Building an underground bunker in Colorado.

Licensing and codes

Colorado does not license general contractors at the state level; the state consumer protection office says so directly. Cities and counties license them instead, and Denver, for example, does not recognize licenses from other jurisdictions. Electricians and plumbers are licensed by the state, which also issues electrical and plumbing permits where no local program exists.

Counties may adopt a building code but are not required to. Our Colorado land guide covers water rights, which are tightly held and expensive.

Expansive soil

The Colorado Geological Survey reports that expansive clays, including bentonite, underlie many populated areas, mostly in the valleys and plains, and cause more property damage than any other natural hazard in the state. Swelling pressure can reach 30,000 pounds per square foot, with volume growing 10 percent or more when the clay gets wet.

A buried structure has that clay against every wall. We test for swell potential before siting, and design the drainage, backfill and structure to keep water away from the clay and the clay away from the walls.

Frost depth

Frost depth is set by county and rises with elevation. Grand County designs to 30 inches, Jefferson and Pitkin counties to 36, and Hinsdale County to 36 inches below 10,000 feet and 48 inches above it. Entries, vents and water lines are buried below frost or insulated.

Wildfire

The Marshall Fire, which started on December 30, 2021, destroyed 1,109 homes in Boulder County. In 2023 the legislature created the Wildfire Resiliency Code Board, and its code took effect on July 1, 2025; local governments with areas on the state wildfire risk map had to adopt it, or something stricter, by June 30, 2026. We design every Colorado compound to that code, and the bunker's filtered air can be sealed against smoke.

Hail, floods and earthquakes

The Front Range sits in Hail Alley, with three or four catastrophic hailstorms a year between mid-April and mid-August. Floods are the deadlier risk: the 1976 Big Thompson flood killed 143 people, the 2013 floods reached 14 counties, and burn scars raise the risk of debris flows. In the Raton Basin, injected wastewater has caused most earthquakes since 2001, including a magnitude 5.3 in 2011 that damaged 46 structures.

A bunker is never sited where floodwater can reach it. FEMA does not support placing shelters where floodwater could endanger the people inside.

Radon and septic

The Colorado Department of Public Health and Environment reports that about half of Colorado homes are above the federal action level of 4 picocuries per liter, and that every county is in the EPA's highest radon zone. Every bunker we build there gets active mitigation and a test before use. Septic systems follow the state's Regulation 43 and are permitted by the county.

How we build in Colorado

We look for Colorado land on the Western Slope and in the southern valleys, with senior water rights and room from the Front Range. The bunker is sited after soil testing, out of any flood path, and engineered for frost, swelling clay and the mountain snow on top of it.

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 Colorado parcel with the responsible jurisdiction before design.