West Glacier

Flathead County (Kalispell county seat; northwest Montana; ~115,000 residents and one of the fastest-growing counties in Montana — ranked among the top 5% nationally for inbound migration 2020-2024; bounded south by Flathead Lake — the largest natural freshwater lake west of the Mississippi — bounded north by Glacier National Park and the Flathead National Forest, west by the Salish Mountains, east by the Swan Range and Great Bear Wilderness) DOES maintain a comprehensive countywide zoning regime. Unlike most rural Montana counties, Flathead operates an extensive system of zoning districts under MCA Title 76 Ch. 2 Part 1 (county zoning) covering most of the populated unincorporated valley floor and shoreline corridors. The Flathead County Zoning Regulations include explicit ADU provisions in most residential zoning districts and a separate 'guest house' standard in lower-density residential zones. Montana SB 528 (MCA § 76-2-345) preempts MUNICIPAL ADU restrictions; Kalispell (~28,000), Whitefish (~8,400), and Columbia Falls (~5,800) all clear the SB 323 5,000-resident duplex-preemption threshold and are squarely subject to SB 528 ADU preemption. The Flathead Valley is also Montana's most active short-term rental (STR) market — Whitefish and the Flathead Lake corridor are among the highest-priced STR markets in the Mountain West. STR pressure has driven aggressive local ordinance activity in Whitefish (STR moratorium / cap measures) and Flathead County (STR registration and use-permit requirements in resort zoning districts). SB 528 ADUs cannot be conditioned on owner-occupancy or restricted from rental, but the legal interaction between SB 528 ADU preemption and local STR regulation is unsettled — local STR rules can apply to the resulting unit's USE without conflicting with the ADU preemption.

State-floor overlay: Montana SB 528 (MCA § 76-2-345) establishes a state floor for ADU permissibility in incorporated cities; Kalispell, Whitefish, and Columbia Falls (all >5,000 pop) are squarely subject. Flathead County's countywide zoning regulations independently allow ADUs in most residential districts.

Flathead County's overlay footprint is among the most extensive in Montana, reflecting its mix of resort-lake / Glacier-NP-gateway / mountain-WUI / floodplain geographies. Five overlay categories are material: (1) Montana Lakeshore Protection (MCA Title 75 Ch. 7 Pt 2) covering Flathead Lake, Whitefish Lake, Tally Lake, Lake Five, Lake Mary Ronan and others — joint DNRC/county jurisdiction with mandatory permits for any structure within 20 vertical feet of high-water mark. (2) FEMA NFIP floodplain along the Flathead River (North/Middle/South Forks confluence), Whitefish River, Stillwater River, Swan River. (3) Wildland-Urban Interface — Glacier NP, Flathead National Forest, Whitefish Range, Swan Range, Salish Mountains all surround the populated valley; multiple devastating wildfire seasons 2017-2024 have prompted county WUI mapping and recommendations though no countywide WUI building-code overlay has been formally adopted. (4) Glacier NP gateway zoning protecting view corridors and adjacency to NPS land along US-2 and the West Glacier / Polebridge approach. (5) Multiple NRHP historic districts (Kalispell, Whitefish, Columbia Falls, Bigfork) administered by city historic-preservation programs.

• Montana Lakeshore Protection Act - Flathead Lake, Whitefish Lake, others — Lakeshore-zone ADUs are heavily regulated. Many lakefront parcels are non-conforming under current setbacks and any expansion can trigger a variance. Premium STR economics make compliance worthwhile but timeline is long (60-90 days for permit beyond standard building permit).
• FEMA NFIP Special Flood Hazard Areas - Flathead River, Whitefish River, Stillwater River, Swan River — A new ADU in a mapped SFHA must be elevated to or above the Base Flood Elevation; elevation cost can add $20,000-$50,000 in this market. Glacier NP downstream effects from spring snowmelt drive late-spring flooding peaks.
• Wildland-Urban Interface - Glacier NP gateway, Whitefish Range, Swan Range, Flathead National Forest — Voluntary Firewise USA participation is widespread. Insurance markets are tightening: some carriers have stopped writing new homeowner policies in the Whitefish / Bigfork forested zones. ADU economics need to factor in higher insurance cost (15-30% premium versus equivalent valley-floor parcel).
• Glacier National Park Gateway / Adjacent-Lands Zoning — The 2024 federal designation expansions for grizzly recovery and lynx critical habitat have not directly affected Flathead County zoning but are routinely cited by environmental groups in opposition to upzoning proposals.
• Kalispell, Whitefish, Columbia Falls, Bigfork NRHP Historic Districts — ADU work on a NRHP-listed contributing property triggers Section 106 review only if federal financing or permitting (FHA, USDA RD, HUD-184) is involved.

Flathead County operates a full-service Planning and Zoning Office that issues building permits and zoning permits for parcels in unincorporated territory throughout the county. Unlike the small rural Montana counties, Flathead has fully opted in to county building-code enforcement and has a robust permitting infrastructure built up over decades of growth. The Flathead County Building Department administers the state-adopted Montana Building Code (currently 2018 IBC/IRC with 2024 amendments) for unincorporated parcels. ADU intake follows a standard residential-permit track with separate zoning verification for compliance with the parcel's zoning district (R-1, R-2, R-3, R-4, R-5, AG, RS, etc., each with different ADU permissibility and size standards). The Flathead Lake shoreline zones (LR-1 Lakeshore Residential, LR-2, etc.) impose additional setback, lot-coverage, and shoreline-protection requirements administered jointly with the Montana Department of Natural Resources and Conservation (DNRC) under the Montana Lakeshore Protection Act (MCA Title 75 Ch. 7 Part 2). Kalispell, Whitefish, and Columbia Falls operate their own city building departments inside city limits.