High radon levels

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2 pCi/L

4 pCi/L

00 Bq/m³274 Bq/m³4148 Bq/m³6222 Bq/m³8296 Bq/m³10+370 Bq/m³

• Below 2 pCi/L (below 74 Bq/m³)Below both of EPA's guidance levels.
• 2 to 4 pCi/L (74 Bq/m³ to 148 Bq/m³)EPA recommends considering a fix when the level is between 2 and 4 pCi/L.
• At or above 4 pCi/L (148 Bq/m³ and up)EPA recommends fixing a home when the radon level is 4 pCi/L or higher.

Unsafe radon levels: why EPA draws no safe line

People ask which radon levels are unsafe. EPA's action level marks where it recommends fixing a home, not where risk begins: EPA says radon levels less than 4 pCi/L still pose a risk and in many cases may be reduced. CDC says there is no known safe level of radon and that you should always aim to have the lowest level. EPA's Home Buyer's and Seller's Guide states the principle in one line:

WHO reports that radon levels in buildings such as homes, schools and offices can vary substantially, from 10 Bq/m3 to more than 10 000 Bq/m3, while the average outdoor level varies from 5 Bq/m3 to 15 Bq/m3. EPA estimates the average indoor radon level in the U.S. at about 1.3 pCi/L, with about 0.4 pCi/L normally found in outside air.

Elevated levels are not rare. EPA estimates that nearly one out of every 15 homes in the United States has an elevated radon level, which EPA defines there as 4 pCi/L or more, and says high radon levels have been found in every state. They also vary sharply from house to house: EPA says homes next to each other can have different indoor radon levels, and that you cannot predict radon levels based on state, local and neighborhood measurements. The radon map and location reports are useful context for an area, not a reading for a house.

What causes high radon levels

EPA says radon from soil gas is the main cause of radon problems; it moves up through the ground and into the home through cracks and other holes in the foundation, and the home traps it inside. WHO lists what sets the concentration in a building:

• The local geology, for example the uranium content and permeability of the underlying rocks and soils.
• The routes available for radon to pass from the soil into the building.
• Radon given off by building materials.
• The rate of exchange between indoor and outdoor air, which depends on the construction of the building, the ventilation habits of the occupants and the air-tightness of the building.

EPA adds that any home may have a radon problem: new and old homes, well-sealed and drafty homes, and homes with or without basements. Local geology, construction materials and how the home was built are among the factors EPA names.

Radon is not spread evenly through a house, and it does not hold still over time. Where and when a test runs changes what it finds, which is why EPA is specific about both.

High levels of radon in basement

WHO says radon levels are usually higher in basements, cellars and living spaces in contact with the ground, and CDC notes that levels are often higher in basements and lower levels. EPA's advice is to test the lowest lived-in level: the basement if it is used frequently, otherwise the first floor. For a home sale, EPA asks for the lowest level that could be used regularly, finished or unfinished, because a buyer may live in a lower area than the seller did. If you start using the basement, retest on that level.

Planning to finish a basement? EPA says it is especially important to test the area before you begin a major renovation such as converting an unfinished basement into living space. If the result indicates a radon problem, radon-resistant techniques can be inexpensively included as part of the renovation, and because major renovations can change the radon level in any home, EPA says to test again after the work is completed.

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1. 1Cracks in solid floors
2. 2Construction joints
3. 3Cracks in walls
4. 4Gaps in suspended floors
5. 5Gaps around service pipes
6. 6Cavities inside walls
7. 7The water supply

Upstairs and above the ground floor

Higher floors are not automatically low. WHO notes that considerable radon concentration can also be found above the ground floor. EPA and the Surgeon General recommend testing all homes below the third floor.

When are radon levels highest?

Radon levels vary rather than peak at a single time. WHO says radon concentrations vary within a building from day to day and from hour to hour, and EPA says radon levels tend to vary from day to day and season to season. That is why EPA says a short-term test is less likely than a long-term test to tell you your year-round average, and why WHO says it is preferable to estimate the annual mean from measurements of at least 3 months. More on timing in when are radon levels highest.

