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Musings of an Energy Nerd

All About Radon

If you are worried about radon, the first step is to test your indoor air

Before pouring a basement slab, remember to install the radon vent pipe. The photo shows workers installing perforated plastic pipe on the interior side of the footings. [Photo credit: New Hudson Valley Passivhaus - www.newhudsonvalley.com]
Image Credit: www.newhudsonvalley.com

Several colorless, odorless gases can injure your health. For example, carbon monoxide can kill you in minutes. Radon takes longer — usually decades — to kill you, and (fortunately) death is less certain.

People who have lived for many years in a house with elevated levels of radon gas have a higher than average chance of getting lung cancer. Because of this risk, the U.S. Environmental Protection Agency (EPA) advises homeowners to test the air in their homes for the presence of radon. If testing reveals radon at levels above 4 picocuries per liter, you should probably arrange for a contractor to install a radon mitigation system in your house.

Radon is a naturally occurring radioactive gas that is present in outdoor and indoor air. Radon is produced by the natural decay of uranium, an element that is present in nearly all soils. Because of the stack effect, the lower layer of indoor air in most homes is at a negative pressure with respect to the outdoors, especially during the winter. This negative pressure draws soil gases into the home through cracks in the foundation: for example, through cracks between a basement slab and the foundation walls, through control joints in the slab, through cracks around water pipes that penetrate the foundation, and through sump pits. About 1 in 15 U.S. homes has a high level of indoor radon.

It’s difficult to predict the radon levels in an untested home. High radon levels are possible in new homes as well as old homes, and in tightly sealed homes as well as leaky homes. According to GBA technical director Peter Yost, the following factors affect a home’s radon levels: the radon concentration in the soil under the house; the moisture content of the soil (dry soil allows radon to move more freely than damp…

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35 Comments

  1. John Nicholas | | #1

    Active System New Construction
    Martin,

    I understand center of home for passive systems. What about an active system in new construction? I have builders and contractors installing the riser in the Mechanical Room. Slab on Grade Construction. Is this acceptable? Is it wise?

    Should we use another center of home location? Is an edge of the home location, within the envelope and fan in the attic OK! I'm thinking a boxed in chase in the rear corner of a closet.

  2. User avater GBA Editor
    Martin Holladay | | #2

    Response to John Nicholas
    John,
    It's rare to install an active radon mitigation system during new construction. After all, you can't test the home until construction is complete -- so why install an active system now, when such a system may be unnecessary?

    To answer your questions:

    1. The vent pipe of an active system does not need to be located in a warm section of the house. Since the fan will pull air through the pipe, the stack effect is irrelevant. Many vent pipes for active systems are installed outdoors, attached to the siding.

    2. It's best if the vent pipe of a passive system is in a warm location. If the house has a good thermal envelope -- in other words, a good air barrier and plenty of wall insulation -- then it's fine to locate the vent pipe in the corner of a closet. Just make sure that the exterior walls of the closet are well insulated, and that there are no air leaks in the vicinity.

  3. Bert Matter | | #3

    another look at radon
    http://www.lewrockwell.com/2003/11/bill-sardi/the-radon-fraud/

    Here is an interesting article by medical journalist Bill Sardi. The radon fraud. From this article ,the evidence for harm from radon seems pretty weak.

  4. Kevin Dickson, MSME | | #4

    Cold slab problems?
    "If you pay 12.5¢ per kWh for electricity, the cost to operate a radon fan will range from about $22 to $110 per year."

    If you heat and use your basement, the extra cooling of your slab will have an even higher effect on your heat usage. In most cases, the air moving in the slab is the same as the ground temperature, which is constant through the year. In newer construction, the slab may be insulated, so there would be no effect.

    Some systems tie the radon system to the exterior footing drain. If the footing drain is daylighted, then you may be pulling -5F air under the slab during a cold snap, which is chilly, and may even freeze the soil. Therefore it's probably not a good idea to tie the two together.

    Another thing to consider is when you are using air conditioning, there is zero stack effect or negative stack effect. So in hot climates, you can bet a passive system won't work.

  5. User avater GBA Editor
    Martin Holladay | | #5

    Response to Kevin Dickson
    Kevin,
    To respond to your second question first: although the stack effect varies with the weather, and will obviously be greater in cold weather than hot weather, the recommendations for new homes remain the same. Start with a passive system; then test the indoor air; and don't install an exhaust fan unless testing shows the fan to be necessary.

    Researchers have looked into the question of whether active radon mitigation systems contribute to slab cooling. I reported extensively on the topic in an article I wrote for the March 2007 issue of Energy Design Update.

    In fact, there is no single source for the makeup air that is drawn to the subslab area to replace the air exhausted by a radon mitigation fan. The entire question of makeup air is far more complicated than it first appears. I interviewed Joe Nagan and Brad Turk at length on this topic.

