Building an underground bunker in Montana.

Registration and permits

Montana requires construction contractors with employees to register with the Department of Labor and Industry under section 39-9-102 of the Montana Code. Outside jurisdictions the state certifies to enforce codes, Montana does not issue residential building permits, although homes must still meet the code and electrical and plumbing permits still apply. The Montana land guide covers that in more detail, along with exempt wells.

Frost and snow

Helena requires footings at least 42 inches deep; West Yellowstone requires 48. Montana State University publishes a ground snow load finder, the state sets a 30-pound minimum roof snow load, and mountain towns go far higher: West Yellowstone designs for 140 pounds per square foot of ground snow.

Deep frost changes how a bunker is built. Entries, vents and water lines are the weak points, so we bury them below frost or insulate them, and we keep the stair or hatch protected from drifting snow so it opens in February.

Earthquakes

The Montana Bureau of Mines and Geology describes the Intermountain Seismic Belt, up to 100 kilometers wide, running from Flathead Lake to Yellowstone, and the Centennial Tectonic Belt branching west into central Idaho with at least eight active faults. The state averages seven to ten small earthquakes a day. The magnitude 7.3 Hebgen Lake earthquake of August 17, 1959 killed 28 people and triggered the Madison Canyon landslide. Sites in the southwest of the state are engineered for it.

Radon

The Montana Department of Environmental Quality reports that about half of Montana homes tested are at or above 4.0 picocuries per liter, the federal action level, and that most counties fall in the EPA's highest radon zone. Montana's codes require a vapor retarder but not a mitigation system. In an underground shelter we go further: active sub-slab mitigation, a sealed shell and positive-pressure filtered air, confirmed by test.

Wildfire and septic

A 2023 report found Montana had no statewide wildland-urban interface code, and that local governments could not adopt stricter building codes. Wildfire design is therefore up to the owner and builder, and we treat it as standard: defensible space, ignition-resistant materials above grade, and filtered air below grade that can be sealed against smoke. Septic systems follow the state's DEQ-4 standards.

How we build in Montana

A Montana compound is planned around winter. The bunker sits below frost with its entries protected, the roof carries earth cover and a heavy snow load, power is sized for the shortest days, and fuel for a full season is stored on site. We also plan distance from the Minuteman missile field around Great Falls, which is noted on our HOLM map.

Escape openings

The International Residential Code, which these states and most of their counties build from, has a Section R310 that requires an emergency escape and rescue opening in basements and in every sleeping room below grade. A bunker is designed around that from the start: a second way out, sized and protected so it can be opened from inside after a storm, a fire or a collapse at the main entry. Some states amend R310, Utah among them, so we confirm the local version for each site.

Questions

This page is general information, current to October 2026. It is not engineering or legal advice. Codes, snow loads and frost depths are set locally and change; we confirm every requirement for a specific Montana parcel with the responsible jurisdiction before design.