By Prerna Kapoor, CLHMS | REAL Brokerage | March 29, 2026
When you’re buying a home in Colorado, there’s one invisible threat you absolutely need to understand: radon. It’s colorless, odorless, and tasteless, which means you can’t detect it without testing. Yet about 50% of Colorado homes sit above the EPA’s action level for radon, making this one of the most critical inspections you’ll do during your buying process.
I’ve helped countless buyers work through radon testing and mitigation in Colorado. Let me walk you through what you need to know.
What Is Radon and Why Should You Care?
Radon is a radioactive gas that comes from uranium in soil and rock. It seeps into homes through cracks in foundations, gaps around pipes, and other openings. Over time, radon exposure can cause serious health problems.
The numbers are sobering. Radon is the second leading cause of lung cancer after smoking, responsible for about 21,000 deaths per year in the United States. Even if you’re a non-smoker, radon exposure significantly increases your lung cancer risk.
Colorado specifically sits in the zone with some of the highest radon levels in the country. We rank 8th nationally for average radon levels, and counties like Douglas, Arapahoe, and El Paso County have particularly high concentrations.
Colorado’s Radon Levels: The Statistics You Need
Here’s what the data tells us: roughly 50% of Colorado homes test above the EPA’s action level of 4 picocuries per liter (pCi/L). That’s significant. For comparison, the national average is closer to 40%.
The EPA action level isn’t a “safe” threshold. It’s a level above which the EPA recommends taking action to reduce radon. Any level above 4 pCi/L warrants mitigation. Some experts argue that even lower levels warrant concern, but 4 pCi/L is the official guideline.
If you’re buying in Parker, Aurora, Lone Tree, Castle Pines, or Highlands Ranch, you’re in areas where radon testing should be non-negotiable. These Denver metro communities sit in zones prone to elevated radon levels.
Radon Testing: What to Expect
Professional radon testing is straightforward but requires patience. A certified professional will place testing equipment in your home’s lowest livable level (typically a basement or main floor) and let it sit for a minimum of 48 hours. The house must be closed during this period, meaning windows and doors stay shut and HVAC systems run normally.
This 48-hour closed-house condition is important. It gives you the most accurate picture of radon levels under normal living conditions. Some inspectors will test for longer periods (up to 10 days) for more data, but 48 hours meets EPA standards.
Professional testing typically costs between $100 and $300, depending on your home’s size and the testing company. This is money well spent for your health and peace of mind.
When Should You Test?
If you’re a buyer, radon testing should be part of your inspection contingency. Include it when you hire a home inspector. The earlier you test, the more time you have to negotiate with the seller if levels are high.
Colorado law requires sellers to disclose known radon test results. If a seller has tested their home, they must share those results with you. Ask your real estate agent to request any existing radon test reports during the inspection period.
If you’re a seller, many buyers will request radon testing as part of their due diligence. Being transparent about radon levels and any mitigation systems you’ve installed builds trust and often strengthens your negotiating position.
Understanding Your Test Results
Radon levels fluctuate naturally. Temperature, barometric pressure, and seasonal changes all affect how much radon enters your home. A single test gives you a snapshot, not a guarantee.
If your first test shows levels between 2-4 pCi/L, many professionals recommend a second test to confirm. If levels are above 4 pCi/L, mitigation is recommended. If they’re above 8 pCi/L, it’s urgent.
Your test results are specific to that moment in time and those testing conditions. Once you close on a home, you’ll have the option to test again for a longer-term average.
Radon Mitigation: What It Costs and How It Works
If testing reveals high radon levels, mitigation systems are highly effective. A good radon mitigation system can reduce radon concentrations by up to 99%. You don’t have to live with high radon levels in your Colorado home.
A typical radon mitigation system pulls radon from below your foundation and vents it safely above your roof. The process prevents radon from entering your living spaces. Many systems run quietly in a basement corner or crawlspace.
Cost varies based on your home’s construction and complexity. Expect to spend between $800 and $2,500 for a professionally installed system. Some homes cost less, others more. Your mitigation contractor can give you a specific quote after assessing your foundation type and construction.
Good news: some new construction homes in Colorado come with passive radon systems pre-installed. These systems work without electricity and can be activated if testing shows they’re needed. Ask your builder if your new construction home includes a passive system.
Negotiating Radon Issues During Closing
Let’s say you test a home and find elevated radon. Now what? You have several options when negotiating with the seller.
You can ask the seller to install a mitigation system before closing. This shifts the cost and responsibility to them and gives you verification that the work was done professionally.
Alternatively, you can ask for a credit toward your closing costs to handle mitigation yourself after closing. This gives you control over the contractor selection.
You can also request that the seller provide proof of a mitigation system they’ve already installed, along with testing results showing it’s working effectively.
In my experience, most sellers are willing to address radon if you frame it reasonably. It’s a health issue, not a cosmetic problem, and most people understand that.
After You Close: Long-Term Radon Management
Once you own your home, radon testing becomes a personal choice. The EPA recommends testing every 2 years, or whenever you make major structural changes that might affect radon levels.
If you’ve had a mitigation system installed, you should periodically check that it’s operating properly. Many systems include simple indicators showing they’re working. Your mitigation contractor can provide guidance on maintenance.
If you find radon levels drop significantly over time (which happens in some homes due to seasonal changes or natural fluctuations), you might retest to confirm before spending money on a system.
Colorado Radon: The Bottom Line
Radon is real in Colorado. It’s common, it’s serious, and it’s manageable. Don’t let fear stop you from buying a home you love. Instead, test with confidence, understand your results, and take action if needed.
As your real estate advisor, I’ve guided many buyers through radon testing and mitigation. It’s a normal part of Colorado home buying. The key is approaching it informed and proactive.
Your health matters. Your home matters. Both deserve attention before you close on your Colorado property.
Thinking about buying or selling a home in Colorado?
Your home journey should feel exciting, not overwhelming. As your trusted advisor, I am here to make sure it does.
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Prerna Kapoor is a REALTOR® and Certified Luxury Home Marketing Specialist (CLHMS) with REAL Brokerage, specializing in residential real estate across Parker, Aurora, Lone Tree, Castle Pines, Highlands Ranch, Cherry Creek, Greenwood Village, and Centennial. She is fluent in English, Hindi, and Japanese (native) and is recognized as an International Sterling Society Award winner (2023, 2024, 2025). Prerna holds the RENE (Real Estate Negotiation Expert), PSA (Pricing Strategy Advisor), and ABR (Accredited Buyer’s Representative) designations.
Data Sources: EPA Radon Information
