Radon Inspection and Testing Guide

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

Written by Angela Bunt Updated 11/18/2024

All homeowners should perform a radon test, especially if you’re building or buying a home, since radon is a known carcinogen and can cause lung cancer, asthma, and other health-related issues. Testing for radon is the only way to determine if levels are normal or high. In this guide, we’ll explain the health risks of radon exposure, prevention measures, and how to inspect your home for this gas.

What Is Radon?

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

Any home can have radon, but some homes are more likely to have harmful radon levels than others. Your location is a big factor in determining how likely your home is to have a high radon level. This EPA map shows radon zones by state and county, with Zone 1 and Zone 2 having the highest potential for harmful radon levels. Neighborhoods within a county can have a higher or lower radon level than indicated on the map.

Additionally, the soil under your home could have been obtained from an area contaminated with high levels of radon, putting you and your family at risk.

In the video below, This Old House Host Kevin O’Connor talks about radon testing, safe levels, and mitigation with home technology expert Ross Trethewey.

Watch this video to see This Old House Host Kevin O’Connor and home technology expert Ross Trethewey talk about radon testing, safe levels, and mitigation.

When To Test for Radon

Certain states require homebuyers perform a radon test when they purchase their home. Many home inspectors will provide radon tests as an added service during the inspection process.

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

After your radon test, you don’t need to test again if your home has a non-harmful radon level. If your home shows a harmful level of radon, there are several ways to treat the issue.

Types of Radon Tests

There are two main types of radon tests—passive and active devices. Each has its advantages and drawbacks, and one may be better for your situation than the other.

Passive Devices

Passive devices for radon detection include alpha track detectors, charcoal canisters, and charcoal liquid scintillation detectors. After using a passive device to test for radon, you’ll return it to a laboratory for analysis.

You can purchase charcoal canisters from the National Radon Program Services website for short-term use. These and other do-it-yourself (DIY) tests are easy to use and affordable, costing $10–$50. However, they’re less precise and can produce inaccurate results due to improper test conditions or the weather.

Active Devices

Active devices require power to function and often cost more than passive testing. They include different types of continuous monitors and continuous working-level monitors. Trained testers operate these devices.

Typically, active devices test for three months to a year before you have to return them to the providing laboratory for analysis. They’re more precise and read out variations in radon levels throughout the test period.

How To Perform a DIY Radon Test

For homeowners comfortable with DIY projects, performing a radon test is straightforward. Here’s how to perform a test effecitvely.

Choose the Right Test Kit

Select a test kit approved by the National Radon Proficiency Program or the National Radon Safety Board. Short-term tests typically last two to seven days, while long-term tests span several months to a year.

Proper Test Placement

Place the test device on the lowest livable level of your home, such as the basement or first floor. Follow these placement instructions:

Keep the device two to three feet above the floor.
Keep the device at least three feet away from exterior walls.
Keep the device away from drafts, high heat, and high humidity.

Following Test Instructions

Carefully follow the device manufacturer’s instructions:

Avoid fans or other devices that move air around the home.
Keep windows and doors closed, except for normal entry and exit points.
Record the start and end times accurately.

After the test period, promptly seal and mail the device to the laboratory for analysis.

Professional Radon Testing Services

While DIY tests are convenient, professional testing offers several advantages for homeowners seeking more comprehensive results.

Benefits of Professional Testing

Professional radon inspectors use sophisticated equipment for more accurate readings. Here are a few additional benefits of professional testing:

Identify potential entry points for radon.
Offer expertise in interpreting results and suggesting mitigation strategies.
Provide detailed reports and recommendations.

Finding a Qualified Radon Inspector

To find a qualified radon professional, check for certification from the National Radon Proficiency Program or the National Radon Safety Board, and confirm they have the proper licensing if your state requires it. Additionally, ask for references and check online reviews before hiring an inspector.

Radon Test Limitations

Radon tests aren’t always 100% accurate. The following factors can cause inaccurate results:

Device malfunction
Failure to follow the 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 that you should address the problem promptly. 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 higher than 4 pCi/L is considered actionable, and you should seek professional help.

Dealing With Radon Issues

Before building a new home, discuss radon mitigation measures with your contractor, especially if you’re building in Zone 1 or Zone 2. 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 connects to the pipes, creating suction that routes radon from the home safely outside.

You can install similar mitigation measures 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.

Additionally, DIY radon mitigation can be effective for relatively low radon levels. Here are a few common 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, electrical wires, and heating and air conditioning ducts and pipes.

Preventing Radon Entry in New Construction

Incorporating radon-resistant features during construction and performing pre-construction radon testing is cost-effective and efficient for those building a new home.

Here are a few radon-resistant building techniques:

Installing a layer of clean gravel beneath the slab
Laying down a gas-permeable layer
Placing plastic sheeting on top of the gas-permeable layer
Sealing and caulking foundation cracks and openings

Testing the building site for radon before construction begins can also help determine if additional radon-resistant features are necessary.

Radon in Water: An Often Overlooked Risk

While most radon enters homes through the soil, it can also be present in well water and pose additional health risks.

Testing for Radon in Well Water

If your home uses well water, consider testing it for radon. Collect water samples and send them to a certified laboratory for analysis.

Water Treatment Options

If you detect high levels of radon in your water, you can install an aeration system that removes radon from the water before it enters your home. You can also purchase granular activated carbon filters for smaller water systems.

Legal and Real Estate Radon Considerations

Radon can have implications beyond health concerns, affecting property transactions and values. Many states require sellers to disclose known radon issues during real estate transactions. Familiarize yourself with your state’s laws regarding radon disclosure.

Additionally, high radon levels can affect property values. Homes with functioning mitigation systems are often viewed favorably, demonstrating proactive management of the issue.

Our Conclusion

Radon testing and mitigation is essential to determine the radon levels in your home and protect you and your loved ones from adverse health effects. We recommend hiring a qualified radon testing professional to test radon before building or buying a home if you aren’t comfortable with DIY testing.

Radon Resources

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

Frequently Asked Questions About Radon Testing

Is radon testing really necessary?

Yes, radon testing is necessary for all homeowners, as radon exposure can have hazardous consequences. The EPA recommends that all homeowners test their homes for radon.

What houses are most at risk for radon?

While any home could be at risk of having high levels of radon, some homes are more likely to have harmful radon levels than others. The EPA website provides a map of radon zones—homes located in Zone 1 or Zone 2 are at high risk of radon exposure.

Should I walk away from a house with radon?

While it’s important to know whether or not a home has unsafe levels of radon, high radon levels don’t mean that you need to walk away from purchasing a particular home. There are several options to successfully deal with radon and make a home safe for all inhabitants.

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