What is Radon: Everything You Need to Know to Make Sure Your Home is Safe

Education & Training

What is Radon in a House? The Basics

Radon is an element on the periodic table, a colorless, odorless, and radioactive gas. It comes out of the ground all around the earth and may be accumulating in your home. It can enter homes through gaps in foundations around pipes, wires or pumps. Radon Gas in a house is a common issue. At least one out of every five homes in the US have height radon. It usually gets concentrated most in the lowest level of the home, the first floor (in a slab home), the basement, or a crawl space.

Where Does Radon Gas Come From?

Radon Decay Chain

Radon comes from, oddly enough, Uranium (similar to though not exactly what they make nukes out of). Over billions of years Uranium decays and goes through a series of transformations called the Uranium Decay Chain. More directly, Radon is a decay product of Radium which is widely dispersed in rocks and soil all around the earth.

Most elements in the decay chain are solids and therefore largely stay in the earth where they belong. Radon, however, is a gas and therefore rises through the ground to the surface. When this happens outside it dissipates into the atmosphere and is diluted as much as possible. In contrast, when it rises to the surface under your home much of it will enter your home through cracks and crevices in your foundation or simply through a crawlspace.

Radon (Rn-222) has a half-life of only 3.8 days, but the supply from the ground under your home is stable and consistently renews the levels inside. Radon then decays into other radioactive elements that pose additional danger.

Why Does Radon Come Into My Home?

Radon is a soil gas so it is coming up from and out of the ground. When it comes up under your home it makes its way through cracks and crevices into your home. For most homes the pressure right above the lowest floor in your home is somewhat lower than the pressure just below the slab. So, your house is effectively sucking on the ground pulling soil gasses including radon into your home.

Can I get radon in my home if my home is on a slab or if I have a crawlspace?

The research shows that homes with every foundation type can have high radon. So whether your home is over a basement, on a slab, over a crawlspace, or some combination you may have high radon. Likely the only exception is those neat homes on stilts that you see along some coastlines. The EPA strongly recommends all home types be tested for Radon.

Can I get radon in my new construction home?

Yes you can. Homes of any age may have high radon. Newer homes generally have less cracks and crevices in the foundation but they are also built much tighter so the radon that comes in is not naturally vented out. Your home may have been built according to the new model code Radon Resistant New Construction 2.0. If so, there is a lower chance you may have high radon, but you still may. If your home was built following this code and you still have high radon it will be much easier and cheaper to lower your radon levels than it would be otherwise. The EPA strongly recommends homes of all ages be tested for Radon.

What is the main risk from Radon Exposure?

Over time, exposure to elevated Radon levels increases your chance of getting lung cancer.

How does Radon cause Lung Cancer?

How Radon Causes Lung Cancer

Radon is a radioactive gas. This means it emits radiation. Simply put, these radioactive emissions can damage our DNA. This DNA damage can lead to the onset of cancer.

The odd part about radioactive elements is they actually change what element they are as they emit radiation. This is because they emit protons, neutrons, or electrons as radiation. Because we define elements based on counting these particles the element actually changes.

Radon emits what is called an alpha particle when it decays. Alpha particles are a proton and a neutron and have much higher energy than x-rays. In fact, alpha particles travel at half of the speed of light and each have enough energy to dent bulletproof glass.

Much of the danger from Radon actually comes from what it decays into. Radon decays into solids sometimes called radon daughters. Because radon is a gas and turns into a solid, it forms a very fine radioactive dust. We breath this dust into our lungs. These radon daughters continue to decay and emit radiation directly into our lung tissue.

Our lung cells are particularly sensitive to damage from radiation. This radiation can either pass

harmlessly through our cells, kill the cell it hits, or damage our DNA. It is this damage to our DNA that can lead to lung cancer.

Radon Level Lung Cancer Risk Chart

For non smokers the EPA estimates that:

• at a radon level of 1.3 pCi/l (the average radon level in homes in the US), about 2 out of 1000 will get lung cancer;

• at a radon level of 4 pCi/l, about 7 out of a 1000 will get it; and

• at a radon level of 8 pCi/l, about 15 out of a 1000 will get lung cancer.

While 15 out of 1000 is still thankfully a low percentage, the risk of getting lung cancer for non smokers increases over 700% when exposed long term to radon levels of 8 pCi/l.

The risks are far worse for current or former smokers. If you are a current or former smoker please get your home tested for Radon.

