ADU rules in Columbia Falls

Chapter 18.411, as rewritten by Ordinance 843 (effective July 15, 2026) and now printed on the city's code site, makes accessory dwelling units 'a permitted use on any residential lot' without restricting their form. The chapter contemplates freestanding units: ADUs are 'subject to the maximum lot coverage of the applicable zone, height restrictions for the primary structures, and setbacks for the accessory dwellings'. Before July 15, 2026 the old Accessory Apartment chapter allowed a unit in a detached garage or stand-alone structure only through a conditional use permit in CR-1 through CR-4. Columbia Falls has completed its Montana Land Use Planning Act transition, so this local chapter, not the statewide ADU statute, is the operative rule.

Section 18.604.027 defines an accessory dwelling unit simply as 'A dwelling unit that is accessory to the primary dwelling', and § 18.411.010 makes ADUs a permitted use on any residential lot without distinguishing attached, internal, or detached forms. An ADU in an addition, attic, or basement is therefore allowed on the same terms as a detached one. Internal units were also lawful under the pre-2026 chapter, which allowed an accessory apartment within the primary residence 'such as attic or basement'.

Section 18.411.010 provides that an ADU 'is limited to 75% of the gross floor area of the single-family dwelling or 1,000 square feet, whichever is less', the same formula as Montana's statewide ADU statute. This replaced the former 800 sq ft cap on July 15, 2026. The ADU also counts toward the zone's maximum lot coverage (25% in CSAG-5, 30% in CR-1 through CR-3, rising to 45% in CRA-1), is held to the 35-foot height limit for primary structures in the residential districts, and follows the accessory-building setbacks of § 18.410.030 (no accessory structure in a front yard, and at least five feet from rear and side lot lines).

Neither Chapter 18.411 nor any other Title 18 provision requires the owner to live in the house or the ADU. The state Land Use Planning Act's ADU housing strategy speaks of a lot 'with a single-unit dwelling occupied as a primary residence' (MCA 76-25-302(1)(e)), but that menu wording describes which lots a city must open to ADUs, and Columbia Falls' adopted zoning text attaches no occupancy condition. The pre-2026 accessory apartment chapter imposed none either, so owner occupancy has never been required here.

Chapter 18.411 sets no parking standard for ADUs and the residential parking chapter (18.504) has no ADU line, so no added space is required for the ADU; Ordinance 843 removed the old one-space rule for accessory apartments. Section 18.502.010(F) adds that 'Where state law prohibits minimum parking requirements, this title shall be interpreted as imposing no minimum', and since October 1, 2026 MCA 76-25-303(1)(j), as amended by HB 492 (Laws of Montana 2025, ch. 682), bars a city under the Land Use Planning Act from imposing 'any minimum parking requirement for ... residential units under 1,200 square feet', which covers every ADU allowed here. For the house, § 18.504.010 still prints one space (one half space under 1,200 sq ft), but the same state bar and § 18.502.010(F) cap it at one space and remove it below 1,200 sq ft. An ADU run as a licensed vacation rental must provide 'a minimum of one off-street parking space' under § 18.445.020, a rule that may conflict with the state bar for units under 1,200 sq ft.

ADUs are 'a permitted use on any residential lot' (§ 18.411.010), and the 2026 rewrite deleted the conditional-use lists from every zoning district, so an ADU needs only a ministerial zoning check and a building permit, with no hearing. The staff-issued Special Provision Permit described in § 18.316.010 covers uses designated as special provisions, such as vacation rentals, and is not required to build an ADU. Until July 15, 2026 the printed code listed 'Accessory Apartment' as a conditional use in CR-1 through CR-4, a requirement that was already void from January 1, 2024 under the statewide ADU statute, which bound the city until its Land Use Planning Act transition.

Section 18.411.010 provides that ADUs 'shall be rented for a period of not less than one month unless the property owner has received a Special Provision Permit for Vacation Rentals pursuant to Chapter 18.445'. That administrative permit is available in the CSAG-5, CR-1 through CR-5, CRA-1, CB-1, CB-2, CB-4 and CB-5 districts; its standards include a named local contact, one off-street space per rented unit, a passing Fire Marshal inspection, a Montana Public Accommodation License for a Tourist Home through the Flathead City-County Health Department, no signage, and the permit number on every listing, and the city may terminate it after four months of permit, bed tax, or resort tax delinquency. Nothing authorizes selling an ADU separately; it remains an accessory use on the same lot.