About Radon



Home Buyer’s and Seller’s Guide to Radon

Why do you need to test for radon?

Radon is a cancer-causing, radioactive gas.

Testing is the only way to find out your home’s radon levels. The EPA and the Surgeon General recommend testing all homes below the third floor for radon.

You can fix a radon problem.

If you find that you have high radon levels, there are ways to fix a radon problem. Even very high levels can be reduced to acceptable levels.

Radon has been found in homes all over the U.S.

Radon is a radioactive gas that has been found in homes all over the United States. It comes from the natural breakdown of uranium in soil, rock and water, and gets into the air you breathe. Radon typically moves up through the ground to the air above, and into your home through cracks and other holes in the foundation. Radon can also enter your home through well water. Your home then traps radon inside, creating levels higher than present outdoors.

Any home can have a radon problem, including new and old homes, well-sealed and drafty homes, and homes with or without basements. In fact, you and your family are most likely to get your greatest radiation exposure at home, because that is where you spend most of your time.

Nearly 1-in-15 homes in the United States is estimated to have an elevated radon level of (4 pCi/L or more).  Elevated levels of radon gas have been found in homes in every state, and commonly in this region.

The EPA and the Surgeon General recommend that you test your home.

You cannot predict radon levels based on state, local, or neighborhood radon measurements.  Do not rely on radon test results taken in other homes in the neighborhood to estimate the radon level in your home.  Homes which are next to each other can have different radon levels.  Testing is the only way to find out what your home’s radon level is.

U.S. Surgeon General’s
Health Advisory

“Indoor radon gas is the second-leading cause of lung cancer in the United States, and breathing it over prolonged periods can present a significant health risk to families all over the country.  It’s important to know that this threat is completely preventable.  Radon can be detected with a simple test, and fixed through well-established venting techniques.” 

Radon is a cancer-causing, radioactive gas.

Radon is the second leading cause of lung cancer in the United States today.  When you breathe air containing radon, you increase your risk of getting lung cancer.  If you smoke and your home has high radon levels, your risk of lung cancer is especially high.

You cannot see, smell or taste radon. But it still may be a problem in your home.

Your radon measurement will give you an idea of your risk of getting lung cancer from radon. Your chances of getting lung cancer from radon depend mostly on:

  • your home’s radon level; 
  • the amount of time you spend in your home; and
  • whether you are a smoker or have ever smoked.

Smoking combined with radon is an especially serious health risk. If you smoke or are a former smoker, the presence of radon greatly increases your risk of lung cancer. If you stop smoking now and lower the radon level in your house, you will reduce your lung cancer risk.

Based on information contained in the National Academy of Sciences’ 1998 report, The Health Effects of Exposure to Indoor Radon, your radon risk may be somewhat higher than shown, especially if you have never smoked.  It’s never too late to reduce your risk to lung cancer.  Don’t wait to test and fix a radon problem.  If you are a smoker, stop smoking.

Go to the Radon Risk Comparison Charts

  • If you are buying a home or selling your home, have it tested for radon.  
  • For a new home, ask if radon-resistant construction features were used and if the home has been tested. If test results cannot be produced, test.
  • Take steps to prevent device interference when conducting a radon test.
  • Fix the home if the radon level is 4 picoCuries per liter (pCi/L) or higher.  
  • Radon levels less than 4 pCi/L still pose a risk, and in many cases, may be reduced.

The EPA estimates that radon causes about 21,000 lung cancer deaths per year.

There is certainty about radon health risks. We know more about radon risks than most other cancer-causing substances. This is because estimates of radon risks are based on data from human studies on underground miners. Additional studies on more typical populations are underway.

If your home has not yet been tested for radon…

The EPA recommends that you test your home before putting it on the market and, if necessary, lower your radon levels. Save the test results and all information you have about steps that were taken to fix any problems. This could be a positive selling point. 

If you have already tested your home for radon, review the Radon Testing Checklist to make sure that the test was done correctly.  If so, provide your test results to the buyer.

No matter what kind of test you took, a potential buyer may ask for a new test, especially if:

  • the Radon Testing Checklist items were not met;
  • the last test is not recent, (e.g., within two years);
  • a passive test was performed, rather than an active monitor test.
  • you have renovated or altered your home since you tested; or
  • the buyer plans to live in a lower level of the house than was tested, such as a basement suitable for occupancy but not currently lived in.

A buyer may also ask for a new test if your state or local government requires disclosure of radon information to buyers.

The EPA recommends that you know what the indoor radon level is in any home you are considering buying.

If the home has not yet been tested, you should have the house tested.

If the home has a radon-reduction system, ask the seller for information they have about the system.

If the home has already been tested for radon…

Before you accept the seller’s test, you should determine the results of previous testing by finding out:

  • who conducted the previous test (the homeowner, a radon professional, or some other person);
  • where in the home the previous test was taken, especially if you may plan to live in a lower level of the home.  For example, the test may have been taken on the first floor.  However, if you want to use the basement as living space, test there, too;
  • what, if any, structural changes, alterations, or changes in the heating, ventilation, and air conditioning (HVAC) system have been made to the house since the test was done.  Such changes may affect radon levels.