How dangerous is lung cancer caused by radon?

While any cancer is a bad diagnosis, Lung Cancer is the most deadly of the most common cancers. Basically, your chance of surviving lung cancer is low when compared to other common cancers like breast cancer. The five-year survival rate for lung cancer is 56 percent for cases detected when the disease is still localized (within the lungs). However, only 16 percent of lung cancer cases are diagnosed at an early stage. For distant tumors (spread to other organs) the five-year survival rate is only 5 percent.

Sadly, it is estimated that over 21,000 people in just the US die from lung cancer caused by radon exposure every year. That is more than 50 every day.

Radon Compared to Cigarette Smoking

Do I need to test my home for Radon?

Yes you do. The EPA strongly recommends every home be tested for Radon. Importantly,

the only way to know if your health is at risk due to radon in your home is to get a radon test. Even if both of your neighbors have low radon, you may still have high radon in your home. The distribution of Uranium in the soil is non-uniform so the risk is unique to each home site. 

Granted there are regional trends. For instance radon is quite low in Hawaii and generally quite high through much of the west , Midwest, and north east. That said, the EPA, Surgeon General, and the CDC all recommend every home be tested for radon.

What is Radon Testing?

Radon testing is how you find out the radon levels in your home. It is the only way to know if you have high radon. The EPA recommends every home be tested for Radon.

How Can I Test My Home for Radon?

You can either do a radon test yourself with a kit or a consumer grade continuous radon monitor, or you can hire a professional to do a test in your home. If you are in the middle of a real estate transaction you will likely need a professional test rather than a DIY test.

Short Term Radon Tests vs Long Term Radon Test, Which do I need?

Radon tests are divided into either short term tests or long term tests. Short term radon tests range from 48 hours to 89 days. Long term radon tests are 90 days or longer.

Short term radon tests have the advantage of being cheaper and, of course faster. Whereas long term radon tests are more accurate as they can include more variation over time in the test result. A full year long test would give the most accurate result reflecting all seasonal variations in radon levels. Radon levels vary quite a bit hour to hour. This is because the several factors effect the pressure inside your home are dynamic. They include your actions, opening and shutting doors and windows, the wind speed and direction outside, the barometric pressure, precipitation, and the operation of your HVAC system. Short term tests are far more common because 90 days is a long time to wait, and the short term tests are generally quite accurate.

Radon Test with a Radon Test Kit

Radon test kits can either be long term or short term tests. Most people will use a short term radon test kit because they are cheaper and faster. You can buy these at your local hardware store or online such as Amazon. They are quite affordable generally costing only $15-25 per test including laboratory analysis.

Basically you just follow the directions that come with the kit, then mail the kit to the laboratory, and get the results in your email or mail.

The results from a radon test kit are generally very accurate if you follow the directions included in the kit. These are simple and not hard to follow.

Radon Test with a Consumer Radon Monitor

In recent years companies have made radon monitors that are intended for non-professional use in your home. These can be a very good value. They typically cost between $100-250. These are a small electronic device that you put in your home and they monitor and record your radon levels over time (continuously). You can view your levels either on the device screen on or in an app on your phone depending on which one you get. The Corentium Home Model is the most popular and very good. You might wonder what is a radon detector? We a radon detector is the same as a consumer radon monitor.

These devices are similar to the monitors a professional would use doing a test in your home. The main difference is the professional monitors are somewhat more accurate, sophisticated, and must be calibrated annually by a laboratory. That said these monitors are sufficient to monitor your radon levels in your home.

Radon Tests with a Professional Continuous Radon Monitor?

You can hire a local radon professional to come to you home and do a test for you. The pro may use radon test kits, but more often the pro will use a professional grade continuous radon monitor. These devices are very accurate and typically generate detailed reports. These tests will normally be between 2 to 7 days long.

What is a Radon Inspection?

A radon inspection is typically a radon test performed by a radon professional. This could be a home inspector or a radon mitigation pro.

How much do Radon Tests or Radon Inspections Cost?

Radon tests you do yourself should cost $15-30. You can get a consumer radon monitor for between $100 and $200. A test by a radon professional is typically between $75 and $250.

Is One Radon Test Enough or Do I Need More?

The EPA has detailed testing protocols which you can find elsewhere on our site. Basically they recommend if your first radon test comes back high you conduct a second test to confirm the levels. Then make your decision about whether you need to get radon mitigation based on the average of the two.

