HVAC Code Requirements in Montana

State with significant severe hail frequency per NOAA SPC storm reports. Insurance restoration contractors should document pre-existing hail damage and recommend impact-resistant materials.

Ground snow loads range from 25 psf on the eastern plains to 40+ psf in central Montana. Statewide base zone — see Mountain Snow Load overlay for western mountain counties with loads of 40-80+ psf. Spring snowmelt and wind-driven snow drifting are significant design considerations across the state.

Western Montana lies along the Intermountain Seismic Belt, one of the most seismically active regions in the interior United States. The 1959 Hebgen Lake earthquake (M7.3) near West Yellowstone was one of the most powerful earthquakes in US history. Helena experienced damaging earthquakes in 1935. Seismic Design Categories range from B (eastern Montana) to D (Yellowstone area, portions of western Montana). Affected counties include: Flathead, Lake, Lincoln, Mineral, Missoula, Ravalli, Sanders, Gallatin, Park, Madison, Beaverhead, Silver Bow, Deer Lodge, Powell, Granite, Lewis and Clark, Jefferson, and Broadwater.

Montana mountain areas have some of the highest ground snow loads in the continental United States. Ground snow loads range from 30 psf on the eastern plains to well over 150 psf in mountain areas such as Big Sky, Whitefish, Red Lodge, and mountain passes. Many locations exceed the IRC maximum prescriptive snow load tables and require site-specific engineering. Counties with extreme snow loads include: Flathead, Glacier, Lincoln, Mineral, Sanders, Lake, Missoula (mountain areas), Gallatin (Big Sky), Park, Carbon (Red Lodge), and Madison. Snow drifting against structures, unbalanced roof loads, and sliding snow are significant hazards.

Areas designated as Zone A, AE, or AO on FEMA Flood Insurance Rate Maps. Montana has significant riverine flood risk along the Missouri River, Yellowstone River, Clark Fork River, Flathead River, Milk River, and their tributaries. Spring snowmelt flooding is the primary flood hazard. Ice jam flooding also occurs on major rivers in winter/spring. Local jurisdictions participate in National Flood Insurance Program (NFIP).

Ice barrier underlayment is REQUIRED statewide on all roof eaves per IRC R905.1.2. Mean January temperature is well below 25°F across the entire state. Montana experiences extreme cold (design temps -20°F to -40°F) and heavy snow accumulation, creating persistent ice dam conditions especially in mountain communities.

Western Montana has extensive Wildland-Urban Interface (WUI) areas where residential development meets or intermixes with wildland vegetation. Major wildfire events have occurred in 2000, 2003, 2007, 2012, 2017, and 2021. High-risk counties include: Flathead, Lincoln, Mineral, Sanders, Missoula, Ravalli, Lake, Powell, Granite, Lewis and Clark, Gallatin, and Park. The Bitterroot fires of 2000 and the Lolo Creek Complex (2013) demonstrated the vulnerability of Montana WUI communities.