Colorado consistently ranks among the highest states for indoor radon concentrations. El Paso, Weld, Larimer, and Boulder counties all show elevated readings. If you are buying a home on the Front Range, a radon test is not optional — it is part of a responsible purchase.
What Radon Is
Radon is a radioactive gas that forms from the natural decay of uranium in soil and rock. It is colorless, odorless, and moves easily through foundation cracks, sump pits, and floor drains into living spaces. Outdoors, it disperses quickly. Inside a home, it accumulates.
The EPA sets 4 picocuries per liter (pCi/L) as the action level — the concentration at which mitigation is recommended. The national average indoor reading is about 1.3 pCi/L. Many homes we test in Colorado exceed 4. Some exceed 10.
Radon is the second leading cause of lung cancer in the United States, behind only smoking. That is not a small risk.
Why Colorado Is High
The geology under the Front Range is uranium-rich. The Rocky Mountain region formed from granite and other uranium-bearing rock. As that rock weathers, it releases radium, which decays into radon. Homes built on this soil — which is most of the Front Range — draw radon upward through any opening in the foundation.
The altitude and climate compound the problem. Colorado homes are well-sealed against cold, which reduces natural ventilation and allows radon to concentrate.
When to Test
Test during the inspection contingency period, before closing. A short-term test takes 48 hours and integrates into the standard inspection timeline without delay. If the reading exceeds 4 pCi/L, mitigation is the appropriate response — not panic.
Mitigation is a straightforward mechanical fix. A licensed contractor installs a sub-slab depressurization system: a pipe through the foundation connected to a small fan that draws radon from beneath the slab and exhausts it outside. The cost typically runs $800 to $1,500. Post-mitigation readings usually drop well below 2 pCi/L.
What Sellers Should Know
If your home has not been tested, test it before you list. A reading above the action level is not a transaction killer — a disclosed, mitigated system is a selling point. An undisclosed radon problem discovered by a buyer's inspector costs you leverage and time.
The Bottom Line
If you are buying a home in Colorado, add a radon test to your inspection. If you already own a home and have not tested in the past five years, test it. The test is inexpensive. The information it provides is not.