ADU rules in Teton County

Teton County calls ADUs accessory residential units (ARUs); the definition expressly includes a guesthouse and caretaker's quarters, and one ARU is permitted accessory to a detached single-family unit. The countywide Use Schedule allows ARUs in every character zone (NR-1, WHB, R-1, R-2, R-3) and most legacy zones, and since the 1/23/2023 amendments no use permit is required when the primary use is residential (a building permit still is). ARUs are not allowed in the Suburban (S-TC) and Mobile Home Park (MHP-TC) legacy zones and need a Conditional Use Permit in the Park (P-TC) zone. The catch is occupancy, not construction: ARU occupants must be Teton County workforce, family members, or nonpaying guests.

Attached and internal units qualify: the ARU definition includes an employee apartment and a mother-in-law suite, and Sec. 6.1.4.B.1.a.i classifies single-family units attached to accessory residential units as still being detached single-family units, so attaching the ARU does not change the primary use. The same occupancy restrictions and the 1,000 sf cap apply regardless of whether the ARU is attached or detached. In the Workforce Home Business (WHB) zone a second ARU is allowed on 3+ acre sites only if at least one ARU is attached to another structure and one is deed-restricted workforce.

Every zone that allows ARUs caps an ARU accessory to a residential use at 1,000 sf of gross floor area including basement (e.g. Secs. 2.2.1.E.1, 3.2.2.E.6, 3.2.3.E.3, 3.2.4.E), and its floor area also counts inside the primary dwelling's maximum floor area and scale of development (Sec. 6.1.11.B.3.d). ARUs accessory to a nonresidential use are generally capped at 850 sf and exempt from floor area calculations; in R-1, larger nonresidential-accessory ARUs are allowed at one per 35 acres. On 35+ acre R-1, R-2, R-TC, and WHB sites, the Floor Area Option (a conservation easement over 90 percent of the site) allows 2 additional ARUs per 35 acres of gross site area, each up to 5,000 sf gross, and an option ARU over 3,000 sf of habitable floor area triggers workforce housing mitigation. Historic structures are exempt from the maximum scale of use for an ARU (Sec. 6.1.11.B.3.g).

No LDR provision requires the property owner to live in either unit. Instead the LDRs restrict who may occupy the ARU: persons employed within Teton County under the Jackson/Teton County Housing Rules and Regulations (through a restriction mechanism acceptable to and enforceable by the Housing Authority), members of the same family occupying the primary dwelling, or intermittent nonpaying guests of the family occupying the main house. The family and guest pathways presume a family occupies the primary dwelling, but the workforce-rental pathway carries no owner-occupancy condition. The Housing Department administers tenant qualification with annual requalification for rented ARUs.

The countywide required parking table sets a minimum of 1.25 off-street spaces per dwelling unit for an accessory residential unit, on top of the 2 spaces per unit required for the primary detached single-family dwelling. The zone use tables repeat the same 1.25 per unit figure, so there is no zone-level deviation. Only vehicles used for daily travel may be stored outside an ARU; other vehicles and gear must be kept in an enclosed structure (Sec. 6.1.11.B.3.f).

Since the 1/23/2023 amendments (AMD2022-0004), an ARU whose primary use is residential requires no use permit at all: the Use Schedule marks ARUs with an asterisk, defined as use allowed without a permit if primary use is residential. A building permit (Sec. 8.3.3) and other physical development approvals, including a Natural Resources Assessment where applicable (Sec. 8.2.2), are still required. An ARU accessory to a nonresidential use takes a Basic Use Permit, an administrative Planning Director decision within 45 days of sufficiency with no hearing (Sec. 8.4.1); only the P-TC Park zone requires a Conditional Use Permit. Teton County enforces the 2024 IRC (permits filed on or after 2/1/2025), so Wyoming's Fast Track Permits Act (W.S. 16-13-102, effective 7/1/2026) adds a 30-day decision shot clock, with deemed approval on lapse, to completed residential building permit applications filed on or after July 1, 2026.

An ARU rental period must be at least 90 days, and occupancy is restricted to persons employed within Teton County per the Housing Rules and Regulations, family members of the household in the main house, or intermittent nonpaying guests; open-market rental to non-workforce tenants is not allowed. Under the December 2024 Housing Rules and Regulations, a qualifying household needs at least one member averaging 30 hours per week for a local business and 75 percent of household income earned locally, with annual requalification; ARUs developed after June 4, 2018 under the Housing Department's programs carry a recorded Special Restriction for Workforce Rental Housing. Countywide, no residential unit may be rented for under 31 days outside a short list of pre-1994 resort developments (The Aspens, Teton Village I and II, Spring Creek Ranch, Grand Targhee Resort and similar), and the county enforces violations found on Airbnb or VRBO with fines up to 750 dollars per day. The ARU may not be sold separately from the primary use (Sec. 6.1.11.A.4).