This is one of the most common questions behind a search for high radon levels. A reading of 4.8 pCi/L, about 178 Bq/m3 by Radon411's conversion, is above EPA's 4 pCi/L action level, so it is high enough to act on. What to do next depends on what kind of test produced it.

Short-term results close to 4 pCi/L are the least certain. EPA gives an example: if the average of two short-term tests is 4.1 pCi/L, there is about a 50 percent chance that the year-round average is somewhat below, or above, 4 pCi/L. It also says that the higher your short-term results, the more certain you can be that you should fix your home. The result interpreter walks through your own number.

Is a radon level of 5 bad?

A confirmed 5 pCi/L is above EPA's action level, so EPA recommends fixing the home. EPA's steps keep the word immediately for first results more than twice the action level, so a single 5 pCi/L short-term result calls for a follow-up test first. See is a radon level of 5 bad and what 5 pCi/L means.

There is no single level at which radon becomes dangerous, because the risk rises with the level from the start. EPA's action level page says there is no known safe level of exposure to radon, and CDC says there is no known safe level of radon. What EPA does give is a chart of lifetime risk at each level, set beside familiar risks, so the size of a high reading can be seen.

These are EPA's population estimates for a lifetime at that level, not a forecast for any person, and they show how much smoking changes the picture. The urgency of a high level is about acting, not alarm: the Surgeon General's advisory says that at a radon level of 4 pCi/L or more, take steps to remedy the problem as soon as possible, and EPA's testing steps call for a second short-term test immediately when a first result is more than twice the action level. EPA's Home Buyer's and Seller's Guide adds that you will reduce your risk of lung cancer when you reduce radon levels, even if you have lived with an elevated radon level for a long time.

Is it safe to live in a house with high radon?

The risk builds over years, and the answer is to confirm the level and lower it. Until a system is installed, CDC's radon page lists interim steps, below. See is it safe to live in a house with radon.

Searches for a specific number, such as a radon level of 6, 8, 20 or 30 pCi/L, all have the same answer in EPA's guidance: the number is above the action level, and what to do next depends on whether it came from a single short-term test. Here is how EPA's steps apply to each, with the Bq/m3 figures converted by Radon411 at 37 Bq/m3 per pCi/L.

CDC's testing page states the same follow-up in its own words: if you used a short-term test, take a second test using either a short-term or long-term test, and if you use a second short-term test, calculate the average of the two results. For a long-term test, EPA says to fix the home if the result is 4 pCi/L or more. To read a specific number, use the result interpreter.

EPA's Citizen's Guide describes a sequence rather than a verdict on one number. These are its three steps:

1. 1

   Take a short-term test

   If the result is at or above the 4 pCi/L action level, take a follow-up test to be sure.

2. 2

   Follow up

   Take a long-term test for a better understanding of your year-round average, or a second short-term test if you need results quickly. The higher the first result, the more certain you can be that a short-term follow-up is the right choice. If the first result is more than twice EPA's 4 pCi/L action level, take the second short-term test immediately.

3. 3

   Decide

   After a long-term follow-up, fix the home if the result is at or above 4 pCi/L. After a second short-term test, consider fixing if the average of the two is at or above 4 pCi/L; the higher the results, the more certain you can be.

Testing is the only way to know the radon level in a specific building. A certified measurement professional can run the follow-up for you, and how to test for radon covers placement and devices.

A mitigation system takes time to arrange. CDC's radon page passes on steps the U.S. Department of Housing and Urban Development recommends, with a caution about each:

EPA says there are several proven methods to reduce radon in homes, but the one primarily used is a vent pipe system and fan that pulls radon from beneath the house and vents it to the outside. EPA's Home Buyer's and Seller's Guide calls these sub-slab depressurization systems and says they do not require major changes to your home; similar systems can be installed in homes with crawl spaces. Sealing cracks and openings is a basic part of most approaches, but EPA does not recommend sealing alone, which has not been shown to lower radon levels significantly or consistently.

