Saturday, October 1, 2016
By Jed Williams

Radon Gas, Your Home, and Your Health

Jed Williams
Principal Broker
Hagan Realty
October, 2016

“It’s odorless, tasteless, dissolves instantly in liquid, and is among the more deadly poisons known to man”, alas this time we aren’t talking about a fictitious Australian poison, but rather about Radon gas. Radon is a cancer-causing, radioactive gas. While it may be inconceivable that something you cannot see it, smell, or taste can be harmful, Radon gas exists in unsafe levels in an estimated 1 out of every 5 homes (excluding multi-family) in America and it is the second leading cause of lung cancer in the United States. Despite these facts, very few people are even aware of its existence. Inconceivable.


Radon has seen a bit of recent attention in politics and the press, but it’s far from a new discovery. In fact, it was first discovered back in 1899 at McGill University in Canada by famed English (a Kiwi by birth) physicist Ernest Rutherford. The next year, German physicist Friedrich Ernst Dorn discovered that Radon was the product of the atomic decay of Radium, a byproduct of the natural decay of Uranium.

In 1986 the EPA put out guidance regarding what it considered to be an appropriate “action level” for targeting acceptable and unacceptable levels of Radon gas in American Homes. This guidance persists today and has remained the foundation for a number of current tests, disclosures, and mitigation practices within the real estate industry.

Two years later, the US Congress passed Radon Act 51 which set a target indoor Radon density of 0.4 pCi/L, the same as the EPA had found for the outside air concentration. Unfortunately, two thirds of American homes exceeded this mark and so the EPA’s 1986 guidance has remained the governing number ever since.

In 2009, the World Health Organization published its “Handbook on Indoor Radon: A Public Health Perspective” in which it set a target for indoor levels of just 2.7 pCi/L. The US however has stuck with the EPA’s 4.0 pCi/L number.


Radon is a primary element, like Oxygen or Carbon. It is found on the periodic table with an atomic number of 86, putting it in the noble gas family; the same family as Neon and Argon. Like all noble gasses, it is unreactive and exists as single atom molecules which means it is small enough to pass through most common building materials like drywall, paint, and even concrete block.

Radon density is measured in pCi/L which is read as picocuries per liter. A picocurie is a measure of the radioactive decay of an atom. Essentially, a picocurie per liter is a measure of how many Radon atoms decay into Polonium atoms (atomic number 85) within a liter of air within a 24 hours period. The higher the pCi/L number, the greater the concentration of Radon and the greater the health risk. The EPA’s 1986 guideline was that any home with an average concentration of 4.0 pCi/L or higher should undergo mitigation.

In the outside air, the average Radon density in the US is approximately 0.4 pCi/L or one tenth the EPA’s risk guideline; although there are many areas in the US where the outside air density is closer to 0.75 pCi/L.

Radon is the heaviest known naturally occurring gas. It is 9 times as dense as ambient air, which means it tends to collect in the lowest levels of a given space. Within a home, that typically means the basement.

DC Metro Densities

In the Washington, DC metro area, average Radon gas densities vary tremendously from county to county. In Prince George’s County, MD only 16% of homes measure 4.0 pCi/L or higher while 58% of homes hit that mark in Frederick County, MD. DC, Arlington, and Alexandria all fall below 20% of homes, with Fairfax County having 24% of homes at or over the EPA’s mark.

Basic information on Radon densities by county can be found here.

Health Concerns

According to the US Surgeon General’s office, Radon is the second leading cause of lung cancer with 20,000 cases each year and 14,400 deaths. That equates to approximately one case of Radon related lung cancer for every 15,500 US citizens each year. Smoking, by comparison, causes 7 times more cases, but ironically has a higher survival rate. This is mostly attributed to the fact that, given the public’s lack of awareness of the risks of Radon gas, the chances of detecting lung cancer early in non-smokers is significantly reduced compared to people who smoke.