If you decide that a new test is needed, discuss it with the seller as soon as possible. 

If the home has not yet been tested for radon…

Make sure that a radon test is done as soon as possible. Consider including provisions in the contract specifying:

  • where the test will be located;
  • who should conduct the test;
  • what type of test to do;
  • when to do the test;
  • how the seller and the buyer will share the test results and test costs (if necessary); and
  • when radon mitigation measures will be taken, and who will pay for them.

 If you decide to finish or renovate an unfinished area of the home in the future, a radon test should be taken before starting the project, and after the project is finished. Generally, it is less expensive to install a radon-reduction system during renovations rather than afterward.

Build a radon-resistant home.

Radon-resistant techniques work.  When installed properly and completely, these simple and inexpensive passive techniques can help to reduce radon levels.  In addition, installing them at the time of construction makes it easier to reduce radon levels further if the passive techniques don’t reduce radon levels below 4 pCi/L.  

Radon-resistant techniques may also help to lower moisture levels and those of other soil-gases.  

Radon-resistant techniques:


-Make upgrading easy:  Even if built to be radon-resistant, every new home should be tested for radon after occupancy.  If you have a test result of 4 pCi/L or more, a vent fan can easily be added to the passive system to make it an active system, and further reduce radon levels.


-Are cost-effective:  Building radon-resistant features into the house during construction is easier and cheaper than fixing a radon problem from scratch later.  Let your builder know that radon-resistant features are easy to install using common building materials.


-Save money:  When installed properly and completely, radon-resistant techniques can also make your home more energy-efficient and help you save on your energy costs.

What are radon-resistant features?

Radon-resistant features may vary for different foundations and site requirements.  If you’re having a house built, you can learn about the EPA’s Model Standards (and architectural drawings) and explain the techniques to your builder.  If your new house was built (or will be built) to be radon-resistant, it will include these basic elements:

  1. gas-permeable layer:  This layer is placed beneath the slab or flooring system to allow the soil gas to move freely underneath the house.  In many cases, the material used is a 4-inch layer of clean gravel.  This gas-permeable layer is used only in homes with basement and slab-on-grade foundations; it is not used in most homes with crawlspace foundations.  
  2. plastic sheeting:  Plastic sheeting is placed on top of the gas-permeable layer and under the slab to help prevent the soil gas from entering the home.  In crawlspaces, the sheeting (with seams sealed) is placed directly over the crawlspace floor.  
  3. sealing and caulking:  All below-grade openings in the foundation and walls are sealed to reduce soil-gas entry into the home.  
  4. vent pipe:  A 3- or 4-inch PVC pipe (or other gas-tight pipe) runs from the gas-permeable layer through the house to the roof to safely vent radon and other soil gases to the outside.  
  5. junction boxes:  An electrical junction box is included in the attic to make the wiring and installation of a vent fan easier, if, for example, you decide to activate the passive system if your test results show an elevated radon level (4 pCi/L or more).  A separate junction box is placed in the living space to power the vent-fan alarm.  An alarm is installed along with the vent fan to indicate when the vent fan is not operating properly.

In a new home, the cost to install passive radon-resistant features during construction is usually between $650 to $1,000. A qualified mitigator will charge about $500 to add a vent fan to a passive system, making it an active system and further reducing radon levels. 

Radon testing is easy and the only way to find out if you have a radon problem in your home.

Since you cannot see or smell radon, special equipment is needed to detect it. 

Active radon-testing devices continuously measure and record the amount of radon and its decay products in the air. This device provides a report of this information, which can reveal any unusual or abnormal swings in the radon level during the test period. In addition,  this device is specifically designed to deter and detect test interference. 

We use the AirThings Corentium Pro.

Although these tests come at a cost, they ensure a more reliable result.


During a radon test:

  • Maintain closed-house conditions during the entire time of a short-term test, especially for tests shorter than one week.
  • Operate the home’s heating and cooling systems normally during the test. For tests lasting less than one week, operate only air-conditioning units which re-circulate interior air.
  • Do not disturb the test device at any time during the test.

Preventing or Detecting Test Interference

There is a potential for test interference in real estate transactions. There are several ways to prevent or detect test interference:

  • Our device continuously records radon or decay-product levels to detect unusual swings.
  • Our device has a built-in motion detector to determine whether the test device has been moved or if testing conditions have changed.
  • Our device records the barometric pressure to identify weather conditions which may have affected the test.
  • Our device records the temperature and humidity to help assess whether doors and windows have been opened during the test. 
  • Apply tamper-proof seals to windows to ensure closed-house conditions.
  • Have the seller/occupant sign a non-interference agreement.

All radon tests should be taken for a minimum of 48 hours. 

