feet in PF, LDR-1, MDR and LDR-2; deviations need a Zoning Board of Adjustment variance.

The owner must live full time on the property, in either the main dwelling or the ADU, as shown on the Pennington County tax assessment rolls. The requirement is ongoing: no ADU may be created, established, or occupied without it. South Dakota has no state ADU law preempting owner-occupancy rules.

A single-family dwelling with an ADU must provide at least 2 off-street spaces for the main dwelling and 1 for the ADU, a minimum of 3. Parking must meet city standards including the Infrastructure Design Criteria Manual. If the ADU is used as a vacation home, the parking table assigns 2.00 spaces per vacation home and converting a dwelling to a vacation home counts as initiating a use.

ADUs are a permitted accessory use registered administratively with the Department of Community Development: the owner files a registration form with a site plan and floor plans, pays the registration fee set by council resolution plus any building permit fees, and staff register or deny the unit. No public hearing applies; staff denials and director revocations are appealable to the City Council. An unregistered ADU is not an approved permitted use.

Nothing in the code bars renting an ADU long term. The 2019 ADU ordinance (Ord. 6363) barred vacation home use of ADUs; Ord. 6714 (case 26OA001, adopted 5-18-2026, effective 6-12-2026, codified) replaced that with subsection S, which lets an ADU be a vacation home that complies with 17.50.410. A vacation home needs an annual city registration, a South Dakota Department of Health lodging license for a vacation home establishment, at most 2 persons per bedroom plus 2, and must be a permitted use in the district (5 bedrooms or fewer in PF, LDR-1, MDR, HDR and LDR-2). The 17.50.219.C owner-occupancy rule still applies, so the owner must live in the house or the ADU.