Radon in homes

EPA names two main sources for the radon in a home's indoor air, the soil and the water supply, and one minor one, building materials. The weight EPA gives each is very different.

What causes radon in homes: the pressure difference

EPA's Consumer's Guide explains why a house pulls radon in rather than simply sitting on top of it. Air pressure inside a home is usually lower than the pressure in the soil around its foundation. Because of that difference, the home acts like a vacuum, drawing radon in through foundation cracks and other openings. Once inside, EPA says, the home traps radon, where it can build up.

If your water comes from a private well and an air test shows a radon problem, EPA advises having the water tested too. The radon in water guide explains how.

What pulls radon in: stack effect, exhaust fans and ducts

EPA's builder guide, Building Radon Out, names the everyday forces behind the pressure difference. When air is exhausted, outside air enters the house to replace it, and some of the replacement air comes from the underlying soil and can contain radon.

No kind of house is safe by type, and no kind is doomed. Building Radon Out says four main factors drive radon entry into homes, and all of these factors exist in most homes throughout the country: uranium is present in the soil nearly everywhere in the United States; the soil is permeable enough to let radon migrate in; there are pathways for the radon to enter; and an air pressure difference draws it in. It concludes that because radon can literally be sucked into a home, any home can potentially have a radon problem, and that all conventional house construction types have been found to have radon levels exceeding the action level of 4 pCi/L.

The last row is a prediction for an area, not a reading of any house. EPA's zone map says homes with elevated levels of radon have been found in all three zones, that all homes should be tested for radon, and that the map should not be used to determine if a home in a given zone should be tested. So the honest answer to which houses are most at risk is: the ones nobody has tested yet. Look up your county's predicted potential on the radon map, then test.

EPA's Consumer's Guide groups homes by foundation: a basement; a slab-on-grade, which is concrete poured at ground level; or a crawlspace, a shallow unfinished space under the first floor. Many homes combine them, such as a basement under part of the house and a slab or crawlspace under the rest. Foundation type does not decide whether a house has high radon. It shapes where radon gets in and which fix suits the house.

Radon basement levels versus upper floors

CDC says radon levels are often higher in basements and lower levels, and WHO says levels are usually higher in basements, cellars and living spaces in contact with the ground. WHO adds that considerable radon concentrations can also be found above the ground floor, so an upper floor is not automatically low. EPA's advice follows from this: test the lowest lived-in level, and if you start using a lower level, such as a basement, retest on that level.

Radon in slab homes

A slab-on-grade home sits on concrete poured at ground level, in EPA's description, and EPA says homes without basements can have a radon problem too. Cracks in solid floors and construction joints are two of the entry routes EPA lists, and EPA's Consumer's Guide says that in homes with a slab-on-grade foundation, radon is usually reduced by soil suction.

Concrete slab house radon: the most common fix

EPA calls active subslab suction, also known as subslab depressurization, the most common and usually the most reliable radon reduction method. One or more suction pipes go through the slab into the crushed rock or soil beneath, and a fan draws radon from below the home and releases it outdoors. Often only a single suction point is needed.

Crawlspace homes

EPA says covering the earth floor of a crawlspace with a high-density plastic sheet and drawing radon from under it with a vent pipe and fan, called submembrane suction, is the most effective way to reduce radon in crawlspace homes when properly applied. Ventilating a crawlspace can also lower levels in some cases, but may raise energy costs.

WHO lists what decides the radon level in a particular building: the local geology, including the uranium content and permeability of the rocks and soils underneath; the routes available for radon to pass from the soil into the building; radon from building materials; and the rate of exchange between indoor and outdoor air, which depends on construction, the occupants' ventilation habits and how airtight the building is. WHO adds that radon concentrations vary considerably between adjacent buildings, and within a building from day to day and hour to hour.

Area data is still useful background. The radon zone map shows each county's predicted potential, and the state and county radon reports add reported testing data. EPA says its zone map should not be used to determine if individual homes need to be tested, and that no matter where you live, you should test. Some states add their own advice. EPA's state contacts page lists the Minnesota Department of Health's recommendations, summarized below; the Minnesota radon report shows that state's data.

Yes, and the agencies that study it say so calmly. EPA identifies radon as the second leading cause of lung cancer and estimates it is responsible for about 21,000 lung cancer deaths every year in the U.S., about 2,900 of them among people who have never smoked. WHO estimates radon causes between 3% and 14% of lung cancers in a country. EPA also says not everyone exposed to elevated levels will develop lung cancer, and that your chances depend mostly on how much radon is in your home, how much time you spend there, and whether you smoke or have ever smoked.

