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Do Crawl Spaces Have High Radon Levels?

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When buying or selling a home, you might hear questions about having radon testing performed. Of course, it’s a good idea, and in the long run, you’ll be happy you did. But aside from testing the ground floor of your home, make sure that the crawl space is checked too. The crawl space might not cross your mind, but it is one of the main gateways for radon to get into your home.

There are a few things you need to learn about radon and how it can affect a crawl space, including:

  • Is Radon Dangerous?
  • How Does Radon Get Into Crawl Spaces?
  • Are Crawl Spaces More Prone to Radon Infiltration?
  • When Should You Test for Radon?
  • What Can You Do to Mitigate Radon in Crawl Spaces?

Ready to learn more? Grab a pen and paper and continue reading!

Is Radon Dangerous?

Radon is an odorless, colorless radioactive gas that naturally occurs in the atmosphere. In outdoor settings, the gas is not considered dangerous. It disperses relatively quickly and isn’t regarded as hazardous to your health.

The danger comes when it is "trapped indoors." According to The Environmental Protection Agency (EPA), once levels reach 4 picocuries/liter or higher, the risks to your health become greater. In fact, it's actually one of the key causes of lung cancer in the entire United States, with thousands of people dying from it each year.

How Does Radon Get Into Crawl Spaces?

Radon is a gas that releases from naturally decaying uranium found in almost every soil type. Your home can become contaminated as the gas seeps through minute cracks or holes in your foundation. As radon seeps in, it becomes trapped inside which causes the levels to rise.

The building materials used may also emit radon into the air. However, even when building materials give off radon, they are at low levels and are not considered hazardous. If you have a well on your property, it could also contribute to higher than normal levels.

Are Crawl Spaces More Prone to Radon Infiltration?

Like basements, crawl spaces are especially prone to radon issues because of their location below the home and the fact that many have dirt floors. Think of your crawl space’s dirt floor like a window. It's always open and exposing your home to the elements. Radon and other gases come into your home through the ‘open window,’ i.e. dirt, and then become trapped in your home.

Homes in areas where low pressure is prevalent may see a more significant increase in radon levels. Days with heavy rain and wind tend to cause levels to rise because of the barometric pressure. Higher pressure days, however, result in less radon in the crawl space of your home.

Without a protective barrier to trap and ventilate the gas, it can quickly build up to dangerous levels. It then seeps into your home from the crawl space, making it a hazardous place to live.

When Should You Have Radon Testing in Crawl Spaces?

There is no magic timetable for when you should test your home’s crawl space for radon. As a general rule, it's best to have the entire house tested, especially if it's one you are looking to purchase. However, suppose you live in an area with known high radon levels, such as in the northeastern part of the United States. In that case, you can request a test be performed during the inspection process.

If you haven't had your home tested in a while, it wouldn't be a bad idea to research a local company to come out and perform the test for you. For more information on radon testing, check out How is Radon Testing Done in a Home?

Mitigating Radon From Your Crawl Space

Your crawl space is especially prone to radon gas because of where it's located. Luckily, there are several different methods for mitigating it, the most common one being Crawl Space Sub-Membrane Depressurization. The first step is cutting off the source.

Then, a fan and pipe are installed to help vent radon outside. The fan helps to equalize the crawl space air pressure with the indoor air pressure on the first floor. The pipe venting gas outside runs along the side of the house to the roof. The placement ensures that radon is pushed away from your home.

In combination with the ventilation system, your crawl space floor may be covered as well. The covering acts as a barrier between the soil and your home. As a result, it allows the ventilation system to work more effectively.


Crawl spaces are the prime locations to find radon-laden air. By understanding the dangers of radon and how it gets into your home’s crawl space, you can more effectively combat the situation. Also, because radon does carry health & safety risks, it's in yours and your family's best interests to seek outside help getting rid of it. Above all, safety first!