Colorado has some of the highest radon levels in the western United States, with an estimated average indoor radon level around 6.2 pCi/L — well above the EPA action level of 4.0 pCi/L. The Colorado Department of Public Health and Environment estimates that approximately 50% of Colorado homes have elevated radon. Colorado’s geology — including uranium-rich geological formations in the Front Range, granitic bedrock, and shale — creates high radon potential across much of the state, including the heavily populated Denver metro corridor.
EPA Radon Zone Designation
Colorado is predominantly EPA Radon Zone 1. Most Front Range and mountain Colorado counties are Zone 1. The highest-risk areas include counties along the Front Range corridor (El Paso, Jefferson, Arapahoe, Adams, Boulder, Larimer counties) and the western slope counties overlying uranium-bearing geology. Eastern plains counties are generally Zone 2 to Zone 3.
Radon Contractor Licensing in Colorado
Colorado requires radon contractors to hold current NRPP or NRSB certification to perform radon measurement and mitigation work. The Colorado Department of Public Health and Environment’s radon program maintains a list of certified radon professionals. Colorado does not have a separate state radon contractor licensing statute independent of national certification — NRPP or NRSB certification is the operative requirement. Verify contractor certification at nrpp.info or nrsb.org before hiring.
Radon Disclosure Requirements in Colorado
Colorado does not have a radon-specific disclosure statute for residential real estate transactions. However, Colorado’s general real estate disclosure law requires sellers to disclose known material adverse facts — and known elevated radon test results almost certainly qualify as a material fact under this standard. Real estate contracts in Colorado routinely include radon contingencies, and radon testing during the inspection period is standard practice in the Front Range metro area. The Colorado Real Estate Commission’s disclosure form does not include a specific radon question, but agents and sellers have a common law duty to disclose known adverse conditions.
Radon-Resistant New Construction (RRNC) in Colorado
Colorado has enacted RRNC requirements for new residential construction in high-radon areas. Some Colorado municipalities — particularly in El Paso County (Colorado Springs) and the Denver metro — require RRNC features for new construction. The IRC Appendix F provisions have been adopted in various Colorado jurisdictions. The CDPHE strongly recommends RRNC for all new construction in Colorado’s Zone 1 areas. Buyers of new Colorado construction should confirm with the builder and local building department whether RRNC is required and what specific provisions apply.
Highest-Radon Counties and Areas in Colorado
Colorado’s highest-radon areas include Front Range counties: El Paso (Colorado Springs area), Jefferson (Denver west suburbs), Arapahoe, Adams, Boulder, and Larimer counties. Mountain counties including Eagle, Summit, Park, and Teller also show elevated radon. Western slope counties overlying uranium-bearing geology in the Grand Junction area (Mesa County) have historically high readings. The CDPHE maintains county-level radon data on their website.
Testing Resources for Colorado Residents
The Colorado Department of Public Health and Environment administers the state radon program and provides resources for homeowners including lists of certified contractors, low-cost or free test kit programs (availability varies by year and funding), and technical guidance on radon mitigation. Contact the state radon program directly for the most current contractor list, any available test kit distribution programs, and jurisdiction-specific requirements that may have changed since this page was last updated.
Frequently Asked Questions
Is Colorado a high-radon state?
Yes. Colorado has one of the highest average indoor radon levels in the western U.S., estimated at 6.2 pCi/L statewide. Approximately 50% of Colorado homes test above the EPA action level. Radon is a significant public health concern across Colorado’s Front Range and mountain communities.
Does Colorado require radon disclosure in real estate?
Colorado has no radon-specific disclosure statute, but sellers have a common law duty to disclose known material adverse facts — including known elevated radon levels. Radon contingencies and testing are standard in Colorado real estate transactions.
What counties in Colorado have the highest radon?
El Paso, Jefferson, Arapahoe, Adams, Boulder, and Larimer counties along the Front Range have high average radon levels. Mountain counties including Eagle, Summit, Park, and Teller also show elevated readings. Western slope counties near Grand Junction have historically high concentrations.
