Rain and Radon Levels

Rain and Radon Levels in your Home

Spring weather has brought unrelenting rain to Kansas City this year, causing widespread flooding and damage to homes. The effects of rain can be felt in many areas of our lives, including the impact on radon levels in our homes. We want to take some time to educate our community about how exactly rain and radon are related.

Understanding Constant Outdoor Radon Levels vs. Indoor Radon Levels.

Firstly, we want to be clear that rain does NOT CAUSE radon. Every home/structure has radon. In general, radon in outdoor air does not represent a significant health risk to the general population.

In general, radon in outdoor air does not represent a significant health risk to the general population. Radon concentrations are higher indoors and in areas with minimal ventilation.

Rain & Radon Chart: Outdoor vs. Indoor Radon Concentrations Rain
Rain & Radon Chart: Outdoor vs. Indoor Radon Concentrations Rain

How are Radon Levels Calculated?

Radon concentration in air is measured as (Bq m−3). Typical outdoor radon concentration ranges between 1 and 100 Bq m−3.

Outdoor / Indoor Radon Ranges

Outdoor Radon Level Range (1 and 100 Bq m−3 )  vs. Indoor Radon Level Range (5 Bq/m3 to 70 Bq/m3)

Outdoor / Indoor Radon Averages

Outdoor Radon Level Average (5 Bq/m3 to 15 Bq/m3)  vs. Indoor Radon Level Average (40 Bq m−3)

EPA Radon Action Level

In the United States, the EPA has set the action level for radon at 4.0 pc/l. The World Health Organization (WHO) recommends an action level of 2.7 pc/l.  For more details on general radon facts, look here.

It is estimated that people spend 20% of their time outdoors, resulting in the average person spending the other 80% indoors. 80% of the time, we are exposed to radon levels that exceed the EPA’s radon action level of 4.0 pc/l.

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8775861/

So, How Does Rain Affect Radon Levels?

The explanation involves a variety of different factors. There have been multiple studies conducted that have measured how the weather directly influences radon levels (or concentrations). Numerous factors can influence radon flux from soil and, consequently, outdoor radon concentration. Rainfall and snowfall decrease radon flux.

An increase in atmospheric pressure, rainfall, and snowfall decrease the radon flux, while increasing wind speed or temperature increases it.

AlphaEnergy Laboratories has concluded,

“Rain/storms – Storms systems bring lower pressure air around your home. This lower pressure causes radon to “flow” from the soil to the air faster than normal. If there is heavy rainfall and the ground becomes saturated with water, it is harder for radon to find a path through the soil outside the home. This increase in pressure below the surface can increase the radon entering your home – your home has now become the easiest path for radon to reach the air! Radon’s normal “escape routes” can become blocked, creating heavier pressure on the soil and pushing the radon gas into lower pressure areas like your home, school, or business. Conversely, rainfall could open up some new “routes” for the radon to move easier through, decreasing your levels.”

This is how it works.

Think about how you would concentrate any blast of air or water using a tool or attachment to explain better. You would narrow the exit space and increase pressure.

Radon is an inert gas, meaning it is always in search of the path of least resistance.   With rain comes pressure changes in the atmosphere and increased density in the soil, thus creating an obstruction in the otherwise passive passage of natural gasses like radon. In other words, the gas has to go somewhere, and the atmospheric changes create more pressure and less room to do so.

While wet soil may prove an obstacle for radon; an unsealed sump pump, or even just a crack or hole in your foundation, is an unwarranted invitation for radon in your home. Increased soil moisture (especially in spring following snowmelt) increases radon concentration by 10-20%.

It is important to note that the moisture effect on radon levels is not just speculation, as it has been studied for years. Of those studies, the major conclusion is:

Fact: Partitioning of radon gas between the water and air fractions of soil pores is the main factor increasing soil air radon concentration with the increasing water saturation factor.”

 What about humidity?

Fact: “At a constant value of radon concentration, measured values have been found to increase linearly with increasing humidity, from 30% RH up to a value of ∼85% RH”

Rain & Radon Chart: Kansas City Monthly Average Humidity
Rain & Radon Chart: Kansas City Monthly Average Humidity

Should I Only Do Radon Testing in my House When it’s NOT Raining?

US Annual Average Rainfall in Inches
Rain & Radon Chart: US Annual Average Rainfall in Inches

Fact: Throughout the year, there are 90.8 rainfall days, and 39.06″ (992.2mm) of precipitation is accumulated.

On average, 25% of an entire calendar is how much rain falls. While it is true that rain will increase the average radon concentration in your home during that time, it doesn’t change the fact that radon does exist in your home 365 days of the year.

During times of rain, we are spending that time indoors and are being exposed to higher than average levels of radon.

We want your home to be safe regardless of the weather conditions outside. When it’s raining, we are more likely to be spending time inside our homes. We can look at rainy days as mother natures subtle nudge to make you more aware and consequently, more in control of the radon levels in your home 365 days a year.

Testing is the only way to find out your home’s radon levels, there really is no perfect time to test other than NOW.

Rain & Radon Chart: Kansas City 1991-2020 Precipitation Average
Rain & Radon Chart: Kansas City 1991-2020 Precipitation Average

What Can I Do to Prevent Radon Levels Above the EPA’s Action Level?

The first step is to be PROACTIVE.

Make sure your home is safe today by calling Certified Radon at 816.587.3500 or, click here to request a free estimate to have an industry-certified professional test the radon levels in your home.

We can’t stop the rain, but Certified Radon can stop radon from making itself at home!



Link to World Health Organization handbook: