Everything You Need to Know About Radon

Everything You Need to Know About Radon

You’ve found your home, you’ve written an offer, it’s been accepted and you are “Under Contract”. Now it’s time to find out what the real condition of this property is. In order to accomplish this you are going to want to do a Property Inspection. When you schedule the inspection, you should be asked to decide if you want the inspector to perform a radon test. In all but the rarest cases the answer should be yes.

What is Radon?

Radon is a naturally occurring, inert, odorless, colorless, radioactive gas. It is formed by the radioactive decay of uranium in rock, soil, and water. So, without a test, there is no way to know if your home has it.

What does it do?

Radon is right behind cigarettes as the second leading cause of lung cancer. Radon is associated with 15,000 to 22,000 lung cancer deaths in the United States annually.

Here is a good description, written by the National Cancer Institute of what Radon does to cause cancer.

Radon decays quickly, giving off tiny radioactive particles. When inhaled, these radioactive particles can damage the cells that line the lung. Long-term exposure to radon can lead to lung cancer, the only cancer proven to be associated with inhaling radon. There has been a suggestion of increased risk of leukemia associated with radon exposure in adults and children; however, the evidence is not conclusive.

Radon is actually a controversial topic and while there are many credible sources that question the effects radon has on human beings, the evidence and research that it is harmful is too overwhelming for us to ignore, especially when representing home buyers. Here is a list of organizations that state Radon is a health threat:

      • U.S. Surgeon General
      • American Medical Association
      • American Lung Association
      • Centers for Disease Control
      • National Cancer Institute
      • National Academy of Sciences
      • Environmental Protection Agency

Testing and Measuring

Here’s the science of radon, levels are measured and talked about in terms of “Picocuries” this is an international unit of radioactivity that is defined as 1 Ci = 3.7×1010 decays per second. This is approximately the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Pierre and Marie Curie, for whom the unit was named.

The important number to remember for the purposes of radon in a home is 4 pCi/L (picocuries per liter). This is the number above which the EPA recommends mitigation.

It’s important to note that we often hear about higher acceptable levels in other countries, the point being the US is “unreasonably” low. This might be the case but as far as the United States is concerned 4 pCi/L is the magic number.

Testing for Radon is important, especially here along the front range because radon is prevalent in the entire State of Colorado but especially high right here in El Paso County.

The Environmental Protection Agency (EPA) produces a “Radon Map”. This map categorizes areas into three zones to assess radon potential. All of El Paso County is in “Zone 1”

  • Zone 1- Highest Potential: These are counties that have a predicted average indoor radon screening level greater than 4 pCi/L (picocuries per liter)
  • Zone 2- Moderate Potential: These are counties that have a predicted average indoor radon screening level between 2 and 4 pCi/L
  • Zone 3- Low Potential: These are counties have a predicted average indoor radon screening level less than 2 pCi/L

The criteria used to develop this assessment are as follows:

      1. Indoor radon measurements
      2. Geology
      3. Aerial radioactivity
      4. Soil permeability
      5. Foundation type

As far as testing methods are concerned, most certified home inspectors will use a handful of different testing methods. Some require post inspection processing therefore requiring a wait to see the results. It’s important to keep track of your inspection deadlines, you don’t want to end up with elevated radon levels but ask for mitigation after your inspection objection deadline.

How does radon get into a house

The primary entry point for radon into the home is through the foundation. If you have a basement, the gas can seep through small cracks and voids in the slab. Crawl Spaces are generally left uncovered thus providing no barrier for radon gases. Sometimes radon enters the home through well water.


There are a handful of different methods used to mitigate radon from a home. The most popular method here along the front range of Colorado is Active soil depressurization (ASD).

Active soil depressurization (ASD) essentially keeps radon gas from entering the home by changing the pressure differential, essentially depressurizing the force that pushes the gas from below the foundation slab or crawlspace into the home. Radon is drawn from beneath the slab by an exhaust fan that vents the radon gas through a PVC pipe up and over the roof of the home to the outdoor air where it dilutes into the atmosphere.

It’s important that radon mitigation systems vent above the properties roof. Since radon gas is heavier than air the possibility exists that the gas can be picked up and redistributed through the homes HVAC system. By venting above the roof the concentration of gas falls off significantly before it has the opportunity to be reintroduced.

It’s important to note that the active soil depressurization system is a separate system and is not related to your homes HVAC or any other system except that it draws a slight low voltage feed from your electric system. So, the cost to operate an ASD system is low as well. The system fans typically use 90 watts per fan. The cost to operate one of these units is approximately $25 to $45 per year.

The cost of installation varies based on the size of the home and the type of foundation. Here along the front Range of Colorado, systems run from $800 on the low end to $2,500 on the high end. Newer homes with perimeter drains tend to be easier for installation of mitigation systems and therefore cost less.

We test for radon during the inspection because it’s generally something we want the seller to pay for. In some cases the buyer may be willing to accept the cost of mitigation, this generally has to do with the purchase price and terms.

If the seller ends up installing the system it’s important to get documentation about who installed the system what the numbers look like on the retest and what the warranty is. All of this should be wrapped up prior to closing.

Frequently Asked Questions about radon:

Can radon levels change over time?

    • Yes, changes in temperature, Moisture and Dryness can cause the uranium levels to rise which results in an increase in radon levels. If the ground around your home becomes saturated, frozen or covered with snow, it keeps the radon in the ground not allowing it to escape. Wind can also change the pressure around your home, which could cause radon to diffuse into your home. It is recommended not to test during severe weather or high winds.

How often should we test?

    • If you have a system in your homes the EPA and IEMA recommend that you test every two years. How long do Mitigation Systems Last? Usually, the manufacturer warrants the fan for 5 years. The national average for the life of a fan is 11 years. Some last as long as 20 years.

Should we test for radon if a mitigation system is present?

    • Yes, if it has been 2 years since it was installed.

What is the cost of operating a mitigation system?

    • $25-$45 a year.

What is a Picocurie?

    • This is an international unit of radioactivity that is defined as 1 Ci = 3.7×1010 decays per second. This is approximately the activity of 1 gram of the radium isotope 226Ra, a substance studied by the pioneers of radiology, Pierre Curie and Marie, for whom the unit was named.

What’s the fastest way to test?

      • The quickest way to test is with a short-term test. These kits remain in your home for two days to 90 days, depending on the device.


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