What Is Radon and Does Basement Flooding Increase It?
Last updated October 26, 2026
The short answer
What Is Radon
Radon is an invisible, odorless gas that forms when uranium in the ground decays. It seeps up through soil and can enter your home through gaps around pipes, crawl spaces, or cracks in the foundation. Once inside, it can build up, especially in lower levels like basements.
Long-term exposure to high radon levels is a health concern because it can damage lung tissue. The only way to know if your home has elevated radon is to test. Testing is simple and inexpensive, and you can do it yourself or hire a professional. If levels are high, mitigation systems can reduce them.
Does Flooding Affect Radon
Flooding itself does not create radon or increase its concentration in the air. Radon comes from the ground, not from water. However, a flood can shift soil, widen cracks, or damage your foundation, which may create new pathways for radon to enter your home.
Also, after a flood, your basement may be sealed or insulated during cleanup, which can trap radon that enters through those new cracks. So while flooding does not directly raise radon levels, it can change how easily radon gets in. Testing after a flood is a sensible step.
- Radon comes from uranium in soil, not from floodwater.
- Flooding can crack foundations or enlarge existing gaps.
- Wet soil can shift and create new entry points.
- Sealing a basement after a flood may trap radon.
- Testing is the only way to know your radon level.
When to Test After a Flood
If your basement has flooded, wait until the area is dry and any cleanup is complete. Then conduct a radon test. Short-term tests take a few days, while long-term tests last several months. Follow the instructions on the test kit carefully for accurate results.
If the test shows high levels, you can hire a radon mitigation professional to install a system. That system typically uses a fan and piping to pull radon from beneath the foundation and vent it outside. This work usually reduces radon levels significantly, but the exact outcome depends on your home's specific conditions.
Health Risks and Safety
Radon is the second leading cause of lung cancer after smoking, according to health agencies. The risk depends on the level and how long you are exposed. If you spend time in a basement with high radon, the risk increases. Testing is the only way to assess your exposure.
If you are concerned about your health, see a doctor. They can discuss your exposure history and any symptoms. Do not attempt to diagnose yourself. A medical professional can provide guidance based on your situation.
Cleanup and Prevention
After a flood, dry your basement thoroughly and fix any structural cracks. Sealing cracks can help reduce radon entry, but sealing alone is not always enough. A professional radon test will tell you if further action is needed.
For water damage cleanup, local water damage pros can help remove standing water and dry the area. They can also inspect for hidden moisture that might weaken your foundation. If you live in a flood-prone area, consider scheduling a water damage inspection after a flood to catch issues early.
- Dry the basement completely after flooding.
- Seal visible cracks in the foundation.
- Test for radon after the area is dry.
- Fix drainage issues to prevent future floods.
- Use a dehumidifier to keep humidity low.
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Call Now (305) 614-9705Frequently asked questions
Can radon come from floodwater?
No, radon comes from the soil and rock beneath your home, not from water. Floodwater can carry sediment, but it does not contain radon. However, flooding can create cracks or pathways that allow soil gas, including radon, to enter your home more easily.
How long does a radon test take?
Short-term radon tests typically last 2 to 7 days, while long-term tests last 90 days or more. Follow the test kit instructions for accurate results. After a flood, wait until the basement is dry and cleaned before testing to avoid false readings from moisture.
What should I do if my radon level is high?
If your test shows high radon, contact a radon mitigation professional. They can install a system that vents soil gas away from your home. Retest after installation to confirm the level has dropped. Also, continue to test periodically, especially after major flooding or foundation work.