Your radon test results will be reported in picoCuries per liter of air (pCi/L). 

Roughly 0.4 pCi/L of radon is normally found in the outside air.

The average indoor radon level is estimated to be about 1.3 pCi/L.

The EPA recommends you fix your home if your radon level is 4 pCi/L or higher. 

However, the EPA believes that any radon exposure carries some risk; no level of radon is safe. Even radon levels below 4 pCi/L pose some risk.  You can reduce your risk of lung cancer by lowering your radon level.

The U.S. Congress has set a long-term goal that indoor radon levels be no more than outdoor levels. While this goal is not yet technologically achievable for all homes, radon levels in many homes can be reduced to 2 pCi/L or below.

When the results are close to 4 pCi/L, for example, if the average of two short-term tests is 4.1 pCi/L, there is about a 50% chance that the year-round average is below 4 pCi/L. In this case, seasonal testing is recommended.

In most cases, a system with a vent pipe and fan is used to reduce radon.  

These “sub-slab depressurization” systems do not require major changes to your home. These systems prevent radon gas from entering the home from below the concrete floor and from outside the foundation. 

Similar systems can also be installed in homes with crawlspaces. Radon mitigation contractors may use other methods that may also work in your home. The right system depends on the design of your home and other factors. 

If elevated levels are found during the real estate transaction, the buyer and seller should discuss the timing and costs of the radon reduction.  The cost of making repairs to reduce radon levels depends on how your home was built and other factors. Most homes can be fixed for about the same cost as other common home repairs, such as painting or having a new hot water heater installed. The average cost for a contractor to lower radon levels in a home may range from $1,800 to about $4,500.

 If you are planning any major renovations, such as converting an unfinished basement area into living space, it is especially important to test the area for radon before you begin, and after the project is finished. 

Generally, it is less expensive to install a radon-reduction system during renovations rather than afterward.

If your test results indicate an elevated radon level, radon-resistant techniques can be inexpensively included as part of the renovation. Major renovations can change the level of radon in any home.  Test again after the work is completed.

You should also test your home again after it is fixed to be sure that radon levels have been reduced. In addition, it is a good idea to re-test your home sometime in the future to be sure radon levels remain low.

Select a qualified radon-reduction contractor to reduce the radon levels in your home.  

Any mitigation measures taken or system installed in your home must conform to your state’s regulations.  

The EPA recommends that the mitigation contractor review the radon measurement results before beginning any radon-reduction work.  Test again after the radon mitigation work has been completed to confirm that previous elevated levels have been reduced.  

What can a qualified radon-reduction contractor do for you?

A qualified radon-reduction (mitigation) contractor should be able to:

  • review testing guidelines and measurement results, and determine if additional measurements are needed; 
  • evaluate the radon problem, and provide you with a detailed, written proposal on how radon levels will be lowered; 
  • design a radon-reduction system; 
  • install the system according to EPA standards, or state or local codes; and
  • make sure the finished system effectively reduces radon levels to acceptable levels.

Choose a radon-mitigation contractor to fix your radon problem just as you would for any other home repair.  You may want to get more than one estimate.  Ask for and check their references.  Make sure the person you hire is qualified to install a mitigation system.  Some states regulate or certify radon-mitigation services providers.

Be aware that a potential conflict of interest exists if the same person or firm performs the testing and installs the mitigation system.  Some states may require the homeowner to sign a waiver, in such cases. Contact your state radon office for more information.

The radon in your home’s indoor air can come from two sources:  the soil and your water supply. 

Compared to radon entering your home through water, airborne radon entering your home through soil is a much larger risk.  If you’ve tested for radon in air and have elevated radon levels, and your water comes from a private well, have your water tested.  The devices and procedures for testing your home’s water supply are different from those used for measuring radon in air.

The radon in your water supply poses an inhalation risk and an ingestion risk.  Research has shown that your risk of lung cancer from breathing radon in the air is much larger than your risk of stomach cancer from swallowing water with radon in it.  Most of your risk from radon in water comes from radon released into the air when water is used for showering and other household purposes.

Problematic Radon in your home’s water is less likely when its source is surface water.  Radon in water is more likely when its source is ground water, e.g., a private well or a public water supply system that uses ground water.  Some public water systems treat their water to reduce radon levels before it is delivered to your home.  If you are concerned that radon may be entering your home through the water, and your water comes from a public water supply, contact your water supplier.

If you’ve tested your private well and have radon in your water supply, it can be treated in one of two ways. 

  • Point-of-entry treatment can effectively remove radon from the water before it enters your home.  Point-of-entry treatment usually employs either granular activated-carbon (GAC) filters, or aeration devices.  While GAC filters usually cost less than aeration devices, filters can collect radioactivity and may require a special method of disposal.
  • Point-of-use treatment devices remove radon from your water at the tap, but only treat a small portion of the water you use, e.g., the water you drink.  Point-of-use devices are not effective in reducing the risk of breathing radon released into the air from all water used in the home.