The EPA has separate protocols for real estate transactions accounting for the shorter time frames. These protocols allow for simultaneous tests with kits rather than back to back confirmation tests. These also allow for relying on a single test with a professional radon monitor.

How often should I to a Radon Test?

The EPA recommends homes be retested for Radon every 2 years or when you make a change to how your home connects to the soil, such as installing a sump pump system. If you get a consumer grade continuous radon monitor you will be able to confirm your radon levels at any time.

How are Radon Levels Measured?

Radon Levels are measured by various techniques between radon test kits and continuous radon monitors. Some methods require a laboratory determine the results. Radon levels are measured in picocuries.

What is a Picocurie?

A picocurie is a measure for the intensity of radioactivity contained in a sample of radioactive material. Because radon is a gas the measurement is a picocurie per liter of air. A picocurie (pCi/l) amounts to 2.2 radioactive emissions per liter of air per minute. These emissions are technically Alpha Particles.

Why are Radon Radioactive Emissions Dangerous?

At first blush 2.2 emissions per minute does not sound like very much. It actually adds up to a surprisingly high number of radioactive emissions per day.

In a typical bedroom (10×10 with 8 foot ceilings) in one day, at a radon level of 4 pCi/l there are:

• Over 287,000,000 radioactive emissions (alpha) per day directly from the decay of radon, and

• Over 574,000,000 beta emissions and another 287,000,000 alpha emissions from the radon daughters.

At a marginally high radon level of 4.0 pCi/l there are over a billion radioactive emissions per day in an average sized bedroom from radon and what radon decays into. Some portion of these decays occur in our lung tissue with is highly vulnerable to damage to radiation.

Radon Cloud Chamber

This is radon in a cloud chamber. You can see the radioactive emissions (alpha particles). This is exactly what happens in our lungs when we breath in radon.

How do my Radon Levels Compare to Other Radiation Sources?

As you might imagine, at that scale, some damage will occur to your DNA when you are living in and breathing that radioactive air. This does not mean you will get lung cancer, but it does mean you have a higher chance.

• The EPA estimates living with radon levels at 4.0 pCi/l is a similar risk to smoking 8 cigarettes every day.

• Living with radon levels of 4.0 pC/l exposes you to the equivalent radiation of getting 200 chest x-rays per year. 

Isn’t Radon Everywhere Including Outside?

Yes radon is everywhere. Here are some statistics to put your radon levels into context:

• Outside the average radon level is around 0.4-0.5 pCi/l.

• The average radon level in homes in the US is 1.3 pCi/l.

• In 23 states the average radon level in homes is above 4.0 pCi/l. (For example in Colorado the average is around 6.5 pCi/l and in Pennsylvania it is 8.6 pCi/l.)

What is the highest radon level?

The highest radon level every measured in a home in the US was in 2014 in Pennsylvania at over 3700 pCi/l!

Doesn’t Everyone Have Radon?

In one sense everyone does. There is a low level of radon even outside. So nearly everyone has some radon in the air in there home. Radon levels vary quite a bit based on where you live. There are maps online that will give you an idea of the average levels in your area. That said, these should not be relied on to determine your radon levels. The EPA recommends everyone get a radon test.

What is a high level of radon?

A high radon level is any level at or above 4.0 pCi/l.

Are my Radon Levels Safe?

Technically there is no safe level of Radon. The EPA treats all radiation risks the same – that is there is no safe level and lower is always better (a linear no threshold risk). That said, the EPA has recommendations for when to take action to reduce your radon levels.

It is important to understand how the recommendations were set. The EPA (and WHO etc.) set their recommendations based on the technology available at the time to reduce radon, the practicality of reducing radon below a certain level, the risks posed by radon, and the overall cost to the economy based on their recommendation. As such, even though the Federal Action Level is 4.0 pCi/l that does not mean that radon levels below that level are safe.

What is the "acceptable" level of radon in air?

Technically there is no “safe” level of Radon in your home. Here is a way to think about it:

  • If your radon levels are at or below 0.5 pCi/l then the air in your home has a similar amount of radon as the air outside. This is very low.
  • If you radon levels are at or below 1.5 pCi/l your radon levels are near the average for homes in the US. This is quite low.
  • If your radon levels are between 2 and 4 pCi/l then the EPA says you should consider taking action to reduce your radon levels. If you are a smoker you should take action to reduce your radon levels. This is a moderate radon level.
  • If your radon levels are at or above 4.0 pCi/l the EPA strongly recommends taking action to reduce your radon levels. This is considered high radon!

