What Causes Radon in Basements?

What is radon and why does it accumulate in homes? Radon is a naturally occurring radioactive gas that comes from the decay of uranium that is contained in the rock and soil beneath the basement (under the foundation) of every home. Since a home's basement is in constant contact with the ground, it is the primary entry point for radon gas.

Radon gas can seep into basements through multiple entryways, often going unnoticed until levels become hazardous. The most common pathways include cracks in concrete floors and walls, gaps around pipes and wiring, poorly sealed sump pump pits and even uncovered crawl spaces. Since radon is a dense gas, it accumulates in low-lying areas, making radon in basement spaces a widespread concern.

Conditions inside your basement can contribute to the radon level as well. When the pressure inside your basement varies greatly from the pressure outside it can create what is called “stack effect.” This process draws air more forcefully between the high and low-pressure areas and can pull more air from the rock and soil beneath your home impacting your radon levels.

Certain structural features in a home can also increase the risk of high radon level infiltration. Expansion joints, wall-floor intersections and porous foundation materials all create opportunities for radon to enter. Homes with aging foundations or extensive underground utility connections may also experience a radon problem due to unsealed access points.

Because these pathways allow radon to move freely into indoor air, monitoring radon concentration is essential. Homeowners should periodically check for foundation cracks, maintain proper sealing in vulnerable areas and use radon testing kits to track fluctuations over time. Identifying and addressing radon exposure risks early can help minimize health concerns.

See Related Article: Is Radon Only In Basements?

Radon gas is present in every home at varying levels, and it is nearly impossible to have a radon level of 0. However, there are ways to lower your radon levels.

There are simple ways to lower your radon levels, such as:

• Installing, replacing or sealing a sump well cover can reduce your levels as you will be closing up an exposed area of the earth with direct access into your basement.
• When the weather is nice, open windows and doors, to allow radon gas to dissipate with the fresh air.
• To reduce the stack effect, consider maintaining consistent indoor temperatures and sealing entry points rather than relying solely on temperature adjustments (especially when there are extreme outdoor temperatures).

Be advised that these tips can lower your radon level, but typically, small fixes like these will only lower your radon level slightly. If you have drastically high radon levels a radon mitigation system is the only way to reduce a dangerous level.

Many homeowners also keep appliances in the basement. When you know what causes radon in basements, you can be more cautious. The exhaust fans, water heaters, furnaces, fireplaces and dryers that you have in your basement reduce the air pressure indoors. This increases the stack effect, especially in very tight homes.

You may also need to consider reverse chimney flow if your house is overly depressurized. This can actually cause combustion spillage from the appliances you have in your basement if you are not careful.

Make sure that you have a radon detection kit in the most lived-in areas of your home. Detection is the first step in finding a solution when it comes to radon. Now that you know what causes radon in basements, it is time to protect yourself and your family.

Long-term exposure to radon gas poses serious health risks, with lung cancer being the most significant concern. As radon decays, it releases radioactive particles that can be inhaled into the lungs, damaging tissue over time. The EPA identifies radon as the second leading cause of lung cancer, responsible for thousands of deaths each year.

Both smokers and non-smokers are at risk, but smokers face an even greater danger when exposed to high radon levels. The combination of smoking and radon exposure dramatically increases the likelihood of developing lung cancer compared to either risk factor alone. That said, even non-smokers can suffer from respiratory complications when living in a home with elevated radon concentration. Radon is the leading cause of lung cancer in non-smokers.

Since radon has no odor, taste or visible presence, homeowners must take a proactive approach to detection and radon mitigation. Addressing radon concerns early can significantly reduce exposure and protect long-term health.

If a radon test detects levels of 4.0 pCi/L or higher, immediate action is necessary to lower exposure. The first step is improving ventilation and sealing common entry points to help reduce radon buildup. However – for consistently high readings – a radon mitigation system is the most effective solution.

Sub-slab depressurization is the most widely used mitigation technique, involving a vent pipe and fan system that redirects radon gas from beneath the foundation to the outside air. Other solutions – such as crawl space encapsulation and increased airflow through HVAC adjustments – can also help reduce radon concentration in homes.

Working with a qualified and certified radon mitigation specialist is recommended to assess the situation accurately and install the proper system. Professionals have the tools and expertise needed to create a long-term solution that effectively lowers radon levels and maintains indoor air quality.