ADU rules in Yankton

Yankton's zoning chapter has no accessory dwelling use, and it expressly bars living in a backyard building: Sec. 27-4(i) says no building in the rear of any principal building on an interior lot may be used for residence purposes. Accessory buildings in the R-1 through R-4 districts are limited to garages, sheds, pools and like uses incidental to the principal building, and a lot is defined as occupied by one main building with accessory buildings. A two-family dwelling must be a single building occupied by two families, so a second detached house is not available through the duplex route either.

There is no accessory dwelling unit as such, but a second unit in the same building is allowed by right as a two-family dwelling in the R-3 two-family and R-4 multiple-family districts (and in B-1 and B-3, which carry R-4 or R-2 standards). R-3 requires 8,000 sq ft of lot area for a two-family dwelling (6,000 for single-family) and R-4 requires 6,000 sq ft. The R-1 and R-2 single-family districts, which cover most single-family neighborhoods, allow only one-family detached dwellings, so converting a basement or adding an attached unit there takes a rezoning. In B-2 a one- or two-family dwelling is a conditional use.

Because Yankton regulates the second unit only as part of a two-family dwelling, there is no square-footage or percent-of-house cap on either unit. The building as a whole must meet the district's bulk rules: in R-3 no more than 35 percent of the lot may be covered by buildings, height is capped at 2.5 stories and 35 feet, and yards are 25 ft front, 5 ft side and 25 ft rear. R-4 keeps 35 percent coverage but allows three stories and 55 feet after Ord. No. 1107 (5-26-2026). Minimum lot area for a two-family dwelling is 8,000 sq ft in R-3 and 6,000 sq ft in R-4.

Nothing in Chapter 27 requires the owner to live in either unit of a two-family dwelling, at application or afterward; a quoted search of the whole code for 'owner-occupied' returned no hits. South Dakota has no ADU owner-occupancy statute, so the question is purely local.

Single- and two-family dwellings need two off-street spaces per dwelling unit, so adding the second unit of a duplex adds two spaces, each at least 10 by 20 ft, paved with asphalt or concrete, and not in the required front yard. Ord. No. 1108 (5-26-2026) added a one-space-per-unit rate for two-family and multifamily dwellings designed and operated as rental housing exclusively for persons 55 or older. The B-3 central business district needs no off-street parking.

Where a two-family dwelling is a listed permitted principal use (R-3, R-4, B-1, B-3), the second unit is approved administratively: a building permit from the administrative officer with a scaled site plan and a parking plan, plus a use permit for a change of use of an existing house. No hearing is involved. Elsewhere the route is discretionary: a conditional use (plan commission hearing, then a city commission resolution) in B-2, or a rezoning in R-1 and R-2.

Either unit of a two-family dwelling may be rented long term; the code has no rental registration or licensing scheme. Chapter 27 defines a 'tourist home' (a dwelling offering overnight accommodations to transient guests) but lists it as a use in no district, so whether a whole unit may be rented nightly is a staff interpretation question, not a settled permission. Any stay under 28 days owes the extra 1 percent municipal lodging tax of Sec. 22-1/2-25, and a whole-home rental for more than fourteen days a year needs a state vacation home establishment license (SDCL 34-18-1).