Radon: Frequently Asked Questions

 Radon poses a significant long‑term health risk, and this becomes especially important during the home buying and selling process. Colorado has some of the highest radon levels in the United States, with about half of all homes testing above the EPA’s recommended action level of 4.0 pCi/L . Because of this, radon testing and mitigation often become part of real‑estate negotiations, and many mortgage programs strongly encourage or require radon testing before closing.

National health authorities — including the Environmental Protection Agency (EPA), the U.S. Surgeon General, and the American Society of Home Inspectors (ASHI) — all recommend radon testing during real‑estate transactions to ensure buyers understand the home’s radon levels before finalizing the sale. Colorado’s Department of Public Health & Environment also advises that every home in the state be tested, regardless of age or construction type, due to statewide elevated radon levels.

 The EPA recommends testing your home every two years, or sooner if you’ve made major renovations, changed your HVAC system, or recently installed a mitigation system. Homes can shift, settle, or change airflow patterns over time, which may alter radon levels. 

 The EPA established the 4.0 pCi/L radon action level in 1986 as a practical threshold based on health risk, available measurement technology, and the feasibility of reducing radon levels in most homes. Radon levels can vary on a day-to-day and seasonal basis. The action level is based on a long-term 1-year test cycle. Radon is considered a long-term health risk. 

Colorado follows this same action level, and statewide data shows that many homes exceed it, with the average indoor radon level in Colorado around 6.8 pCi/L — far above the national average of ~1.3 pCi/L.

Radon is measured in picocuries per liter (pCi/L), a unit named after Marie Curie, the pioneering scientist who discovered radioactivity and became the first woman to win a Nobel Prize, as well as the only person to win Nobel Prizes in two different scientific fields (Physics in 1903 and Chemistry in 1911). This historical context helps explain why the unit carries her name.

While 4.0 pCi/L is the official action level, the EPA also recommends considering mitigation for levels between 2.0 and 4.0 pCi/L, because no level of radon exposure is completely risk‑free. The World Health Organization (WHO) sets an even lower recommended action level of 2.7 pCi/L 

 Colorado’s geology results in high radon potential in all 64 counties, and radon is recognized as the second leading cause of lung cancer in the U.S., and the #1 cause among non‑smokers. Because of this:

• Radon testing is commonly included in inspection contingencies
• Elevated results often require mitigation before closing
• Mitigation can be negotiated as a seller responsibility or buyer credit
• Post‑mitigation verification is typically required to confirm safe levels

Addressing radon early in the transaction helps avoid delays and ensures a smooth closing process.

 DIY test kits can be accurate if used correctly, but professional testing provides more reliable results because certified testers follow strict protocols and use calibrated equipment. The EPA and state agencies recommend using NRPP‑approved devices or hiring a licensed radon measurement professional for the most dependable results. 

 Yes. Radon can affect any home, regardless of age, foundation type, or construction style. Even brand‑new homes built to modern standards can have elevated radon levels. Radon enters through soil contact, so basements, crawlspaces, and slab‑on‑grade homes are all susceptible. 

 A properly functioning mitigation system should have:

• A clearly marked manometer or monitoring device showing system vacuum
• A continuously running fan
• Post‑mitigation test results confirming radon levels are below the EPA action level

The EPA recommends retesting your home every two years, after any major structural changes, and for Colorado specifically two seasonal changes - to ensure the system continues to perform effectively all year-round.

 Mitigation costs vary depending on the home’s design, but most systems fall within a predictable range. The EPA and state radon programs emphasize that mitigation is a high‑value investment because it reduces a known carcinogen, protects long‑term health, and increases buyer confidence during real‑estate transactions. Many buyers view a mitigation system as an asset, not a drawback.