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1. 1Soil gas drawn from beneath the slab
2. 2Suction point through the slab
3. 3Vent pipe
4. 4Fan, outside the living space
5. 5Discharge above the roofline

EPA says radon reduction systems work, that some can reduce radon levels by up to 99%, and that even very high levels can be reduced to acceptable levels. It also says most homes today can be reduced to 2 pCi/L or below. The right system depends on the design of the home and other factors, so the contractor matters:

• Use a contractor trained to fix radon problems. Lowering high radon levels requires technical knowledge and special skills.
• The system must conform to your state's regulations; where there are none, EPA recommends EPA's most current voluntary consensus-based standards.
• EPA recommends the contractor review your measurement results before starting, and provide a detailed, written proposal.
• Get references and more than one estimate, as for any home repair.
• EPA flags a potential conflict of interest when the same person or firm performs the testing and installs the system.
• Some states run credentialing programs for radon service providers. EPA lists CA, CO, CT, FL, IL, IN, IA, KS, KY, ME, MN, NE, NH, NJ, OH, PA, RI, UT, VA and WV.

The directory lists mitigation professionals, and radon mitigation explains the process from proposal to post-installation test.

What fixing high radon costs

CDC says the cost of reducing radon in your home can vary widely, that cost depends on how your home was built and the extent of the radon problem, and that most homes can be fixed for about the same cost as other common home repairs. Get one or more estimates from qualified contractors; CDC warns that contractors who do not specialize in radon reduction could make the problem worse. See radon mitigation cost.

Radon still high after mitigation

EPA says to test again after the mitigation work to confirm that the elevated level has been reduced, and recommends that this test be done by an independent, qualified radon tester. A qualified contractor should make sure the finished system effectively reduces radon levels to acceptable levels. Most soil suction systems include a monitor that indicates whether the system is operating properly; if the vent fan is not operating properly, EPA says to have it repaired and then test. After that, EPA suggests retesting every two years to be sure levels remain low.

EPA recommends that you know the indoor radon level in any home you consider buying. Ask the seller for their test results; if the home has a radon-reduction system, ask for any information about it; if the home has not been tested, have it tested. Before accepting a seller's test, EPA says to check who ran it, where in the home it was taken, and whether structural, heating, ventilation or air-conditioning changes have been made since.

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If you are testing in a real estate transaction and you need results quickly, any of the following three options for short-term tests are acceptable in determining whether the home should be fixed.

1. Option 1. Two tests at the same time

   Passive

   Take two short-term tests at the same time in the same location for at least 48 hours.

   What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

   Two tests taken at the same time (simultaneous) would improve the precision of this radon test.

2. Option 2. One test, then a second

   Passive

   Take an initial short-term test for at least 48 hours. Immediately upon completing the first test, do a second test using an identical device in the same location as the first test.

   What to do nextFix the home if the average of the two tests is 4 pCi/L or more.

   One test followed by another test (sequential) would most likely give a better representation of the seasonal average.

3. Option 3. A continuous monitor

   Active

   Test the home with a continuous monitor for at least 48 hours.

   What to do nextFix the home if the average radon level is 4 pCi/L or more.

   Both active and passive devices may have features which help to prevent test interference.

Any real estate test for radon should include steps to prevent or detect interference with the test device. Your state radon office can help you decide which option is best.

Buying house with high radon: what to put in the contract

EPA's Home Buyer's and Seller's Guide suggests the purchase contract specify:

• Where the test will be located, and who should conduct it.
• What type of test to do, and when to do it.
• How the seller and the buyer will share the test results and test costs, if necessary.
• When radon mitigation measures will be taken, and who will pay for them.

If elevated levels are found during the transaction, EPA says the buyer and seller should discuss the timing and costs of radon reduction. A high result is a known, fixable problem: EPA's Citizen's Guide says that where radon problems have been fixed, home sales have not been blocked or frustrated. See buying a house: radon guide and should I buy a house with radon.