Health Risk or Hype? Questions and Answers About Radon

A portion of this article is an excerpt from Building Radon Out, a Step-by-Step Guide on How to Build Radon-Resistant Homes, published by the U.S. Environmental Protection Agency Office of Clean Air (published November 2004).

Radon is a radioactive gas. It comes primarily from natural deposits of uranium and radium in soils, which can be found everywhere in the world. Uranium is present in rocks such as granite, shale, phosphate and pitchblende. Uranium breaks down to radium, which then decays into radon. This gas can easily move up through the soil into the atmosphere.

Radon is in the soil and air everywhere in varying amounts. People cannot see, taste, feel or smell radon. There is no way to sense the presence of radon. Radon levels are commonly expressed in picocuries per liter of air (pCi/L), where a picocurie is a measure of radioactivity. The national average of indoor radon levels in homes is about 1.3 pCi/L. Radon levels outdoors, where radon is diluted, average about 0.4 pCi/L.

Radon in the soil can be drawn into a building and can accumulate to high levels. Every building or home has the potential for elevated levels of radon, even those built with radon-resistant features.  The EPA recommends taking action to reduce indoor radon levels when levels are 4 pCi/L or higher.

Is radon a significant health risk?

When radon enters a home, it decays into radioactive particles that have a static charge, which attracts them to particles in the air. These particles can get trapped in your lungs when you breathe. As the radioactive particles break down further, they release bursts of energy, which can damage the DNA in lung tissue. In some cases, if the lung tissue does not repair the DNA correctly, the damage can lead to lung cancer.

Not everyone exposed to elevated levels of radon will develop lung cancer, but your risk of getting radon-induced lung cancer increases as your exposure to radon increases (either because the radon levels are higher or you are present in the home longer). Smokers who have high radon levels in their homes are at especially high risk for getting radon-induced lung cancer.

The following lists organizations that state radon is a health threat in homes:

-U.S. Surgeon General

-American Medical Association

-American Lung Association

-Centers for Disease Control

-National Cancer Institute

-National Academy of Sciences

-Environmental Protection Agency

How does radon enter a home?

Four main factors drive radon entry into homes. All of these factors exist in most homes throughout the country.

1. Uranium is present in the soil nearly everywhere in the United States.
2. The soil is permeable enough to allow radon to migrate into the home through the slab, basement or crawlspace.
3. There are pathways for the radon to enter the basement, such as small holes, cracks, plumbing penetrations or sumps. All homes have radon entry pathways.
4. An air pressure difference between the basement or crawlspace and the surrounding soil draws radon into the home.

Is there a safe level of radon?

There is no known safe level of radon. As your exposure to radon is increased, so is your risk for developing lung cancer. Even radon levels below 4 pCi/L pose some risk.

How does air pressure affect radon entry?

The air pressure in a house is generally lower than in the surrounding air and soil, particularly in the basement and foundation levels. This difference in pressure causes a house to act like a vacuum, drawing air containing radon and other soil gases in through foundation cracks and other openings. Some of the replacement air comes from the underlying soil and can contain radon.

One reason why this pressure difference occurs is because exhaust fans remove air from inside the house. When this air is exhausted, outside air enters the house to replace it. Another cause for a pressure difference is that warm air rises and will leak from openings in the upper portion of the house when temperatures are higher indoors than outdoors. This condition, known as "stack effect," causes unconditioned replacement air to enter the lower portion of the house.

Mechanical systems, such as the furnaces or central air conditioners, may also contribute to the difference in air pressure. In areas with very short mild winters, mechanical systems can be the dominant driving force. Air handlers and leaky return ducts can not only draw in radon, they can also distribute it throughout a home.

What can you do to reduce radon in new homes?

You can easily draw radon away and help prevent radon from entering the home with the following steps:

Install a sub-slab (or sub-membrane) depressurization system
The objective of these systems is to create a vacuum beneath the foundation which is greater in strength than the vacuum applied to the soil by the house itself. The soil gases that are collected beneath the home are piped to a safe location to be vented directly outside.

Use mechanical barriers to soil gas entry
Plastic sheeting and foundation sealing and caulking can serve as barriers to radon entry, entry of other soil gases and moisture.

Reduce stack effect
Sealing and caulking reduce stack effect, and thus reduce the negative pressure in lower levels in the home.

Install air distribution systems so that soil air is not "mined"
Air-handling units and all ducts in basements and, especially, in crawlspaces should be sealed to prevent air, and radon, from being drawn into the system. Seamless ducts are preferred for runs through crawlspaces or beneath slabs. Any seams or joints in ducts should be sealed.

Does foundation type affect radon entry?

No, because radon can literally be sucked into a home, any home can potentially have a radon problem. All conventional house construction types have been found to have radon levels exceeding the action level of 4 pCi/L.

Basement
Radon can enter through floor-to-wall joints and control joints and cracks in the slab.

Slab-On-Grade
Radon can enter a  home regardless of whether or not there is a basement. Slabs built on grade can have just as many openings to allow radon to enter as do basements.

Crawlspace
The vacuums that exist within a home are exerted on the crawlspaces causing radon and other gases to enter the home from the earthen area below. Even with crawlspace vents, a slight vacuum is still exerted on the crawlspace. Measurements in homes with crawlspaces have shown elevated radon levels.  

Manufactured Homes
Unless these buildings are set up on piers without any skirting placed around them, interior vacuums can cause radon to enter these types of homes as well.

Can we keep radon out by sealing the cracks?