Do I need to Fix My Radon Levels? What level of Radon is Dangerous?

Radon Levels Chart

The EPA recommends the following:

• If your radon levels are below 2.0 pCi/l take no action to reduce your radon.

• If they are between 2.0 and 4.0 consider taking action to reduce your radon.

• If they are at or above 4.0 take action to reduce your radon.

For further context, the World Health Organization has set their action level at 2.7 pCi/l.

How do I fix High Radon in My Home?

The good news is that in most homes high radon can be fixed in less than a day of work and for less money than you might think. There are several possible approaches to reducing radon in your home, but by far the most effective and cost effective method is to create suction under the lowest level of your home. This is often referred to sub slab depressurization. These systems can often reduce the radon in your home by more than 90%.

What is the difference between Radon Mitigation, Radon Abatement, and Radon Remediation?

Quite simply there is no difference between Radon Mitigation, Radon Abatement, and Radon Remediation. They all refer to the same job. On this site we refer to this as Radon Mitigation.

What is Sub Slab Depressurization and Why does it Work?

Radon is typically pulled into most homes as a result of lower air pressure inside the house than outside. This pressure difference is usually caused by environmental factors such as wind or temperature and the operation of household appliances (especially your furnace). This means your house is basically sucking on the soil all the time, actively pulling radon into your home.

Radon Mitigation via sub slab depressurization works by creating suction under the lowest level of your home. This makes the space below your slab lower pressure than your home. When this happens air molecules are less likely to move from below the slab into your home.

How does Radon Mitigation Work if I have a Basement?

The primary approach to radon mitigation is sub slab depressurization. This means reducing the pressure under the part of your home in contact with the ground. So, in a home with a basement this means creating suction under your basement floor/slab. So there will be a PVC pipe connecting to your slab in your basement hopefully in an unfinished space. Then a radon mitigation fan will be installed either outside your home or in the attic to create the suction.

How does Radon Mitigation Work if my home is on a slab?

For homes on a slab radon mitigation works the same way it does for those with a basement. The primary difference being that the connection to the slab must happen on the first floor of the home. As there is typically less unfinished space in a slab home than in a basement it can be a challenge to find a suitable location for this connection.

How does Radon Mitigation Work if I have a crawlspace?

Some homes have a space underneath, smaller than a basement and with a dirt floor. In such a crawlspace there is no slab to create suction underneath.

To mitigate radon coming in through a crawlspace the installer must seal up the crawlspace floor with durable plastic that is sealed to the walls and supports. Suction is then created on this plastic covering. This type of mitigation works well but does take longer to install and costs more than other types of installs.

How does having a sump pump system effect my Radon Mitigation System?

For homes with a sump pit and pipe system underneath the sump system typically helps make the system far more effective as the suction from the radon mitigation system can easily extend throughout the sump system.

In many cases with a sump pit, the pit itself is a good place to create the suction on the slab. Local regulations differ on this but it is an effective way to create suction on your slab. In this instance no holes are drilled through the slab and the sump pit itself is used.

How does Radon Mitigation Work if I have more than one type of foundation under my home?

If your home has more than one foundation type, such as a basement and a slab, or a basement and a crawlspace, then the goal will be to install one radon mitigation system engineered so that the one fan can create the needed suction to each foundation type. This can be a design and engineering challenge and is one situation where a real radon mitigation professional who can design the optimal system for your home.

Where does the Radon System Get Installed in my Home?

Every house is different. That said, there are two primary ways to route a radon mitigation system.

In the most common installation the suction pipe goes from the suction point(s) below your home to the outside where the fan is mounted on the side or back of your home. The pipe then extends up the wall to your roof line to discharge the radon safely into the atmosphere. This is a standard exterior installation and the most affordable option.

In some homes it is possible to route the suction pipe from the lowest level of your home vertically through the house (often garage), and install the fan in your attic. The discharge pipe then exits through your roof like a plumbing vent.

This is more of an aesthetic difference than a functional one. Both types of installs work well and last a long time.

What is a Suction Point, and How Many Suction Points do I need?

Radon Mitigation System

A suction point is a place where your radon mitigation system connects with your foundation to create suction. You may need more than one. This is determined by several factors:

• The foundation type(s) under your home,

• The number of foundation types under your home,

• Whether or not you have a sump system installed,

• The size of your home,

• Your radon levels, and

• How permeable the material below your slab is.

