In researching the subject of Radon mitigation, I came across this article, Titled "Radon - A brief discussion", by Caoimhín P. Connell (Forensic Industrial Hygienist)

Please read that whole article before posting any comments. It's a long read, but I'd like to ensure everyone who comments on this topic has in fact read and understands the article. No biases please! :)

The first paragraph states the following:


A large portion of the general population is under the misconception that the frequently published risks associated with radon are well accepted scientific facts. In reality, the vast majority of well designed studies do not support policy or positions that exposures to indoor radon pose a significant threat to health, and indeed, the majority of those studies indicate that, at concentrations typically seen in homes, as the level of radon increases, the risk of lung cancer goes down, not up.


After reading the science behind Caoimhín's well-written and thorough article, I have to say I agree with his words and message. So what does that mean to an energy auditor? What advice am I to give to a homeowner whose home is under constant depressurization causing backdrafting with their woodstove or failing to pass worst case combustion safety tests, all because of their radon fan in the (nearly-conditioned) crawlspace? I realize as a BPI graduate I am supposed to consider Radon. But what do I tell folks whose Radon mitigation system indicates levels far below 7 picocuries? Should they run that fan that consumes 526 kWh/year, costing them $70/year?

I welcome your input. Love this community!


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There doesn't need to be consensus in the scientific community!!

Facts are facts, findings reflect facts using stated methodologies and goals of the work, not opinions being sorted out.

The issue is risk, risk comes from dealing with low-level radiation poisoning that can be absorbed by skin so you get a skin cancer from radon who would guess that on top of possible lung cancer?

This of course 5 or more years later thus the risk is cancer, if you have a hot isotope next to a cell it's almost certainty one gets a cancer there is no arguing that.

When geographically there is a higher incidence of cancers along with a higher-than-normal radon release in strata than background it demands remediation.

The consensus then must be "reasonable actions" to reduce risk with arguable qualities simple air evacuation is better than not.

This is not complicated, it's adjusting the odds, argue how you will on where to draw the line it's just a legal-code constraint that has some relation to odds and will never satisfy everyone like how much radiation is "legal" now in Japan.

Health risks are high in our cancer-ridden culture, being able to identify the cause of a cancer after the fact is detective work for each case, USGS validates the radon geology, measuring a lot in that area dictates whether it needs remediation or not, health records validated a stab at limits from cancer statistics, it's not going to be perfect ever.

So the realtors have it covered, do it anyway, that's what I see happening so who cares where the line or the science is?

Hello all!

In a recent post regarding radon intrusion, a participant argued that the application of a membrane depressurization system (and fans) installed in the crawlspace would have the added advantage of reducing moisture in the crawlspace (thus reducing mould growth).  In fact, the argument is without support on several levels. 

As I mentioned in another reply, air components generally move from a “source” to a “sink.”  A “source” is an arbitrary point from whence the component comes, and a “sink” is an arbitrary point of termination of movement.  Thus, any two points along a particular path of migration can also be considered to be a “source” or a “sink.” 

Therefore, imagine a little strip-mall containing several businesses.  At one end (Suite #1) is a small T-shirt shop that does silk-screening on T-shirts, and at the extreme other end (Suite #6) other end is small environmental consulting firm that occasionally handles water samples in a small fume hood.  In between the two, is a Real Estate Office (Suite #2), a Dental Office (Suite #3) a Mortgage  Office (Suite #4) and an Insurance Office (Suite #5). 

On some days, when the Consulting Firm operates the fume hood, the pressure differentials are such air moves from Suite #1 through the structure to Suite #6, passing through each successive business from source (T-shirt printers) to sink (fume hood).  On those days, the folks in Suites #4 and #5 complain about a bad odor coming from the Dental Office.   A “certified indoor air quality” guy goes to the facility and (of course) immediately wants to collect “air samples” and he needlessly collects samples using a TO-15 Summa canister and determines that Suites #4 and #5 have “elevated levels of toluene, and ergo, the Dental office (the source) is to blame- problem solved (and of course the fancy laboratory report of the “scientific” samples prove it!)  Here we can see that depending on which compartment one chooses to start, and end their investigation will determine the source and the sinks.  And so it is with residential structures – complex pressure differentials will drive air components from sources to sinks.  

Another type of source/sink will be when a component may have an affinity for the substrate that is different from that of the surrounding air.  For example, at a given relative humidity (%RH), two different materials may have two very distinct values of “water availability.”  Kiln-dried wood removes water which is tightly bound to molecular sites such as hydroxyl groups of polysaccharides, amino groups of proteins, and other polar sites, thus lowering water availability in the kiln-dried wood, and air dried wood does not release that tightly bound water since there is an equilibrium which exists between the water vapor in the air and the movement of water molecules in the substrate called the “water potential” (a complex phenomenon dealing with the entropy of the water molecules that is beyond the scope of this discussion).  At the same (%RH), the two materials will simultaneously act as both sinks, and sources depending on the ambient absolute humidity and temperature- but they will behave differently as those sources and sinks. 

Each material has a specific capacity to sequester a specific volume of water per unit weight of building material, before the water reaches a specific “water availability” value.  This capacity, expressed as weight of water or volume of water is the “hygric buffering capacity” of that material.    For example, let’s look at two building materials – One square foot of aluminum and one square foot of kiln-dried pine – the thickness of both materials is such that the weight of the item is two pounds.  The items are laid flat on a table. 

Now, imagine that one single drop of water (one gram of water) is poured onto both items (that is, the water is going from a source to a sink).  The wood will easily soak up the water but the drop will pool on the aluminum.  We now know that the hygric buffering capacity of the metal plate has been exceeded, but the wood, for all practical purposes remains “dry.”  In fact we find that since the wood “soaks-up” the water, we can continue to pour more and more and more water onto the wood, until the hygric buffering capacity of the wood is exceeded and now the wood has the same “water availability” value as the metal. 

1) Residential crawlspaces have a very significant potential source of water – the earthen floor.

 2) Residential crawlspaces have a very significant potential sink for water – the earthen floor.


That is, if one indiscriminately places a vapor barrier over an earthen floor, one can drive the moisture equilibrium one way or the other way depending on whether the earthen floor for that particular residence is a source (thus decreasing crawlspace moisture) or a sink (thus increasing crawlspace moisture).  All too often, the indiscriminate application of a vapor barrier in a crawlspace ignores the fact that the earthen floor may be the single largest sink for water vapor in that structure! 

We have seen this very problem arise in older homes which for decades never had a moisture problem, until a “certified mold remediator” decided it was a god idea to install a vapor barrier in the dry crawlspace whose earthen floor was exclusively a sink.  The hygric buffering capacity of the crawlspace, as a system, is thus significantly reduced, and in some cases, normal water vapor is now high enough, the hygric buffering capacity of the system is exceeded. 

I have seen where this is dramatically exacerbated when the “certified mould remediator” also decides that it is a good idea to spray encapsulant on all the exposed wood and concrete footer wall in the crawlspace.  The hygric buffering capacity of the system plunges, and now available water values increase, and now, one has a wet crawlspace full of mould in a property that was otherwise just fine.  In several projects, the fix was to remove the vapor barriers, and sand off the encapsulating material and return the crawlspace to an appropriate water equilibrium.  

In fact in several cases I worked on the inappropriate actions of the “certified mould remediators” permitted the growth of Serpula lacrymans and as a direct results of their “mould remediation” actions, we have seen catastrophic structural failure of walls and floors – (resulting in injuries in two structures, when occupants fell through the floors!) 

As I have stated earlier in this thread, before one “fixes” a problem, they really should identify the problem first and determine if the “fix” will actually address the problem.  The application of indiscriminate “fixes” based on nothing more that the myth of argumentum ad populum (i.e. …Well, gosh, everyone else seems to be doing it, so it MUST be a good idea) very often leads to unintended consequences.  And the assumption that putting a vapor barrier in a structure, must necessarily reduce moisture in that structure, is one such example of argumentum ad populum as exhibited by two of the respondents in this thread. 

In the post wherein the proponent of the vapor barrier argument was made, the respondent made five unsupported assumptions:


1) the fungal growth in the crawlspace was significant,

2) the fungal growth in the crawlspace was the result of elevated moisture in the crawlspace,

3) the elevated moisture in the crawlspace came from the earthen floor;

4) the application of a vapor barrier would reduce the elevated moisture in the crawlspace;

5) the vapor barrier would therefore prevent the recurrence of fungi in the crawlspace.


In fact, the opposite of each of these assumptions may be truth, viz

1) There is no indication the presence of the fungal growth was significant.

2) The fungal growth in the crawlspace could have been the result of wet building materials during construction 100 years ago, and the fungus has been dormant ever since.

