ADU rules in Vermillion

Vermillion has no accessory dwelling unit use, and a backyard cottage is expressly barred: Sec. 155.071(C) says accessory buildings 'may not be used for dwelling purposes'. A lot 'may include 1 main building together with its accessory buildings' (Sec. 155.008, LOT), so a second detached house on a single-family lot is not possible in R-1 or R-2. The only exception is R-3, where 'More than one main building per lot may be constructed' for multiple-family development (Sec. 155.034(C) exception #5); that is a two-building multifamily project on an R-3 lot, not an accessory unit behind a house. Tiny homes were studied by the Planning and Zoning Commission in 2024 and 2025 (only as grouped 'small neighborhoods' in R-3 and R-4), but no ordinance has been adopted.

There is no attached or internal ADU use, but a second unit inside or attached to a house is lawful as a duplex. A 'multiple-family dwelling' (which the code says includes a DUPLEX) is 'a building, or portion thereof, containing 2 or more dwelling units' (Sec. 155.008), so a basement or addition apartment with its own kitchen turns the house into a multiple-family dwelling. That use is permitted by right in R-2 (Sec. 155.033(A)) and R-3 (Sec. 155.034(A)) on a lot of at least 7,500 sq ft and 50 ft frontage (75 ft at the building line in R-2). It is not allowed at all in R-1, which permits only single-family detached dwellings plus conditional single-family attached townhomes (Sec. 155.031), or in the R-T townhome district, so most R-1 owners would need a rezoning.

Because there is no ADU use, no ADU size cap exists. A two-unit building in R-2 is governed by the multiple-family row of the lot table: 7,500 sq ft minimum lot, 50 ft frontage, 75 ft building line, 25 ft front and rear yards, 8 ft side yards, 35 ft maximum height, a maximum of 16 bedrooms per lot and no more than 4 bedrooms per dwelling unit (Sec. 155.033(C)). In R-3 the same use needs 7,500 sq ft for up to 32 bedrooms per lot, with a 60 ft height limit (Sec. 155.034(C)). Accessory buildings themselves have no hard cap, but those over 750 sq ft 'should be approved only if there is a legitimate residential purpose' (Sec. 155.071(D)), and they cannot be lived in.

Nothing in Chapter 155 requires an owner to live in either unit of a duplex; the code's only owner-occupancy rule is for bed and breakfasts, which must be 'an incidental use with an owner-occupied principal dwelling structure' (Sec. 155.080(C)). South Dakota has no state ADU owner-occupancy rule. A rented unit does have to be registered under the Rental Housing Code, and an owner or manager must live within 100 miles (Sec. 94.05(B)), which is a management rule, not an occupancy requirement.

Table 2 of Sec. 155.072 requires 2 off-street parking spaces per dwelling unit for 'Multiple-family (maximum of 2 dwelling units)', the same rate as a single-family house, so converting a house to a duplex means adding 2 spaces. Two-unit buildings may park on a driveway in the front yard (Sec. 155.072(A)(1)(a)), the code lays out an ordered list of where new spaces may go (existing driveway first, then a widened driveway, alley access, rear yard), and one garage stall within 10 ft of the unit may count if it stays open for resident or tenant parking 'as a condition of their rental registry' (Sec. 155.072(B)(3)). All parking must be hard surfaced (Sec. 155.072(A)(5)).

Where a second unit is allowed (a multiple-family dwelling in R-2 or R-3), it is a permitted use, so the route is a building permit issued by the Building Official after the Zoning Administrator confirms zoning compliance (Sec. 155.099(A)); the city takes residential addition, remodel and new-construction permits online through GovWell. No conditional use hearing applies in those districts. In R-1 and R-T there is no permit route at all: Sec. 155.099(A)(3) bars a building permit for a noncompliant use, and the Board of Adjustment cannot grant a use variance (Sec. 155.100(B)(2)), so only a rezoning under Sec. 155.101 would allow a second unit.

A duplex unit may be rented long term, but every rental unit must be registered with and inspected by the Housing Inspector before occupancy and renewed by January 15 each year, with a per-unit fee set by resolution (Sec. 94.05(A), (C), (G), (I)); the owner or a manager must live within 100 miles (Sec. 94.05(B)). The family definition caps occupancy at 4 unrelated adults per dwelling unit (Sec. 155.008) and the rental code adds no more than 2 unrelated persons per bedroom (Sec. 94.01). Vermillion's code has no vacation home or short-term rental provision; the only lodging use in a house is a bed and breakfast, which must be owner-occupied, at least 1,800 sq ft and registered with the state Department of Health (Sec. 155.080). A whole unit rented nightly for more than 14 days a year would also need a state vacation home establishment license (SDCL 34-18-1(17)).