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False Positive Radon Tests: 4 Things Listing Agents Should Be Aware Of

Radon is a radioactive gas that is said to be the leading underlining cause of lung cancer in the U.S.A. Radon is a gas that is naturally occurring that is formed from uranium breakdown with the water, rocks and soils around and below the structure. Typically, when purchasing as home a home inspection company will perform a radon test. Routine radon tests should be performed as the initial radon test performed by your local home inspector will only give you an idea of the radon levels at the time of the home inspection. Radon readings over 4.0 pCi/L are considered high, and a radon mitigation system will be recommended by your local home inspection company.

What happens if the radon results return at 4.1 pCi/L (.1 over)?

The home inspection company performing the home inspection will usually test over a 48-hour period. If a radon test returns slightly high results you may want to consider some external factors that are not typically present and request a retest of the radon levels. Various factors the seller and home inspection company should consider when performing radon testing:

High Winds


Precipitation Home Construction

If the factors are not accounted for the home inspection company may not be able to fully consider a false positive and in some scenarios a false, negative. Home inspectors must account for all the variables that may skew the radon testing results.


High winds, especially extremely high winds can affect the radon levels in your home in a couple of ways. The wind may increase or even decrease the radon levels in your home leading to an inaccurate radon reading.

If the outside winds hit your home on the side of the structure with the most openings such as windows or doors the wind will cause POSITIVE indoor pressure. Positive indoor pressure is when the outside air is ENTERING the home at a faster rate than the air leaving the home. Positive air pressure leads to radon gas exiting the home as the outside air entering the home is pushing the gases out.

The 1st diagram on the very left reflects air entering the home - while pushing the interior air out.

The middle diagram reflects Negative air pressure which is the majority of the air leaving the home.

On the flip side when high winds hit the structure that do not contain a lot of openings such as windows and or doors, this will lead to more air leaving the structure than entering. The pressure in the home is now considered negative and the outside air especially under the soil will be pushed into the structure. The radon gas from the soil will enter the basement at a higher-than-normal rate. As more radon enters the house the radon test is temporarily skewed to reflect a higher than normal radon readings. A reputable home inspection company should take into consideration the wind conditions and recommend a re-test if the results are slightly over normal levels.


During the colder winter months the radon levels may be higher than normal and peak during extremely cold months. When the needle drops during the cold months; all of the windows within the structure are closed.

As the weather warms up and the sun is shining, windows are open, and the fresh air helps with ventilation and air circulation. The home inspector should take into consideration the air tightness of the structure. Although an elevated radon reading should not be excused a second test may be recommended if the home was closed up for a few weeks, vacant and the radon results were .1 or .2 over. The home inspection company should take all factors into consideration when advising the buyer or seller.


Precipitation can increase radon levels due to occupants' reaction and associated weather conditions that accompany precipitation.

Heavy rains may cause the occupants to close windows and doors just like when the outside temperature drops. Heavy rains also sometimes bring high winds. As previously stated above the high winds, depending on the side of the structure they are hitting may increase or decrease radon levels.

The EPA released a statement that “snow, sleet and rain” can push the radon gas back toward the soil. The soils overall radon levels can increase which may lead to more radon gas entering your home.

Home Construction

The way the home is built can play a big factor on the radon levels. Older homes tend to allow more air to pass through creating natural air circulation. New homes are built to meet the new energy code ratings. The energy code requires different preventive measure of air leakage around windows and doors and other components of the home. In a nutshell the home is tightly buttoned up preventing air movement from entering or exiting the home. Newer construction homes tend to have higher radon levels.

Older homes can have elevated radon levels also, but this depends on the location and how the structure is built. Typically speaking the structure was not built-in accordance to current energy regulations and therefore can allow for natural air circulation.

In conclusion, radon levels can vary. The location of the structure is the strongest factor determining radon levels. Radon levels should not be excused but they should be contested if they are slightly over the 4.0 pCi/L threshold. The factors stated above should be especially considered when the radon results are slightly off.

Shield Guard Home Inspections performs radon testing in Albany, Colonie, Schenectady, Troy, Hudon, Saratoga, Averill Park and the entire Capital District.

(518) 649-9111

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