3) The elevated moisture in the crawlspace could have been the result of off-gassing of water vapor from construction 100 years earlier.

4) The application of a vapor barrier may now result in elevated moisture in the crawlspace;

5) The vapor barrier may now be the cause of a recurrence of fungi in the crawlspace.


This post is already too long, and so, as a separate issue, next week, I will address the reason why the fans may, independent of the vapor barrier, also increase the moisture content in the crawlspace (unless someone wants to steal the thunder and do that for me!)

Cheers!  Have a great weekend, and good health to you!  (And thanks to the off-line comments I have received regarding last week's murder of my patrol partner).


On the humid-wet side of the Cascade Range many homes have wet crawl spaces, some take defense against groundwater levels that rise seasonally.

These are rather difficult to handle and fungi are a symptom, suggest you poll contractors dealing with these problems to ascertain strategies that work for situations that vary greatly.

Also, from my experience the crawl space has a large thermal effect on the entire home, this from building passive-solar homes, they heat up over time and don't cool down as the typical home with a crawl space area for the thermal-mass storage.

So after the third year the crawl space is room temperature, the floor is warm in the morning.

Consider that relating to vapor barriers and random remediation and heating bills in winter most passive-solar have none.

Like Joe Lstiburek says, you can make all the models you want; in the end, the real world scenarios will tell you what really happens in the built environment. How someone can say that crawlspace encapsulation will create problems and not solve them is beyond my understanding. I'm exiting this discussion due to the wrestling a pig in the mud analogy. Pigs love it, I don't. 

Did someone say crawlspace encapsulation will create problems? I must have missed that in this very long conversation. Was it a consensus? My understanding and experience (and that of many on this group) is that it's generally advantageous.

I am with Mr. Connell. Science is a beautiful thing. 

My own experience with Radon mitigation has been the simplistic and unscientific application of Radon mitigation tools, e.g. PVC pipe and an exhaust fan. 

While working for a Mechanical PE we removed the 100 yr old basement floor installing a perimeter drain, vapor barrier, 2" of XPS and radiated the floor. When I contacted the local Radon people I could not get an answer to questions of cfm or negative pressure nor options for other-than-textbook termination of the Radon vent. 

We determined that a passive radon system using the abandoned chimney would be sufficient to reduce the existing 8 piC/L to 4 post vent. 

Since we design residential hydronic radiant heating systems and cooling is only an option in many locals, the lack of a fan blowing around the house mandates the use of controlled ventilation. The properly sized and operated ERV/HRF gives the designer the options necessary to produce positive IAQ in the vast majority of applications and addressing all manner of threats from mold to radon, be they found in new construction or retrofit. 

I have found a quality CO2 monitor the most revealing and accurate of all my air quality tools and have been amazed at house rank a room can get with a couple of humans talking for more than a few hours when the ACH is below 10 cfm. 

Each application is dependent on many physical realities that make the perfect environment beyond the budget of most homeowners, thus the minimum standards for construction. It is when these "minimums" exceed cost-benefit rational that the skeptic must get off the wagon.

Morgan, thanks for that link. A few things I found in that article very much support Caoimhin's point:

The risk of environmental radon levels is not higher now than in the past, when residential exposures were not considered to be a significant health hazard. It has now been raised from a nominal natural background contributor to human exposures to the prime contributor based on a new way of calculating dose, and not on increased exposures in the home due to tighter more energy efficient houses, or new information on radiation dose and/or biologic risk.

No detectable increase in lung cancer frequency is seen in the lowest exposed US miners, i.e. those with exposures <120 wlm, the relevant dose interval for most homes.

Evidence for a health effect from radon exposure is based upon data gathered from epidemiologic studies of miners, and animal studies.

However, no compelling evidence for increased lung cancer risk has yet been demonstrated from "acceptable" levels (<4-8 pci/liter). increased lung cancer risk is primarily in cigarette smokers, and abatement of that risk can best be accomplished by changes in smoking status.

NCRP quotes an uncertainty of +/- 50% in these numbers

I also just recently found a whole lot of information on this subject here. All of his articles support what Caoimhin has been saying about the validity of data to support the EPA's action levels. It's interesting also how the World Health Organization's member countries have also implemented their action levels based on the information our EPA has published (does anybody actually READ the data?) Additionally, I've found many other articles that tear apart the Radon myth here, here, and here. I've just scratched the surface; there are many many more out there...

