Buying a Home in Colorado? What to Know About Radon

Colorado sits squarely in EPA Zone 1 for radon risk, and the Front Range corridor from Fort Collins through Denver to Colorado Springs has some of the highest indoor radon levels in the country. If you're buying a home here, radon should be on your due diligence list right next to the inspection and appraisal.

Why Radon Matters More in Colorado

The geology beneath much of Colorado is rich in uranium-bearing granite and shale. As uranium decays naturally in the soil, it produces radon gas that seeps upward through foundation cracks, sump pits, and construction joints. Homes built on the Front Range, in mountain communities like Evergreen and Conifer, and across the Western Slope regularly test above the EPA's 4.0 pCi/L action level.

The Colorado Department of Public Health and Environment recommends that every home in the state be tested for radon, regardless of age, construction type, or neighborhood. Newer homes with radon-resistant features still need testing — passive systems don't always keep levels below the action threshold without an active fan.

When to Test During the Buying Process

Most buyers in Colorado include radon testing as part of the inspection contingency. The standard approach is a 48-hour continuous radon monitor (CRM) placed in the lowest livable area of the home. A few things to keep in mind:

• Testing should happen with closed-house conditions — windows and exterior doors stay shut for 12 hours before and during the test.
• Short-term tests give a snapshot. If you plan to finish a basement later, consider that future living spaces may need their own test.
• Results above 4.0 pCi/L warrant mitigation. Results between 2.0 and 4.0 pCi/L are worth monitoring, especially in Colorado's climate where homes stay sealed for months during winter.

Negotiating Radon Mitigation in a Colorado Home Purchase

High radon results don't have to kill a deal. In most Front Range transactions, radon mitigation is a standard negotiation point. Common approaches include:

• Seller installs before closing. The seller hires a certified contractor to install an active soil depressurization (ASD) system and provides a post-mitigation test showing levels below 4.0 pCi/L.
• Seller credits the buyer. The buyer receives a credit at closing (typically $1,000–$1,500) to handle mitigation after move-in.
• Split the cost. Both parties share the expense, which works well when results are moderately elevated.

Colorado real estate agents are generally familiar with radon negotiations since they come up so frequently. Your agent should be able to guide you through typical local norms for your specific market — Boulder transactions may look different from Pueblo or Grand Junction.

What Mitigation Looks Like in Colorado Homes

The most common system is sub-slab depressurization, where a contractor drills through the basement slab, installs PVC piping, and uses a fan to draw radon gas from beneath the foundation and vent it above the roofline. In Colorado, most installations take a single day.

Costs typically run $800 to $2,000 depending on foundation complexity, number of suction points needed, and whether the home has a crawl space in addition to a slab. You can estimate costs for your situation using the radon mitigation cost calculator.

Post-installation, a follow-up test should confirm levels dropped below 4.0 pCi/L. Most properly installed systems in Colorado bring levels well below 2.0 pCi/L.

Finding Certified Contractors in Colorado

Colorado has 112 radon professionals across 50 cities in our directory — the highest density of any state. Major cities like Denver, Colorado Springs, Boulder, and Fort Collins all have multiple certified contractors available.

When comparing contractors, look for NRPP or NRSB certification, ask for references from recent installations in your area, and get at least two written quotes with itemized scopes. Browse all Colorado radon contractors to compare options near your property.

Colorado-Specific Considerations

A few things are unique to buying in Colorado's radon landscape:

• Altitude and ventilation. Colorado's dry climate means homes are often tightly sealed, which can concentrate radon. Homes at higher elevations don't necessarily have higher radon — it depends on the soil, not the altitude.
• New construction. Colorado building codes in many jurisdictions require radon-resistant new construction (RRNC) features, but these are passive systems. An active fan may still be needed if post-construction testing shows elevated levels.
• Seasonal variation. Winter readings in Colorado tend to be higher than summer readings because homes are sealed tighter. A winter test result is generally considered a conservative (higher) estimate.

Bottom Line for Colorado Buyers

Radon testing in Colorado is not optional — it's expected. The good news is that mitigation works reliably, costs are reasonable, and the state has a deep bench of certified professionals. Get your test done during the inspection period, negotiate mitigation if levels are elevated, and move into your new home with confidence. Use the radon assessment tool to get a personalized recommendation based on your situation, or find radon testing near you.