ADU rules in Pennington County

In unincorporated Pennington County a detached accessory dwelling is allowed only by Conditional Use Permit in the agriculture and residential zoning districts (AG, RCH, RR, LDR, SR-1, SR-2), decided by the Planning Commission after a public hearing. One accessory dwelling per lot; the lot must be at least 6,500 square feet, and on lots under one acre the unit cannot sit in the front yard. The county defines an accessory dwelling as a detached structure smaller than the single-family primary house, on a permanent foundation, and not a recreational vehicle. Each district's own lot size and septic minimums (for example 20,000 square feet for an on-site wastewater system) still apply.

No attached or internal ADU use exists (PCZO 324 is detached-only and the residential districts allow one dwelling per lot); a second unit attached to or inside a house is lawful only as a two-unit dwelling by right in SR-2. The ordinance calls that a multiple-family dwelling (two to four units), and in SR-2 it needs a lot of at least 7,500 square feet for up to two units and must meet §303 (a separate water heater and laundry hookups per unit, 300 square feet of private recreation and leisure area per unit on sites under 20,000 square feet, a screened refuse enclosure on a concrete pad) plus two parking spaces per unit under §310. Outside SR-2, §303(C)(1) allows a multiple-family dwelling only as a Conditional Use with a Planning Commission hearing under §510. Lots on septic still need the §204(M) minimums (20,000 square feet, or 43,560 with a private well).

An accessory dwelling may not exceed 700 square feet, two stories or two bedrooms, and its footprint must be smaller than the principal dwelling. Occupancy is capped at four persons or one family. Accessory structures in the residential districts are also subject to the district height limits in the §204 table (35 feet for all structures in the RR, LDR and SR-1 district text). A separate Efficiency Dwelling (tiny home) category under §330 caps units at 400 square feet.

The property must be owner-occupied as determined by the county Department of Equalization (that is, carrying the owner-occupied property-tax classification), unless the main dwelling is occupied as a long-term rental of 28 consecutive days or more. So an owner who lives off-site can still have an ADU if the main house is let long-term, but neither unit can stand empty while the other is short-term rented. The requirement is ongoing and is checked through the Planning Commission's periodic CUP reviews. South Dakota has no state owner-occupancy preemption.

Section 324 sets the minimum at one off-street parking space for the accessory dwelling. The general parking table in §310 requires two spaces per dwelling unit for single- and two-family dwellings, so the principal house keeps its own two; the ADU-specific section is the more specific rule for the second unit. The Planning Commission can attach additional conditions to the permit.

Every accessory dwelling needs a Conditional Use Permit under PCZO §510: a published notice at least 10 days ahead, registered or certified mail to owners within 500 feet, a posted sign, and a public hearing at which a favorable majority of the Planning Commission must approve. Appeals of the Planning Commission's decision go under SDCL 11-2-61.1. Approved ADU permits are reviewed afterward for compliance (§324(C)), and the 2026 Planning Commission agendas carry a steady run of ADU CUP and CUP-review items. A building permit under the county Building Code and Construction Ordinance No. 735 is also required. A two-unit dwelling in SR-2 is a use by right, so it needs only the building permit and staff review against §303; elsewhere a two-unit dwelling is itself a §510 conditional use.

An accessory dwelling may be rented for terms of at least 28 consecutive days, or as a Vacation Home Rental (VHR) under §319. A VHR in an ADU requires the approved §324 Conditional Use Permit, a county VHR License (required since June 26, 2024), and an owner-occupied property or a main dwelling held as a long-term rental; only one rental ADU is allowed per lot and the main dwelling cannot itself be a VHR. VHRs also need a local contact within 50 miles and are barred from floodways. Home occupations are prohibited in an accessory dwelling. A VHR rented more than 14 days a year also needs the state Department of Health lodging license (SDCL 34-18).