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She’s thinking of buying a house, but it has a high radon measurement. What should she do?

Someone wrote in with a question:

My Mom, who has health issues, is about to close on a new house in **, NJ. We just saw that ** generally is listed as an area with high radon. If the house has a radon measurement over 4 and the seller puts vents to bring it into compliance, how likely is it that the level will return to 4 shortly thereafter?

Also is 4 a safe amount? I understand that is the EPA guideline while the World Health Organization suggests 2.7. Which level do you consider appropriate?

I forwarded this to my colleague Phil Price (known as “Phil” to you blog readers), who worked for many years as a scientist in the Indoor Environment Department at Lawrence Berkeley National Laboratory. Phil replied:

Unfortunately nobody knows exactly how dangerous it is to live in a house with a radon concentration around 4 pCi/L. Different countries have standards as low as 2 and as high as 10. It’s clear that at levels as high as 12 or 20 pCi/L the residents are at substantially increased risk of lung cancer, but at lower concentrations the danger is not high enough to stick out definitively from the noise, so it’s really hard to know how to extrapolate.

Here are a few facts and observations that might help you decide for yourself, and then I’ll follow up with my personal recommendation which is based on what I [Phil] would do and is not necessarily a recommendation that is good for you or your mom.

Actually, let me start with an answer to your question: if the house has acceptable radon concentrations now (averaged over a full year) then that is unlikely to change spontaneously over time; however, changes to the house or its operation could change things, e.g. if your mom starts heating or cooling parts of the house that have previously been unoccupied. On shorter timescales, the radon concentration is always varying, so a measurement made at one moment

Now, on to those facts I mentioned:
1. The relevant number is the radon concentration in the living areas of the home. That seems obvious, but a lot of measurements are made in unfinished basements or in other areas where people don’t spend much time, such as a crawlspace under the house.
2. Also, the relevant number is the radon concentration averaged over a long period of time — months or years — not the concentration at a given moment.
3. The radon concentration in a basement is normally substantially higher than on the ground floor or above.
4. The indoor radon concentration can vary a lot with time: it might be twice as high in winter as in summer, on average, and it might be four times as high in the highest winter week as it is in the lowest.
5. For most homes, radon mitigation can be performed for under $2500 that will work for many years; you can google “radon sub slab depressurization” to read about this.

Finally, I’ll tell you what I would do. But my choice would not just depend on facts about radon, but also on my personality, so this might not be what your mom should do.

I would buy the house and move in. I would perform a year-long radon test on the lowest level of the home in which I spend time (for instance, the basement if I spent time in a hobby room down there or something, otherwise the ground floor) and after a year I would check the results and hire a radon mitigation company if the result was higher than I thought was safe. I think the 4 pCi/L level is reasonable for making that decision, but if it came back at 3.6 pCi/L or something, maybe I would mitigate even though that is below the ‘action level’.

The idea of waiting that long, knowing that for the whole year you’re being exposed at above the recommended concentration, would freak some people out. If I felt that way, then in addition to the long-term test I might do a short-term test every few months, and if any of the results were really high, I’d hire a mitigation company. But even if the long-term average is fine, the measurement over a short period might be pretty high, so I wouldn’t be too bothered by a single short-term test coming in at 4 or 6 pCi/L, I’d just wait until I had the long-term result. Again, that’s just me. Here is a company that offers various combinations of short- and long-term tests. I have no relationship with them whatsoever, I just looked them up on the internet like anyone could do.

Finally: your mom could consider calling a radon mitigation company and seeing what they say. Most likely they will say they can mitigate just about any house to below 4 pCi/L in the living area; they might even offer a guarantee. Then she could buy the house and go ahead and have a sub-slab depressurization system installed. Odds are pretty good that that would be a waste of a few thousand dollars, but it would give her peace of mind and if it lets her buy a house she likes, it might well be worth it.


  1. James Annan says:

    I would also consider the age of the mother and the plausibility of developing any radon-related health problem within her likely lifespan. Standards may be set in terms of what might be acceptable for a whole life from childhood onwards.

    • Rahul says:

      Exactly what I was thinking. Suppose one is say 70 years old how much is the additional risk of a 4 units radon exposure compared to other risks you face.

      To put it in perspective how’s the risk of say even a 10 unit living space radon exposure to being a smoker?

  2. Matt Skaggs says:

    The EPA currently recommends mitigation:

    Lifetime exposure to 4 pCi/L is associated with a 0.7% chance of alpha particle-induced lung cancer in nonsmokers. James is right that this must be adjusted down substantially for later-in-life exposure.

    While the numbers are high enough to be meaningful, smoking is a lot more dangerous than living in a house with a 4.

    • Dzhaughn says:

      That “association” is probably using measurements of harm from higher levels of exposure combined with a linear model of harm.

      Some think that linear model overstates the risk; I’m inclined to agree, so I don’t worry.

      But, you may disagree. If so, then you think the recommended mitigtaion (from “4” to “2”) only reduces the risk by half: not so great. Can you live with that?

  3. Paul says:

    Mitigation is pretty straight forward. Testing is a lot cheaper too. I don’t do radon, I do some vapor intrusion work. I would test the remediation system so I had a ballpark of what the source concentration was. I would also test areas where my kids spent the most time or where I thought vapors were most likely to come in. Typically areas with lots of utility type slab penetrations.

    A concern for systems is the financial status of the owner. Can they afford to run the system. Can they maintain it. I have seen elaborate systems proposed where the operations costs for the owner was iffy. Because a turned off system is useless.

  4. C. Montgomery says:

    Statistical Modeling, Causal Inference, Social Science, and Radon Exposure Mitigation

  5. Thanatos Savehn says:

    I’d prefer to know the absolute risk. When deciding whether to take the Hardy Toll Road or I-45 to get downtown all it takes to justify the toll is a glance at the carnage statistics for the free road.

  6. Dzhaughn says:

    For an elderly person, radon is a very minor concern compared to proximity to family and friends, or whether one can reasonably function in the house using a walker or a cane. Plan to avoid assisted living as long as possible!

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