ADU rules in Lewiston

A detached backyard unit is allowed outright, with no hearing. Sec. 37-131.2, as rewritten by Ordinance No. 4972 (passed 7-27-2026), permits one accessory apartment “within, detached from, or attached to a single-family dwelling” on any residential lot that is “zoned for single-family residential use” and “has only one (1) lawful single-family dwelling located on such lot”; the old requirement that the lot be at least five thousand square feet was struck. Sec. 37-3 folds the arrangement into the by-right use by defining “Dwelling, single-family” as “a detached building containing one (1) dwelling unit or one (1) dwelling unit with an accessory apartment,” and the “Dwelling, multifamily” definition expressly excludes “one (1) single-family dwelling with an accessory apartment.” Single-family dwellings are permitted outright in every zone that allows housing: F-2, R-1, R-2, R-2A, R-3, R-4, Normal Hill North and Normal Hill South. The limit is one accessory apartment per lot, and the lot may not already hold a second dwelling.

Attached wings, over-garage units and internal conversions run on the same by-right track as detached ones. Sec. 37-131.2 now opens “Only one (1) accessory apartment, within, detached from, or attached to a single-family dwelling”; Ordinance No. 4972 inserted “within,” which settles the old question of whether a pure basement or attic conversion fell inside the phrase. The same ordinance repealed Secs. 37-41.11 and 37-41A.11 outright, the Normal Hill North and Normal Hill South sections that had allowed “only one (1) accessory apartment, detached from a single-family dwelling” and so read as barring attached units in those two historic-era neighborhoods. One uniform citywide standard now applies. Municode has not yet codified the repeal, so both Normal Hill sections still appear on the platform.

Ordinance No. 4972, passed 7-27-2026, rewrote Sec. 37-131.2(1) to read “An accessory apartment shall not exceed one thousand (1,000) square feet or seventy-five (75) percent of the habitable floor area of the associated single-family dwelling, whichever is greater,” striking both the old six hundred square foot and thirty percent figures and the flat nine hundred square foot ceiling that used to override them. The two-bedroom cap in subsection (2) gave way to a requirement that the unit “adhere to the maximum lot coverage allowance of the applicable zoning district,” which is 40 percent in R-1, R-2 and R-2A, 50 percent in R-3 and R-4, and 60 percent in Normal Hill North and South. The ten-foot rear setback and the 18-foot single-story and 28-foot two-story height caps were struck as well, replaced by one rule that an accessory apartment “shall not exceed the building height of the associated single-family dwelling.” The old numbers sat below the floor Idaho Code 67-6541(2)(d) and (f) require covered cities to adopt by February 1, 2027 (no size limit under 1,000 square feet or 75 percent of the primary dwelling, and no height limit below the existing house), which is what the rewrite was for.

Nobody has to live on the property. What Sec. 37-131.2 requires is common ownership, not occupancy: “An accessory apartment shall be owned by the same person who owns the single-family dwelling to which such accessory apartment is attached to or detached from.” That blocks selling the unit away from the house but says nothing about who occupies either dwelling, and no other provision of Chapter 37 conditions an accessory apartment on owner residency. Ordinance No. 4972 kept the clause and simply renumbered it from (8) to (6). Idaho Code 67-6541(2)(e) points the same way: by February 1, 2027 each covered city (Lewiston, at roughly 34,000 people, is far above the statute's 10,000 threshold) must “Prohibit an owner-occupancy requirement for the primary dwelling or for the accessory dwelling unit.” The only owner-occupancy rule in Lewiston's residential toolkit attaches to a different use: Sec. 37-3 defines a “bed and breakfast” as “an owner-occupied residence.”

Ordinance No. 4972, passed 7-27-2026, struck the old flat rule (“At least one (1) off-street parking space shall be provided for an accessory apartment”) and substituted “An accessory apartment shall provide a minimum of one (1) off-street parking space per bedroom, up to a maximum of two (2) off-street parking spaces unless one (1) or more of the following conditions exist,” listing (a) the principal dwelling unit does not have off-street parking, (b) the street serving the property is not paved or is not designed or constructed for on-street parking, as determined by the public works director or designee, and (c) the principal dwelling unit is within one-fourth mile of a public transit fixed route shown on the city's transit route map, an employment area, or commercial services, as determined by the community development director or designee. The subsection closes: “If any of the conditions in subsections (3)(a) through (3)(c) are met, no off-street parking shall be required for the accessory apartment.” Read against the statute the test runs backwards. Idaho Code 67-6541(2)(b) directs cities to “Prohibit requiring any off-street parking or guest parking for any accessory dwelling unit unless the principal dwelling unit does not have off-street parking or the street is not paved and designed or constructed for on-street parking or unless the principal dwelling unit is within one-fourth (1/4) mile of transit, an employment area, or commercial services,” so the state allows a parking requirement in the same three situations where Lewiston waives one, and bars a requirement in the ordinary case where Lewiston imposes one. In practice most Lewiston lots near a transit route or a commercial strip end up with no ADU parking requirement at all.

Administrative from end to end: there is no accessory apartment application, no conditional use permit and no public hearing. Because Sec. 37-3 defines a single-family dwelling to include “one (1) dwelling unit with an accessory apartment,” the unit rides the by-right single-family listing in each zone's “Uses permitted outright” section (for example Sec. 37-27(10) in R-2), and the Article IX conditional use machinery never engages. Sec. 37-191 supplies the only zoning sign-off: no structure may be used “until a zoning certificate, which may be a part of the building permit, shall have been issued by the community development department.” From there it is the ordinary residential permit set (building, electrical, plumbing, mechanical) through Building Services. Idaho Code 67-6541(3) has reinforced this since July 1, 2026: conforming ADU projects “shall be approved administratively and as a matter of right, without the need for discretionary approval.” The exception is design review, not use review: in the Lewiston West End Historic District and in the Normal Hill Heritage Overlay, the Historic Preservation Commission must issue a certificate of appropriateness before a building permit can be issued.

Lewiston has no short-term-rental regime to comply with: full-text searches of the Code of Ordinances for “short-term rental,” “vacation rental” and “Airbnb” still return zero hits, and Chapter 21 (Business Licenses) has no lodging or rental license article. Nothing restricts long-term renting either; Chapter 37 sets no minimum lease term, no tenant cap and no registration for an accessory apartment. The one ownership rule is Sec. 37-131.2's requirement that the same person own both the house and the accessory apartment, which prevents selling or condominiumizing the unit separately but does not touch renting it. Idaho Code 67-6539, rewritten by 2026 ch. 22 effective July 1, 2026, would foreclose local STR rules anyway: no city ordinance may prohibit any type of short-term rental, owner-occupancy conditions, day limits, numeric caps, extra parking, inspections and conditional use permits in residential zones are all listed as forbidden “different restrictions or obligations,” and subsection (5) provides that no city “shall require a license, fee, permit, certification, or registration to operate a short-term rental.” Generally applicable noise, parking, nuisance and traffic rules still apply under subsection (6). Renting rooms with breakfast is a separate zoning use: a “bed and breakfast” under Sec. 37-13.1(1) must be owner-occupied, is limited to five guestrooms and needs one off-street space per guestroom.