Building an underground bunker in Idaho.

Registration and permits

Idaho requires contractors to register with the Division of Occupational and Professional Licenses under the Idaho Contractor Registration Act. Registration is not a competency license, so the qualifications of the engineer and builder deserve the questions in our 12 questions to ask any bunker builder.

Idaho adopts building codes by statute, but local enforcement is optional, and some rural counties do not inspect at all. We engineer and document every Idaho bunker to code either way. The Idaho land guide covers the domestic well exemption and the 2026 groundwater curtailments.

Rock and excavation

On the eastern Snake River Plain, the U.S. Geological Survey describes young basalt 1,000 to 2,000 feet thick across large areas, laid down in flows that average about 25 feet and have dense interiors. Depth to groundwater ranges from under 50 feet near Mud Lake to as much as 1,235 feet southwest of Craters of the Moon.

Basalt is a good roof once you are in it and an expensive hole to make. Where rock is shallow, we compare excavation against building at grade and berming earth over the structure, and we price rock work only after test pits or borings, never from a map.

Earthquakes

Central Idaho is seismically active. The magnitude 6.5 Stanley earthquake on March 31, 2020 was the second largest recorded in the state and was followed by more than 4,300 aftershocks. The largest, the magnitude 6.9 Borah Peak earthquake, struck in 1983. A bunker in the central mountains is engineered for those loads, with flexible utility entries and anchored storage.

Frost depth and snow loads

Frost depth is local: Coeur d'Alene requires a 24-inch minimum, Idaho Falls 30 inches and Teton County 32. Ground snow loads come from University of Idaho studies published in 1986 and 2015. Coeur d'Alene designs for 60 pounds per square foot of ground snow, Idaho Falls calculates its load from elevation, and Teton County requires an 85-pound roof minimum below 6,600 feet. We engineer the bunker roof for earth cover and snow together.

Radon

The Idaho Department of Health and Welfare states that two out of five Idaho homes have elevated radon levels. In a sealed underground space, that is a design requirement, not an option: sub-slab mitigation, a sealed shell, filtered air at positive pressure and a test before anyone sleeps below grade.

Septic

Idaho septic systems follow IDAPA 58.01.03 and are permitted by the state's seven public health districts. Where rock is shallow, the drain field is often the harder permit, so we confirm it before the bunker is placed and plan an ejector pump for any fixtures below the septic line.

How we build in Idaho

An Idaho compound starts with water and rock: a parcel where the domestic well exemption applies and the basin is not under curtailment, and test pits that show how deep we can go before we hit basalt. North Idaho brings more snow and timber; the southeast brings rock and wind. We design the bunker for whichever ground the family chooses.

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 Idaho parcel with the responsible jurisdiction before design.