    Here is a quote from my 2007 article: "[Joe] Nagan admits that the source of the fan’s makeup air is somewhat mysterious. “If in fact the makeup air is coming from the soil outside the foundation, why aren’t we chilling the crap out of these slabs?” asks Nagan. “I’ve measured the temperature of the slabs, are they’re warm.” According to [Brad] Turk, soil air reaching the crushed stone under a slab usually has a temperature of about 50°F, so in most cases soil air does not significantly chill a basement slab. “Around buildings, there can be a few direct pathways that connect the outside air to the crushed stone under the slab — for example, the shrinkage gap next to the foundation where they backfill,” says Turk. “A subslab depressurization system can pull the air down next to the foundation wall, and in some cases you can see the air pulled down by using a smoke stick. But the path that the air follows is almost unknowable — there are so many permutations and pathways, so many materials that are not homogenous. You don’t have an engineered channel directing the air. It is possible to have situations where you chill the slab — if air can find a short path to the subslab aggregate — but in most cases the path is so tortuous, you’re not going to see any chilling of the slab.”

    Needless to say, I have long argued in favor of the installation of a continuous horizontal layer of rigid foam under a basement slab, in order to keep the concrete slab at room temperature. This insulation reduces the condensation risk in the summer, allows carpeting to be installed if desired, and greatly reduces the chance of mold. Moreover, it addresses your concern -- a concern which may in any case be groundless.

  6. Nick Welch | | #6

    Humidity
    The dehumidification aspect is fascinating. It seems that a radon exhaust fan could be a good solution for homes with basement humidity issues, and that maybe this should be attempted before resorting to a dehumidifier -- but I've never seen it mentioned in such discussions. Even if you still need a dehumidifier, the radon fan could reduce its run time -- and energy use -- enough to make it worth the trouble.

  7. User avater GBA Editor
    Martin Holladay | | #7

    Response to Nick Welch
    Nick,
    I agree that the idea is intriguing, but we need more research on the issue.

    The last time I interviewed experts studying the connection between active radon mitigation systems and basement humidity levels, they shared many anecdotes, but admitted that we need more data on the issue, in a variety of climates, before we can draw firm conclusions.

  8. Nick Welch | | #8

    A new rule of thumb
    Your wattage and annual cost examples also made me realize that if you run something 24 hours a day, through a quirk of math, you can roughly estimate that its annual cost is its wattage in dollars. 20w fan = ~$20/yr. (assuming electricity rates around 11.4 cents)

  9. User avater
    Dana Dorsett | | #9

    Slab depressurization & dehumidfication.
    Active slab depressurization for radon can only mitigate indoor humidity due to groundwater penetration, which would be pretty small on a house built with vapor barriers under the slab. From a simple energy-use point of view, there's no way running a 60-100W fan 24/7 is anywhere near as efficient a means of reducing indoor moisture levels as running a compressor based dehumidifier under dehumidistat control.

    BTW: Not mentioned in the blog article, using active heat recovery ventilation to swap out the air in the basement/house at reasonable rates is a common method of radon abatement that doesn't involve slab depressurization.

  10. User avater GBA Editor
    Martin Holladay | | #10

    Response to Dana Dorsett
    Dana,
    I should have made it clear that the reports of lower humidity levels in basements with active radon mitigation systems refer to older homes without poly under the slab. Hopefully, if you are building a properly detailed new home, you won't have a damp basement -- whether or not you ultimately install an active radon mitigation system.

    If readers are interested in learning more about the HRV option, you can read Peter Yost's description of retrofit work at his own house in the following two articles:

    Vapor Barriers, Radon, Basement Slabs, and VOCs

    Deep Energy Makeover

  11. Aj Builder, Upstate NY Zone 6a | | #11

    Radon hogwash
    Butter bad...

    Radon hogwash

    Butter bad... Eggs bad....

    Life so far leads to one place, death.

    And.... Someday,... The sky.... Will fall.

    Look for a Lake Placid Ubu... Next time yaa go lookin for fun instead of cringing in the corner from fear of an invisible gas death.

  12. Mike Strevell | | #12

    Electric radon meters, slab+crawlspace?
    Martin - what are your thoughts on the $130 Safety Siren Pro Series 3 electric radon meter vs the $30 test kits?

    My basement is half-finished (slab), and half crawlspace, and my radon level is right at 4.0. Would I be better to start by depressurizing the slab, or covering/venting the crawlspace?

  13. User avater GBA Editor
    Martin Holladay | | #13

    Response to Mike Strevell
    Mike,
    I am not familiar with the electric radon meter you mention, so I can't help you with a product review. Perhaps another GBA reader has an opinion.

    If your crawl space floor is exposed dirt, the obvious first step would be to cover the dirt with a seamless layer of polyethylene and to seal the perimeter of the polyethylene to the crawl space walls. It might also be useful to build an airtight wall between your basement and your crawl space. Once these measures are completed, you can test the air in your basement again and see if your radon level has dropped.

    After all, these measures require no electricity or maintenance, and are therefore preferable to installing a radon mitigation fan.

