Radon Inspection and Testing Guide

Radon is a dangerous gas. Learn about the risks of exposure and how to test your home for it.

Written by Angela Bunt Updated 01/09/2024

You may be encouraged to conduct a radon test if you’re building or buying a home. All homeowners should take this important safety measure, as radon exposure can have deadly consequences. This guide explains the health risks of radon exposure, prevention measures, and how to inspect your home.

What Is Radon?

Radon (Rn) is an odorless, colorless, tasteless radioactive gas that naturally occurs in soil and water, particularly groundwater. Only a small percentage of radon originates from drinking water. According to the Environmental Protection Agency (EPA), radon exposure is the second leading cause of lung cancer after smoking. It significantly increases the risk of lung cancer in smokers especially.

The only way to know if there’s an actionable level of radon in your home is to perform a radon test. The test must be performed according to the test manufacturer’s instructions to get an accurate result.

Any home can have an actionable radon level, defined as a level of radon that’s hazardous to your physical health. The EPA recommends that all homeowners test their homes for radon, but some homes are more likely to have actionable radon levels than others.

Your location determines how likely your home is to have a high radon level. The EPA website provides a map of radon zones by state and county. Level 1 or 2 is considered high.

Neighborhoods within a county can have a higher or lower radon level than is indicated on the map. It’s also possible that soil under your home could have been obtained from an area with high levels of radon. This is why the EPA recommends testing all homes.

When To Test for Radon

Most home buyers perform a radon test when they purchase their home. Many home inspectors, especially those in high radon areas, provide radon tests as an added service.

Consider performing a radon test if you didn’t do so when you bought your home, particularly if you live in a Level 1 or 2 area. You can test your home for radon yourself or hire a professional.

You won’t need to perform additional radon tests if your home has a non-actionable radon level and you don’t make significant changes to your property. Perform another test after radon mitigation and every few years following if you have an actionable radon level. This ensures the radon reduction system is functioning properly.

Types of Radon Tests

There are two types of radon tests:

The container test is the most common do-it-yourself (DIY) radon test. You can buy one at a hardware store or online. Many are short-term radon tests that run for a few days to a week, but some are long-term tests that last several months.

Container tests are easy to use and affordable, costing $20–$30. However, they’re less precise and can produce inaccurate results due to improper test conditions or the weather.

Continuous radon monitor tests are short-term tests. They’re more expensive to buy and maintain, costing more than $1,000. These monitors are typically only used by professionals. They’re more precise and read out variations in radon levels throughout the test period.

How To Perform a Radon Test

Follow the test manufacturer’s instructions when performing a radon test. Failure to do so can produce an inaccurate result.

A false-positive (actionable) result can lead you to install an unnecessary radon mitigation system. A false-negative (non-actionable) can expose you and your family to dangerous radon levels.

Here are some best practices for radon inspection tests:

Keep windows and doors closed, except for usual entry and exit from the home.
Place the test device on the home’s lowest occupiable level, either the basement or first story.
Keep the test device away from your heating and cooling supply as well as vents, exhaust fans, ceiling fans, whole-house fans, clothes dryers, and any other sources of air movement or high humidity.
Test in an area that is not a bathroom, laundry room, kitchen, or closet.
Place the test device 2–3 feet above the floor, 1–3 feet away from exterior walls, 4 inches from any object, and in a location where it won’t be disturbed.
Use the heating and cooling system in a normal manner. Don’t use whole-house fans.
Don’t perform the test during storms or high-wind events.

Radon Test Limitations

Radon tests aren’t always accurate. These factors can cause inaccurate results:

Device malfunction

Failure to follow test manufacturer’s instructions

Leaks in heating and cooling ducts, especially in crawl spaces, return ducts, and unconditioned basements

Short test periods that don’t account for weather and seasonal factors

Time of year (radon levels can be lower during summer)

Unusual weather conditions, especially high wind and high humidity

What Are Actionable Levels of Radon?

An actionable level of radon means there’s a high concentration in your home and the problem needs to be addressed. Radon is measured by picocuries per liter (pCi/L). A level between 0 and 2 pCi/L is considered non-actionable. A level between 2 and 4 pCi/L is considered marginally actionable. A level above 4 pCi/L is considered actionable.

Dealing With Radon Issues

Discuss radon mitigation measures with your builder before constructing a new home, particularly if you’re building in a Level 1 or 2 radon zone. The most common mitigation methods are installing a quality vapor retarder or sub-slab ventilation under concrete floors.

A vapor retarder, sometimes called a vapor barrier, uses a vapor barrier, fans, and piping to create a low-pressure environment that gathers radon underneath the home. Sub-slab ventilation works similarly, involving a stone layer with one or more pipes under the concrete. A fan is connected to the pipes, creating suction that routes radon from the home safely outside.

Similar mitigation measures can be installed in existing homes, especially those built on a crawl space or unfinished basement. However, installing vent pipes under an existing concrete floor could be less effective because the pipes may only capture nearby gas.

A qualified radon mitigation contractor should perform these mitigation measures. DIY radon mitigation can sometimes be effective for relatively low radon levels.

Here are some typical DIY mitigation measures:

Seal cracks in concrete floors as well as the joint between the floor and wall. Use a high-quality sealant and apply it according to the manufacturer’s instructions.
Seal leaks in heating and air conditioning ducts as well as equipment located in crawl spaces and basements. Use mastic or foil tape intended for this purpose.
Seal openings between occupied areas of your crawl space and basement. This includes openings for plumbing pipes, plumbing fixtures such as bathtubs, electrical wires, and heating and air conditioning ducts and pipes.

Our Conclusion

Radon testing and mitigation can be complicated, but it’s essential to protect you and your loved ones. We recommend hiring a qualified radon testing and mitigation professional if you aren’t comfortable with DIY projects or would rather just leave it to the pros.

Radon Resources

The following resources provide additional information on radon testing and mitigating radon risks:

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