ADU rules in Riverton

Riverton's zoning code has no accessory dwelling unit of any kind, and nothing authorizes a detached second home on a house lot. Title 17 is a permissive-list code: § 17.16.010(A) bars using land or buildings 'for any purpose or in any manner other than that permitted in the district,' and the R-1 list at § 17.28.010 runs to one-family dwellings, modular or manufactured homes, accessory buildings and uses, parks, utility lines and a licensed family child care home. An 'accessory building' is defined at § 17.08.010 as 'a detached subordinate building, the use of which is customarily incidental to that of the main building,' and § 17.20.030 repeats that an accessory use must be 'clearly incidental' and 'customary,' so a backyard cottage with its own kitchen and bath is not an accessory building under this code. Where a second unit is allowed at all (R-2, R-2A and R-4), the code allows it only as a 'multiple-family dwelling,' which § 17.08.010 defines as 'a building occupied by two or more families living independently of each other,' meaning both units share one building. A whole-code text sweep of all eighteen titles on 2026-08-04 found zero occurrences of accessory dwelling, accessory residential unit, secondary dwelling, guest house, guest quarters, caretaker unit, mother-in-law or carriage house.

There is no ADU category, but an attached or internal second unit is possible in some districts because Riverton permits small two-unit buildings. In R-2, § 17.32.010(A) permits 'Multiple-family dwellings containing not more than two living units,' and § 17.32.020(C) caps living units at 'two on any one lot or parcel'; R-2A picks up the same rules because § 17.36.010(C) says all R-2A uses must comply with Chapter 17.32; R-4 goes further and permits multiple-family dwellings 'with any number of living units per building or parcel' (§ 17.40.010(A)). So converting a basement or building an addition into a second self-contained unit is a permitted use in R-2, R-2A and R-4, and in the less restrictive commercial districts by way of § 17.16.100(A)(a). It is not available in R-1, the city's 'limited one-family' district, where a 'one-family dwelling' is defined as 'a building designed exclusively for, and occupied by, one family' (§ 17.08.010); in R-1 the only routes are a rezone by ordinance under § 17.04.050 or a board of adjustment variance under § 17.04.040(G)(3). Check the parcel's district on the city's zoning map before planning anything.

Because Riverton has no ADU category, it has no ADU square-footage or percent-of-primary-dwelling cap. What binds instead is a floor: § 17.32.030(C) requires 'The floor area of each living unit in a multiple-family dwelling must be a minimum of 425 square feet with not less than 425 square feet on any one level,' and § 17.40.030(B) sets 300 square feet per unit in R-4 buildings with more than two living units. The house itself must still be at least 850 sq ft on the first floor above ground (§ 17.32.030(B)). The real constraints on how big a second unit can be are the envelope rules: maximum building height 35 feet in R-1, R-2 and R-2A and 50 feet in R-4, with not more than 40% of the lot covered by the main and accessory buildings (50% in R-4), plus the § 17.16.070 setbacks of 20 ft front, 5 ft side and 5 ft rear on an interior lot.

Nothing in Title 17 conditions a dwelling unit on the owner living on the property. The permitted-use lists for R-1, R-2, R-2A and R-4 (§§ 17.28.010, 17.32.010, 17.36.010, 17.40.010) attach no residency test, and the lot-area, floor-area and height rules are all physical. The only owner-occupancy requirement anywhere in the zoning title is embedded in the definition of a lodging use: § 17.08.010 defines a 'bed and breakfast inn' as 'an owner-occupied dwelling unit or portion thereof, where short-term (not more than five consecutive nights) lodging rooms and meals are provided for compensation.' Wyoming has no statewide ADU statute that would either impose or preempt an owner-occupancy rule, so this is purely a local absence. Note that the city's own 2019 Comprehensive Master Plan recommends that if Riverton ever legalizes ADUs it should require the main dwelling to be owner-occupied, so an owner-occupancy rule could arrive with any future code amendment.

The numbers are not in the municipal code. RMC 15.36.010 says only that 'the city of Riverton parking guidelines have been established to offer guidance,' that they 'will be published on the city's website,' and that council may adjust them by resolution. The operative document is the City of Riverton Parking Regulations, adopted in 2018 under Ord. 18-008 and posted on the Community Development zoning page. Its Table 15.36.030-1 requires 2 spaces per dwelling unit for a detached single-family dwelling and 2 per dwelling unit for a duplex, so a house plus a second living unit needs four spaces; there is no reduced ADU line item and no transit or small-unit exemption. Section 15.36.020(a)(2) makes this bite on conversions: an 'addition' includes 'any alteration intended to enlarge or increase capacity by adding or creating dwelling units.' Section 15.36.020(b)(1) requires spaces for dwellings to sit on the same parcel as the main dwelling, in a garage or on a paved driveway or parking area, and bars new residential parking in the required front yard except the driveway and any parking on an unpaved front-yard surface.

Where a second living unit is allowed, it is a listed permitted use, not a discretionary one: § 17.32.010 and § 17.40.010 say 'The following uses shall be permitted,' and there is no conditional-use or special-exception track for dwellings in Title 17. Review is administrative under § 17.04.030: the building official enforces the title, grants building permits and certificates of occupancy, and issues the permit once the applicant files a statement of intended use and a plat showing the lot, the building location and dimensions. The discretionary bodies enter only if you need relief: the board of adjustment hears appeals and hardship variances (§ 17.04.040), and a rezone out of R-1 is an ordinance with a planning commission hearing, 140-foot mailed notice and three council readings (§ 17.04.050). Since July 1, 2026 the state Fast Track Permits Act also applies here, because Riverton zones under W.S. 15-1-601 and has adopted the 2024 International Residential Code at RMC 15.04.010 (Ord. 25-003, 3/18/2025): applications filed on or after that date get a written completeness notice within 10 business days, an approve-or-deny decision within 30 calendar days of a completed application, written denial reasons within 7 days, and deemed approval if the 30-day clock lapses (W.S. 16-13-101, 16-13-102). That act governs timing only; it does not create any right to build a unit the zoning code does not permit.

A lawfully created second living unit can be rented long term without any city permission: a text sweep of all eighteen code titles on 2026-08-04 found no short-term rental, vacation rental, transient occupancy, rental license, rental registration or lodging tax provision, and Title 5 (Business Licenses and Regulations) covers only alcohol, child care, pawnbrokers, door-to-door solicitation and temporary merchants. The definition of 'occupied' at § 17.08.010 expressly contemplates units 'rented or leased.' Short-term rental is genuinely unsettled here: § 17.32.010(F) permits 'Bed and breakfast inns, duly licensed' in R-2 and less restrictive districts, and § 17.08.010 defines that use as an owner-occupied dwelling unit or portion of one supplying lodging of not more than five consecutive nights plus meals, while 'hotels and motels' (10 or more guest rooms) are not permitted in residential districts. Whole-unit nightly rental of a second unit fits neither definition and is neither expressly authorized nor expressly banned, so ask Community Development before counting on it. Selling the second unit separately is a further step: § 16.04.040 defines a 'subdivision' to include any parcel used for condominiums, apartments, a triplex or any other multiple dwelling.