ADU rules in Columbia Falls

Ordinance 843 (final reading June 15, 2026, effective July 15, 2026) replaced the old Accessory Apartment chapter with Chapter 18.411, Accessory Dwelling Unit, making ADUs 'a permitted use on any residential lot' with no restriction on form; the chapter contemplates freestanding units by applying accessory-structure setbacks and the zone's lot coverage. MCA 76-2-345(1)(b) separately guarantees that the required by-right ADU 'may be attached, detached, or internal'. Before Ord. 843 the printed code allowed a detached accessory apartment (in a detached garage or stand-alone structure behind the front of the house) only through a conditional use permit in the CR-1 through CR-4 districts; that discretionary requirement had already been void under MCA 76-2-345(5) since January 1, 2024.

Attached and internal units (attic, basement, addition) are equally covered: new § 18.604.027 defines an accessory dwelling unit simply as 'a dwelling unit that is accessory to the primary dwelling', and § 18.411.010(D) makes ADUs a permitted use on any residential lot without distinguishing form. Internal units have been lawful under both regimes; the pre-2026 chapter expressly allowed an accessory apartment 'within the primary residence such as attic or basement'. MCA 76-2-345(1)(b) confirms attached and internal ADUs statewide.

New § 18.411.010(A) adopts the state formula verbatim: an ADU 'is limited to 75% of the gross floor area of the single-family dwelling or 1,000 square feet, whichever is less', matching MCA 76-2-345(1)(c) ('gross floor area' means interior habitable area). This replaced the former 800 sq ft cap (with a conditional use permit needed to exceed it) on July 15, 2026. ADUs are also subject to the zone's maximum lot coverage, the height limits for primary structures (35 feet in the residential districts, consistent with MCA 76-2-345(2)(g)), and the setbacks for accessory structures (generally 5 feet from rear and side lot lines under § 18.410.030).

Neither the rewritten Chapter 18.411 nor any other Title 18 provision requires the owner to live in either unit, and MCA 76-2-345(2)(c) forbids a Montana city from requiring 'that the single-family dwelling or the accessory dwelling unit be occupied by the owner'. The pre-2026 accessory apartment chapter imposed no owner-occupancy condition either, so this has never been a requirement in Columbia Falls.

Ordinance 843 removed the former rule that one off-street space be provided for the accessory apartment: the rewritten Chapter 18.411 imposes no parking standard and the residential parking chapter (18.504) has no ADU line (a single-family dwelling itself needs 1 space, or half a space if under 1,200 sq ft). MCA 76-2-345(2)(a) has barred municipal ADU parking mandates and fees in lieu since January 1, 2024, so the old printed requirement was void before its repeal. If the ADU is operated as a licensed vacation rental, the STR permit separately requires one off-street space per rented unit under § 18.445.020(D).

ADUs are 'a permitted use on any residential lot' (§ 18.411.010(D)), and the June 2026 rewrite eliminated conditional use permits from Title 18 altogether; the only administrative overlay, the staff-issued Special Provision Permit of § 18.316.010, does not apply to ADUs. Review is therefore ministerial zoning conformance plus a building permit (Columbia Falls contracts building inspection through the Whitefish building department). MCA 76-2-345 caps any ADU-specific application fee at a one-time $250 plus normal building fees, allows the city to require will-serve letters from municipal water and sewer, and defines 'by right' to exclude hearings, variances, and conditional or special permits. Until July 15, 2026 the printed code listed 'Accessory Apartment' as a conditional use in CR-1 through CR-4; that CUP requirement was void from January 1, 2024 under MCA 76-2-345(5).

Section 18.411.010(B) keeps the city's long-standing rule that an ADU 'shall be rented for a period of not less than one month' unless the owner holds a Special Provision Permit for Vacation Rentals under Chapter 18.445. That STR permit is administrative and available in CSAG-5, CR-1 through CR-5, CRA-1, and the CB business districts; its standards include a named local contact, one off-street space per rented unit, a fire department inspection, a Montana Public Accommodation License (Tourist Home) through the Flathead City-County Health Department, no on-site signage, and the permit number on every listing, with termination possible after four months of permit, bed tax, or resort tax delinquency. MCA 76-2-345(3) expressly preserves local short-term rental regulation, so this regime stands alongside the by-right ADU mandate. Nothing authorizes selling an ADU separately; it remains an accessory use on the same lot.