Sealing large cracks and openings is important to do when you build a home, both in the lower portion of the home to reduce radon entry points, and in the upper portion of the home to reduce stack effect. However, field research has shown that attempting to seal all of the openings in a foundation is both impractical and ineffective as a stand-alone technique. Radon can enter through very small cracks and openings. These small cracks and openings are too small to locate and effectively seal. Even if all cracks could be sealed during construction, which would be costly, building settlement may cause new cracks to occur. Therefore, sealing large cracks and openings is one of the key components of radon-resistant construction, but not the only technique that should be employed.

What are the radon-resistant features?

The techniques may vary for different foundations and site requirements, but the basic elements of the passive sub-slab depressurization system are as follows:

Gas-permeable layer
Usually a 4-inch layer of clean, coarse gravel is used beneath the slab to allow the soil gas to move freely underneath the house. Other options are to install a loop of perforated pipe or soil gas collection mat (also known as drainage mat or soil gas matting).

Plastic sheeting
Polyethylene sheeting is placed on top of the gas permeable layer to help prevent the soil gas from entering the home. The sheeting also keeps concrete from clogging the gas-permeable layer when the slab is poured.

Vent pipe
A 3- or 4-inch (recommended) PVC or other gas-tight pipe (commonly used for plumbing) runs from the gas-permeable layer through the house and roof to safely vent radon and other soil gases above the house. Although some builders have used 3-inch pipe, field results have indicated that passive systems tend to function better with 4-inch pipe.

Junction box
An electrical junction box is wired in case an electrical venting fan is needed later to activate the system.

Sealing and caulking
All openings in the concrete foundation floor are sealed to prevent soil gas from entering the home. Also, sealing and caulking the rest of the building envelope reduces stack effect in the home.

In many parts of the country, the gravel beneath the slab (gas-permeable layer), plastic sheeting and sealing and caulking are already employed for moisture reduction. In these cases, simply adding the vent pipe and junction box is extremely cost-effective for reducing radon, and so cost-effective that even a cost-conscious builder like Habitat for Humanity has been adding these features in many of its homes.

What pulls the soil gas through the pipe?
If the pipe is routed through warm space (such as an interior wall or the furnace flue chase, following local fire codes), a natural draft is created in the pipe due to the stack effect. Because this method requires no mechanical devices, it is called a passive soil depressurization system.

If further reduction is necessary to bring radon levels in a home below the action level of 4 pCi/L or even lower, an in-line fan can be installed in the pipe to activate the system. The system is then called an active soil depressurization system.

Is there a way to test the lot before building?

Soil testing for radon is not recommended for determining whether a house should be built radon-resistant. Although soil testing can be done, it cannot rule out the possibility that radon could be a problem in the house you build on that lot. Even if soil testing reveals low levels of radon gas in the soil, the amount of radon that may enter the finished house cannot be accurately predicted because one cannot predict the impact that the site preparation will have on introducing new radon pathways or the extent to which a vacuum will be produced by the house.

Why not wait to install the features until after the home is completed and a radon test is performed?

It is much easier and far less costly to prepare the sub-grade to improve gas flow before the slab is cast. Also, the pipe itself can be run more easily through the house before it is finished. This significantly improves aesthetics and can reduce subsequent system operating costs by planning to route the pipe through warm space to maximize passive operation of the system.

EPA recommends that all homes built in Zone 1 (high radon potential) areas have radon reduction systems. Refer to zone map found athttp://www.epa.gov/radon/zonemap.html . If you are building in a Zone 2 or 3 area, the homes you build could still have high radon levels, particularly if there is a radon "hot spot" in your county. According to an annual survey by the NAHB Research Center, about 60,000 homes in Zone 2 and 3 are built with radon-resistant techniques each year. Contact your state radon office for more information.

What can you do to reduce radon in existing homes?

If high concentrations of radon are found in an existing home, there are still options. Improving the ventilation in an area is often sufficient to solve the problem. In other cases, it may be necessary to limit the amount of radon getting into the home by sealing or otherwise obstructing the access points. A professional should be engaged to ensure that the radon is effectively blocked. Typical radon mitigation systems can cost between $800 and $2500, according to the EPA.

Testing For Radon

Testing for radon can be accomplished in one of several ways. Charcoal canisters, alpha-track detectors and charcoal liquid scintillation devices are exposed to the air in your home for a specific amount of time and then sent to a lab for analysis. Do-it-yourself kits that are available from a number of outlets measure radon in this manner. Devices are placed in the lowest structural level of the home’s livable space, often the basement, at least 20 inches from the floor. The device must be left undisturbed in an open area, away from air drafts, exterior walls and direct sunlight.

Unlike these devices which take only a single measurement, continuous radon monitors or CRMs take multiple measurements, every hour for 48 hours, to provide more reliable results.  CRM devices have tamper-proof features that indicate if the power has been turned off or if the monitor has been moved.  They also measure humidity and temperature to alert you if the testing environment was altered, thus possibly rendering the results of the test inaccurate. Professional radon inspectors (many of whom are home inspectors) are formally trained to properly use the testing equipment and analyze the results.

Homebuyers Beware

If you’re buying or selling a home, radon can be a significant issue. Buyers should be aware of the radon risk in their area and determine whether a radon test is desirable. When in doubt, the EPA always recommends testing. The cost of the test (as well as a mitigation system if needed) can be built into the house price. If test results already exist, make sure they are recent or that the home has not been significantly renovated since the test was performed. If in doubt, get a new test done. If you’re selling a home, having a recent radon test is a great idea. By being proactive, you can assure potential buyers that there is no risk and avoid the issue from the start.

Radon is a reality. But it is a reality that we can live with. Proper testing and mitigation, can eliminate radon as a health threat. For more information, visit the EPA web site on radon at http://www.epa.gov/radon.