Radon Basements: Why Denver's "Green" Homes Can Kill

By Franklin Everett Shaw

May 20, 2026

Is your “green” Denver basement secretly poisoning you? It’s a scary thought, but the energy-efficient features designed to save you money could be trapping a silent killer: radon.

Radon, a colorless, odorless, radioactive gas, is a naturally occurring byproduct of uranium decay in soil and rock. While it’s present everywhere, Denver’s unique geology, combined with modern, tightly sealed construction, creates a perfect storm for radon accumulation, especially in basements.

Think your energy-efficient basement is safe? Think again. The very features that make it “green” – improved insulation, airtight windows, and sealed foundations – prevent natural ventilation, allowing radon to build up to dangerous levels. This is particularly true in newer Denver homes built to stricter energy efficiency standards.

Here’s the harsh truth: many Denver homeowners are unknowingly living with elevated radon levels, putting themselves and their families at increased risk of lung cancer. The EPA estimates that radon is responsible for approximately 21,000 lung cancer deaths each year in the United States.

So, how do you know if your Denver basement is affected? You test.

DIY radon testing is surprisingly straightforward and affordable. You can purchase a short-term radon test kit at most hardware stores in the Denver metro area, including Home Depot, Lowe’s, and even smaller local shops like McGuckin Hardware in Boulder. These kits typically cost between $25 and $50.

Here’s a step-by-step guide to DIY radon testing in your Denver basement:

Choose the Right Test: Opt for a short-term test kit (2-7 days) for a quick assessment. Long-term kits (90 days or more) provide a more accurate annual average but require a longer waiting period. For initial screening, a short-term test is sufficient.
Prepare the Basement: Close all windows and exterior doors in the basement for 12 hours before starting the test. This helps to simulate typical living conditions and ensures an accurate reading. Don’t run fans or ventilation systems that draw air from outside.
Placement is Key: Place the test kit in the lowest livable area of your basement, ideally in a frequently used room. Avoid placing it near drafts, windows, exterior walls, or areas with high humidity. A central location, at least 20 inches above the floor, is ideal.
Follow Instructions Precisely: Each test kit comes with specific instructions. Read them carefully and follow them to the letter. Incorrect placement or handling can invalidate the results.
Send the Sample Promptly: After the testing period, seal the kit according to the instructions and mail it to the designated laboratory immediately. Radon levels can fluctuate, so timely analysis is crucial.
Interpret the Results: The lab will send you a report with the radon level in picocuries per liter (pCi/L). The EPA recommends mitigation if the radon level is 4 pCi/L or higher. Even levels between 2 and 4 pCi/L warrant consideration of mitigation.

But what if your test comes back high? Don’t panic. Radon mitigation is a common and effective process.

For mitigation, especially in Denver’s unique climate and with its specific building codes, professional installation is highly recommended. Denver’s clay soil can affect the performance of some mitigation systems, and a professional will know how to address these challenges.

Here’s what a typical radon mitigation system installation in Denver entails:

Assessment: A certified radon mitigation specialist will assess your home to determine the best mitigation strategy. This includes evaluating the foundation type, soil conditions, and ventilation systems.
Sub-Slab Depressurization: The most common method involves creating a suction point beneath the concrete slab of your basement. A pipe is inserted through the slab, and a fan draws radon gas from beneath the foundation.
Venting: The radon gas is then vented safely above the roofline, away from windows and air intakes.
Sealing: Cracks and openings in the foundation walls and slab are sealed to prevent radon from entering the home through other pathways.
Testing: After installation, the system is tested to ensure it’s effectively reducing radon levels below the EPA action level.

Common mistakes Denver homeowners make when dealing with radon:

Ignoring the Issue: The biggest mistake is simply not testing. Many people assume that because they live in a newer home or haven’t experienced any health problems, they’re not at risk.
Improper DIY Testing: Failing to follow the instructions carefully or placing the test kit in an inappropriate location can lead to inaccurate results.
Choosing the Cheapest Mitigation Option: While cost is a factor, selecting a less experienced or unqualified contractor can result in an ineffective or poorly installed system.
Assuming One Test is Enough: Radon levels can fluctuate over time. It’s recommended to retest your home every two years, even after mitigation.

Denver-specific challenges:

Clay Soil: Denver’s expansive clay soil can shift and crack foundations, creating pathways for radon entry. Mitigation systems need to be designed to account for this.
Altitude: Denver’s high altitude can affect the performance of radon mitigation fans. A professional will select a fan that is appropriately sized for the altitude.
Building Codes: Denver’s building codes require radon mitigation systems in new construction. However, older homes may not have these systems in place.

Financial assistance is available for low-income Denver homeowners who need radon mitigation. The Colorado Department of Public Health and Environment (CDPHE) offers a Radon Mitigation Assistance Program that provides grants to eligible homeowners. Contact CDPHE or your local county health department for more information.

Common misconceptions about radon in Denver:

“My neighbor doesn’t have radon, so I don’t either.” Radon levels can vary significantly from house to house, even on the same street.
“Radon is only a problem in older homes.” While older homes may have more cracks and openings, newer, tightly sealed homes can also trap radon.
“Opening windows will solve the problem.” While ventilation can help, it’s not a reliable long-term solution. A properly installed mitigation system is the most effective way to reduce radon levels.

Don’t let a silent threat compromise your health and the value of your Denver home. Take action today by testing your basement for radon. It’s a simple, affordable step that can protect your family and give you peace of mind. Remember, knowledge is power, and in this case, it could save your life.