ADU rules in Ketchum

A detached backyard ADU is allowed as an accessory use in every residential and mixed-use district in Ketchum: LR, LR-1, LR-2, GR-L, GR-H, the three Short Term Occupancy districts (STO-.4, STO-1, STO-H), the three Tourist districts (T, T-3000, T-4000), both Community Core districts (CC-1, CC-2) and Agriculture and Forestry (AF). The code's definition covers 'an attached or detached dwelling', and Table 16-7 marks the use 'A' rather than 'C', so no conditional use permit is involved. The lot must already have a one-family dwelling on it: 16.03.040.B.4.a limits ADUs to an accessory use of a one-family dwelling, and an ADU cannot be added to a multi-family building. Only the three Light Industrial districts (LI-1, LI-2, LI-3) and the Recreation Use district (RU) leave the cell blank, which Table 16-7's key reads as prohibited. These rules are new: Ordinance 1260 replaced the old Title 17 zoning code with Title 16, the Ketchum Land Development Code, effective January 1, 2026.

Attached and internal ADUs are treated identically to detached ones. The definition at 16.08.020 reads 'An attached or detached dwelling that is accessory in nature to a principal residential unit', and the single standards section at 16.03.040.B.4 draws no distinction between a basement conversion, an addition and a separate building. The city's own guidance puts it plainly: an ADU may be new construction or converted from existing space such as a garage or basement. The one structural limit is that ADUs go with one-family dwellings and 'are not to be constructed as an addition to a multiple-family unit'.

16.03.040.B.4.b sets a floor of 300 square feet and a ceiling of 1,200 square feet of net livable space, which 16.08.020 defines as floor area inside the perimeter walls of the dwelling unit, so garages and mechanical rooms do not count against the cap. Bulk is controlled separately: the ADU plus the principal dwelling must fit the underlying district's maximum building coverage, but a new ADU earns an increase of up to five percent in that coverage, except in the Community Core district. Two general accessory-use rules can bind before the 1,200 sq ft cap does on a small lot: total building coverage of all accessory buildings cannot exceed the principal building's coverage (the Administrator may grant an exception), and a detached ADU takes its setbacks from its own height rather than the house's. There is no ADU-specific height limit, so the district maximum applies, for example 35 feet and 35 percent coverage in the LR district.

Nothing in the Ketchum Land Development Code requires the owner to live in either unit. 16.03.040.B.4 imposes exactly five ADU standards (accessory use, unit size, maximum building coverage, parking, storage) and none of them touches occupancy, and a sweep of all of Title 16 for owner-occupancy language turns up nothing. The only ownership limit is in the definition itself: an ADU 'cannot be sold separately from the principal residence', so the two units stay on one deed. Note that this is a local choice rather than a state mandate. Idaho Code 67-6541(2)(e), the statewide ban on ADU owner-occupancy requirements enacted in 2026, applies only to cities over 10,000 population and therefore does not reach Ketchum.

16.03.040.B.4.d is one sentence: accessory dwelling units do not require off-street parking. The off-street parking schedule at Table 16-13 carries no ADU row, and the two spaces it requires per one-family dwelling attach to the house, not to the ADU. The city advertises this as an ADU incentive alongside waived fire, parks, police and street impact fees. What the ADU does need is storage: at least 50 square feet of designated storage outside ordinary closets.

An ADU is an accessory use ('A' in Table 16-7), not a conditional use, so there is no hearing and no discretionary land use approval. In most cases the only permit is a building permit, reviewed by Planning staff for zoning compliance; the city says initial comments come within 21 business days and later rounds within 10. Design review, Ketchum's discretionary design process, expressly exempts one-family dwellings, accessory structures and accessory dwelling units, but only when they are not in the Mountain Overlay district. On a hillside lot inside that overlay an ADU does need design review under 16.02.070.D.4, and a preapplication design review before the Planning and Zoning Commission is required for new development on lots totaling 11,000 square feet or more. Extra permits can also apply in a floodplain, in the Avalanche Overlay district or inside certain planned unit developments.

Ketchum places no limit on renting an ADU long term: there is no license, no lease-length floor and no owner-occupancy tie, only the rule that the ADU cannot be sold separately from the principal residence. Short-term rental is itself a permitted 'P' use in every residential and mixed-use district under Table 16-7. The city's short-term rental permit chapter, Ketchum Municipal Code 5.09, is still printed in the codified book and still says no one may rent short term 'without first obtaining and maintaining a short-term rental (STR) permit', with a two-night minimum and one STR per parcel in residential zones. That regime became unenforceable on 1 July 2026, when Idaho Code 67-6539(5) as rewritten by H0583 barred any city from requiring 'a license, fee, permit, certification, or registration to operate a short-term rental' and separately banned inspections, day limits, numeric caps and residential-zone conditional use permits. Ketchum is unwinding its ordinance: Ordinance 1277 repeals and replaces chapter 5.09 with voluntary standards, passed first reading on 11 June 2026 with combined second and third readings set for 25 June 2026, and the city has taken its STR application offline and told owners they face no penalties for not applying. What survives is the short list Idaho still allows: smoke alarms, a fire extinguisher and carbon monoxide detector per floor, escape ladders above the ground floor, building-code occupancy limits and an informational handout.