I posted this topic because I wanted to get to the truth of the matter; to determine if I can safely tell my clients who are in a situation where their Radon mitigation system is causing unsafe backdrafting of their woodstove, that they can turn off that fan and still feel safe against potential lung cancer from Radon exposure. I believe through all of the information given here, coupled with my own personal research, I can indeed tell my clients this.

All of the side topic arguments and opinions aside, there is a compelling amount of evidence that we've been duped about Radon exposure risks. If one really researches this subject of Radon mitigation--looking at the actual data that is cited, following all of the motivations and manipulations behind the EPA's recommended action levels, and of course following the money--one will most likely come to the conclusion that it's a bunch of hype and BS. Can exposure to Radon cause lung cancer? Maybe, but evidence is weak, at best. And when compared to all of the other things in buildings we are exposed to every day that are known for sure to cause cancer (like Benzene and Formaldehyde), Radon is the least of our concerns. In any and all cases though, mechanical ventilation systems seem to alleviate a huge amount of risk to any of these poisons, and that is good enough reason to recommend (and sometimes require) them to our clients. Right?

When a government agency gets so big and powerful that it can make law, science and democracy become our last hope. Having been to more than one EPA sponsored "training" event and been exposed to their propaganda threatening heavy fines and ambulance chasers at the door, I have grown weary of the EPA induced "boogeyman" and insulted by the insidious nature of new "standards" imposed by self-interested bureaucrats. 


More unfunded mandates that states like mine readily incorporate into law without due consideration. The homeowner is clueless and depends on us to sort through fact from fiction. Our rights and responsibilities co-opted by federal bureaucrats with the aid of robotic local officials,

Naturally, it is not their money, so why should they care? If your client is burning solid fuel, at a statistical level, radon is literally the least of their worries. If their radon fan induces a back draft one can hardly argue for radon abatement. Free choice is the key to the proper balance and common sense must be considered even in matters so technical that only people as smart and obviously well-educated as Mr. Connell can fully grasp their full implications.  

the consensus in the scientific community is that radon is bad for human health

I'm sorry anyone grows weary of truth. But the point we're trying to make here is, the consensus is based on bad or incomplete data, and that is highly relevant!

If one thoroughly researches the actual data the policy-makers (not necessarily the scientific community) base their decision-making on, and the fact that MANY scientific studies have shown that it might actually be good for us, and the fact that a banana can have 60 piC/l Radon, and the fact that we are ALL exposed to an average of 2 piC/l all day, every day, and the fact that piC/l is not in any way, shape, or form a valuable measure of alpha particles (the ones that actually modify DNA), and the fact that most other country's policies on Radon are based on the US's policies (the US knows best, right?), one can only come to some conclusions that we might have been mislead on this topic. It should, at the very least, make one go, "hmmmmmm....."
Anybody else going, "hmmmmmmm......"?

Consensus at one time said the earth was flat. Consensus and fact are not necessarily the same thing, no matter how much you "wish" it. 

[Text removed due to non-compliance with Home Energy Pros Guidelines]

In Washington state the consensus is backed up by cancer demographics correlated to geologic strata then a case-by-case basis of risk to exposure.

Radon causes cancers, they are notorious to not be able to trace to the cause, yet, population demographics expose long-term cancer risks, it's how pollution is pinned down as a cause and this was used in this state to establish what reality is here.

From those statistics laws were drawn up to give guidelines on remediation techniques useful to keep emissions below the line-in-the-sand on concentration levels.

Low-level radiation poisoning is found by population demographics, that's relevant and specific data, I have no clue what anyone else is doing, here if a person wants a new build it'll be tested for radon & if a spec-home will get remediation many times when it's not needed to make a sale.

Welcome to the new USA where climate change isn't happening ... socio-pathic inaction the result.

Tom, do you happen to have access to the "cancer demographics correlated to geologic strata" information you're talking about? I can't find that exact nomenclature anywhere on the Interweb. 

As I understand it, data from US counties lung cancer deaths (as shown here)

when compared with a map of Radon concentrations

The two don't convincingly correlate. For instance, in one county on the Olympic Peninsula of Washington, where the Radon concentrations are below 2 pCi/l, that is where the highest mortality rate from lung cancer is for the entire state. This is why I'd like to research your claim more thoroughly. The "science" doesn't back the claim, yet again.

Side note: anyone notice the massive red area in Nevada where all of the atomic testing took/takes place? 


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