Most homes built in the last 20 years have relatively modest sized slabs, permeable sub slab material, and sump systems installed. For these homes one suction point is typically enough. You might need more than one suction point if you have one or more of these:

• a very large home,

• very high radon,

• an older home, or

• multiple foundation types under your home (a basement and a crawlspace for instance).

Your Radon Mitigation Pro will determine whether you need more than one suction point as a part of their design of your Radon Mitigation System.

What is a passive radon mitigation system?

A passive radon mitigation system is installed in a new construction home as it is being built. Homes build following the Radon Resistant New Construction 2.0 model code will have a passive radon mitigation system installed. In some cases a passive radon mitigation system may be enough to reduce the radon to the desired level. Even if not sufficient by themselves, these systems are easy and cheap to upgrade to an active radon mitigation system.

How much does a Radon Mitigation System Cost?

Radon mitigation systems typically cost between $800 and $2500. Your cost will depend on the prevailing prices in your area and the complexity of the system you need. Many newer homes are relatively simple installs. If you have a crawlspace it will be on the more expensive end.

How long does it take to install a Radon Mitigation System?

Most radon mitigation systems can be installed in one day. If you have a more complex or difficult system to install it may take 2-3 days to complete.

What Qualifications do Radon Mitigation Pros have to have?

Being a Radon Pro is a specialty trade and relates to making your home safe. Unlike something like being a handyman or building a fence, the qualifications and knowledge of your radon pro are a big deal.

States have different requirements for a radon pro to be qualified to fix high radon. Some require licensure, some certifications, and some stated are simply unregulated. Your radon pro may take the additional step to become nationally certified.

The state standards are a good place to start but may not be comprehensive and in an unregulated state not even exist. You still need to do the work to ensure your pro is qualified.

How should I choose a Radon Mitigation Pro?

Fundamentally hiring a radon pro is like hiring any other specialty contractor. You should always get multiple quotes, confirm experience, confirm qualifications, ask about guarantees, and ask about insurance.

Radon Mitigation Pros differ quite a bit in how they assure you of the quality of their work. Assuming a radon pro is qualified to do the work you should then consider several other things:

• Did they come out an in person to give you a quote?

• Did they give you a written estimate?

• Do they use a contract setting out exactly what they are promising?

• Do they offer a performance guarantee?

• Do they offer system warranties?

We have also put together a free detailed checklist for you to use in vetting your radon pros. You can use it to make sure you have at least thought of the type of questions you might want to ask. Check it out here: How to Hire a Radon Mitigation Pro Checklist.

Author: John Mattox - Home Inspector & Radon Pro


Comments (6)

John Pusa
Berkshire Hathaway Home Services Crest - Glendale, CA
Your All Time Realtor With Exceptional Service

Welcome to the ActiveRain community. Congratulations on your first post.

Aug 28, 2021 05:09 PM
John Pusa
Berkshire Hathaway Home Services Crest - Glendale, CA
Your All Time Realtor With Exceptional Service

Hello John Mattox very good helpful report for everything to know about radon to make sure a home is safe.

Aug 28, 2021 05:11 PM
Margaret Rome Baltimore 410-530-2400
HomeRome Realty 410-530-2400 - Pikesville, MD
Sell Your Home With Margaret Rome

John Mattox 

WOW, a radon level of 3700 pCi/l! Was the remediation successful?

And I thought my listing with 146 was high!

Aug 28, 2021 07:46 PM
Will Hamm
Hamm Homes - Aurora, CO
"Where There's a Will, There's a Way!"

Hello John, and Welcome to the Rain where we all learn from each other and help each other.  Great blog.


Aug 29, 2021 06:18 AM
Joan Cox
House to Home, Inc. - Denver Real Estate - 720-231-6373 - Denver, CO
Denver Real Estate - Selling One Home at a Time

John, I suggest a radon test with every buyer, most do one, some don't.   The highest I have ever seen was 29.

Aug 29, 2021 01:10 PM
George Souto
George Souto NMLS #65149 FHA, CHFA, VA Mortgages - Middletown, CT
Your Connecticut Mortgage Expert

John Mattox welcome to ActiveRain, and congratulations on successfully posting your first blog on this site.

Sep 09, 2021 02:28 PM