What are the symptoms of radon in your home?

There are none to notice. Radon has no smell, color or taste, and EPA says the time between exposure and the onset of disease may be many years. CDC says it takes many years for lung cancer to develop, and most people don't have symptoms until lung cancer is advanced. That is why the answer is a test, not a checklist of symptoms. The radon symptoms guide covers what CDC and EPA say about health effects.

Yes, for every home below the third floor. EPA and the Surgeon General recommend testing all homes below the third floor for radon, and EPA's Citizen's Guide says testing is the only way to know if you and your family are at risk from radon. Testing is inexpensive and easy, it adds, and should only take a few minutes of your time. CDC says the same: the only way to know if you have unsafe levels of radon in your home or office is by testing.

That is why Radon411 shows area data as background, never as a verdict: the state and county radon reports show predicted potential and reported tests in other buildings, which can tell you whether a high result would be unusual where you live, but not what your house holds. WHO adds that radon concentrations vary considerably between adjacent buildings, and within a building from day to day and from hour to hour.

Testing is the only way to know the radon level in a specific building. These steps combine EPA's Citizen's Guide and its Home Buyer's and Seller's Guide; the radon testing guide covers devices in more depth.

1. 1

   Pick the level

   Test the lowest level of the home that is, or could be, used regularly, whether it is finished or unfinished.

2. 2

   Pick the room

   A room used regularly, such as a bedroom, family room or den. EPA says not to test in a closet, stairway, hallway or crawl space, or in an enclosed area of high humidity or high air velocity, which may include a kitchen, bathroom, laundry room or furnace room.

3. 3

   Close the house

   For a test of less than four days, close windows and outside doors at least 12 hours before it starts, and keep them closed except for normal entry and exit.

4. 4

   Run it long enough

   EPA says all radon tests should be taken for a minimum of 48 hours. A long-term test, of more than 90 days, better reflects your year-round average.

5. 5

   Place it carefully

   At least 20 inches above the floor, away from drafts, high heat, high humidity and exterior walls, where it will not be disturbed.

Lowest lived-in level

Where EPA says a test belongs: the basement if it is frequently used, otherwise the first floor.

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1. 1Step 1: Take a short-term test.

   • Below 4 pCi/LEven if your test result is below 4 pCi/L, you may want to test again sometime in the future.
   • At or above 4 pCi/LIf your result is at or above 4 pCi/L, take a followup test to be sure.

2. 2Step 2: Follow up with either a long-term test or a second short-term test.

   • Long-term testFor a better understanding of your year-round average radon level, take a long-term test.
   • Second short-term testIf you need results quickly, take a second short-term test. If your first short-term test result is more than twice EPA's 4 pCi/L action level, you should take a second short-term test immediately.

3. 3Step 3: Decide whether to fix your home.

   • After a long-term testFix your home if your long-term test result is 4 pCi/L or more.
   • After a second short-term testConsider fixing your home if the average of your first and second test is at or above 4 pCi/L.

EPA recommends that sellers test before putting a home on the market and fix any problem, and that buyers know the indoor radon level of any home they consider, asking the seller for results or testing if none exist. EPA's myth list says that where radon problems have been fixed, home sales have not been blocked. The buying a house guide covers the transaction.

Can new homes have radon?

Yes. EPA says any home can have a radon problem, new or old. Radon-resistant construction reduces entry: EPA lists a gas-permeable layer under the slab, plastic sheeting, sealing and caulking, a vent pipe to the roof and a junction box for a future fan. Even so, EPA says every new home should be tested after occupancy, and a fan can be added to the passive system if the result calls for it. See radon-resistant new construction.

EPA recommends fixing a home when the radon level is 4 pCi/L or higher. EPA recommends considering a fix when the level is between 2 and 4 pCi/L. CDC adds that reducing radon inside your home will always help reduce your risk of lung cancer, even when the level in your home is less than 4 pCi/L. EPA advises using a contractor trained to fix radon problems, because lowering high levels requires technical knowledge and special skills. Your state radon office can supply names of qualified or state-certified contractors, and the radon professionals directory lists measurement and mitigation providers. The radon mitigation guide explains the systems, and the radon level interpreter helps you read a result. After a fix, test again, and EPA suggests retesting every two years.

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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.

How a fix works, and what it costs, is in radon remediation systems. The short version: EPA's Citizen's Guide says the method primarily used is a vent pipe system and fan, which pulls radon from beneath the house and vents it to the outside, and that most homes can be fixed for about the same cost as other common home repairs.