An individual that lives in a home subject to a 4.0 pCi/L density of Radon gas has approximately a 1 in 100 chance of developing lung cancer over their lifetimes. This is because such a density subjects occupants to approximately 35 times the amount of radiation as the Nuclear Regulatory Commission allows for the fence line surrounding a radioactive waste site.

The relationship between the cancer risk and Radon density is a roughly linear one, meaning reducing the indoor Radon level from 4.0 pCi/L to 2.0 pCi/L will cut the incidence of cancer by just over 50%.

Politics and Law

The EPA arrived at its 4.0 pCi/L action level in 1986 by doing a cost-benefit-analysis for mitigation vs the treatment cost of lung cancer at the time. The calculation found that mitigating homes to the 4.0 pCi/L carried with it a cost of approximately $700,000 (in 1986 dollars) for each lung cancer death it would prevent. In contrast, mitigating to a 2.0 pCi/L level would have meant a cost of nearly $2 million per prevented death. Thus, the guideline was contrived out of a balance of risk vs cost and should not be interpreted as an on-off switch for what level is safe.

In 2016, Montgomery County, MD became the first jurisdiction in the DC metro region to enact a mandatory Radon disclosure law. From October 1, 2016 all single family homes and townhomes, with limited exceptions, sold within the county must either have the seller provide the results of a Radon test or allow the buyer to conduct their own test. There is no requirement for remediation, merely for testing and disclosure.

Radon and Houses

Despite being 9 times more dense than normal air, Radon gets pushed up out of the soil and into a home through windows, walls, exterior joins, and micro-fissures in the foundation itself by diffusive pressures in the ground. The rate at which it comes up out of the ground varies tremendously and can be affected by barometric pressure, temperature, rainfall, and a host of other conditions. It collects inside the home, typically in the lowest points in the house, the basement, and stays there because of its extreme density. This is why Radon is mostly a problem for homes with a subterranean level, but it can affect homes of almost any design. It is exchanged out of the home through windows and doors during the course of normal occupancy and use. This is why vacant homes will often show elevated levels of Radon, because no one is there to open and close the doors and create air exchange between the interior and exterior.

Radon in the Real Estate Contract

While the exact contractual language of the Radon inspection contingencies varies from jurisdiction to jurisdiction, the majority of the forms used in the DC metro area allow for the buyer to perform, at the buyer’s expense, a short-term Radon canister test within a property they intend to buy. In the event that the Radon density is found to be 4.0 pCi/L or greater, the seller is then obligated to install, at the seller’s expense, a Radon mitigation device and have the property re-tested. The language for such Radon tests is an option, and is must therefore be added into a contract in all jurisdictions in the DC metro area.  

Testing and Mitigation

Testing for radon primarily involves the use of carbon capture traps that are placed inside a home for a period typically of 48-96 hours. These test kits are then sent to a laboratory for analysis. Home test kits can be purchased from many local hardware stores such as Home Depot or Lowes. The kits typically cost between $20-50 and the lab test can cost $30-50. Alternatively, there are many third party inspection services licensed to perform Radon test in Maryland, DC, and Virginia.

It is extremely important to note that, because of the variability of Radon gas emissions from the soil due to a host of environmental factors, a single Radon test can often be misleading as to the long term Radon levels in a home. Periodic testing or long term testing can produce more accurate and reliable results.

If elevated levels of Radon are found to exist within a home, there are limited but effective options for mitigation. In most cases, a vent equipped with a low wattage fan is installed that connects to the sump crock or crawl space under a home. The fan creates a very slight vacuum that draws the Radon out from the area and vents it to the exterior of the home. The EPA has found that such methods for mitigation have an estimated 95% success rate to lower the Radon density rate to below 4.0pCi/L and a 70% success rate of lowering the level to below 2.0pCi/L. The cost for mitigation varies but is typically within the range $800-2,500 with $1,200-1,500 being the most common range. While home kits are available, it is highly recommended that a licensed professional perform any mitigation work.

Jed WilliamsJed Williams
Principle Broker and founder of Hagan Realty

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