  14. Carmine Vasile | | #14

    More about Radon
    Although the U.S. Environmental Protection Agency (EPA) advises homeowners to test air in their homes for the presence of radon, few know Congress excluded radon & one of its parents (Uranium) from radionuclide regulations for public water suppliers since 1976. If the EPA classifies a system as a non-transient non-community water system (NTNC) – even if it contaminated by on-site dumps like the Plum Island Animal Disease Laboratory on Plum Island, NY, they are not required to perform radiological sampling. Private well owners are required to perform their own tests. Plum Island used to be connected to Long Island, which has many public wells with over 300 picocuries per liter (pCi/L) of water. Although a Maximum Contaminant Level (MCL) of 300 pCi/L was proposed over a decade ago, Congress continued to exclude radon in its 2000 Amendment of the Safe Drinking Water Act; when it t began limiting total Uranium to 30 micrograms per liter of tap water. Since then indoor air pollution climbed as homeowners continued to plug air leaks to save energy. [1]
    If radioactive water is a source of radon gas, vents in the incoming water line should be installed -- as I did when I installed the first GFX wastewater heat recovery system in April of 1980.
    __________________
    [1] RADIONUCLIDE MCLs: On July 9, 1976, EPA promulgated 40 CFR Part 141 Drinking Water Regulations:Radionuclides (1976 MCL rule). This 1976 MCL rule included the following MCLs: 5 pCi/L for radium-226 and radium-228 combined; 15 pCi/L for gross alpha particle activity (including radium 226, but excluding uranium and radon); and a concentration that produces a dose equivalent of 4 mrem/yr or less to the total body or any internal organ for the sum of the doses from man-made beta particles and photon emitters. A list of radionuclides that are addressed by the gross alpha MCL are provided in Attachment A to today’s memorandum. Also, provided in Attachment B to today’s memorandum is a list of radionuclide concentrations calculated using the 4 mrem/yr beta particles and photon emitters MCL standard. On December 7, 2000, EPA amended 40 CFR Part 141 (65 FR 76708, December 7, 2000) National Primary Drinking Water Regulations; Radionuclides (2000 MCL rule). This 2000 MCL rule established requirements for uranium, and retained the existing requirements for combined radium-226 and radium-228, gross alpha particle radioactivity, and beta particle and photon radioactivity. The 2000 MCL rule did include MCLGs of zero for the last four contaminants (see 40 CFR § 141.55). [From EPA Directive no. 9283.1-14]
    Although the U.S. Environmental Protection Agency (EPA) advises homeowners to test the air in their homes for the presence of radon, few know Congress excluded radon & its one of its parents (Uranium) from radionuclide regulations for public water suppliers since 1976. If the EPA classifies a system as a non-transient non-community water system (NTNC) – even if it has on-site dumps like the Plum Island Animal Disease Laboratory on Plum Island, NY, they are not required to perform radiological sampling. Private well owners are required to perform their own tests. Plum Island used to be connected to Long Island, which has many public wells wells with over 300 picocuries per liter (pCi/L) of water. Although a Maximum Contaminant Level (MCL) of 300 pCi/L was proposed over a decade ago, Congress continued to exclude radon in its 2000 Amendment of the Safe Drinking Water Act, when it began limiting Uranium to 30 micrograms per per liter of water -- even as indoor air pollution climbed as homeowners plugged air leaks to save energy. [1]
    If radioactive water is a source of radon gas, vents in the incoming water line should be installed -- as I did when I installed the first GFX wastewater heat recovery system in April of 1980.
    __________________
    [1] RADIONUCLIDE MCLs: On July 9, 1976, EPA promulgated 40 CFR Part 141 Drinking Water Regulations:Radionuclides (1976 MCL rule). This 1976 MCL rule included the following MCLs: 5 pCi/L for radium-226 and radium-228 combined; 15 pCi/L for gross alpha particle activity (including radium 226, but excluding uranium and radon); and a concentration that produces a dose equivalent of 4 mrem/yr or less to the total body or any internal organ for the sum of the doses from man-made beta particles and photon emitters. A list of radionuclides that are addressed by the gross alpha MCL are provided in Attachment A to today’s memorandum. Also, provided in Attachment B to today’s memorandum is a list of radionuclide concentrations calculated using the 4 mrem/yr beta particles and photon emitters MCL standard. On December 7, 2000, EPA amended 40 CFR Part 141 (65 FR 76708, December 7, 2000) National Primary Drinking Water Regulations; Radionuclides (2000 MCL rule). This 2000 MCL rule established requirements for uranium, and retained the existing requirements for combined radium-226 and radium-228, gross alpha particle radioactivity, and beta particle and photon radioactivity. The 2000 MCL rule did include MCLGs of zero for the last four contaminants (see 40 CFR § 141.55). [From EPA Directive no. 9283.1-14]

  15. Roger Anthony | | #15

    Radon gas more important Radon daughters.
    As radon itself decays, it produces new radioactive elements called radon daughters or decay products. Unlike the gaseous radon itself, radon daughters are solids and stick to surfaces, such as dust particles in the air. If such contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.

    Despite its short lifetime, some radon gas from natural sources can accumulate to far higher than normal concentrations in buildings, especially in confined areas such as attics and basements. This is especially true of basements where the build up of radon daughters presents an added danger to young children who tend to play on the floor.

    The highest average radon concentrations in the United States are found in Iowa and in the Appalachian Mountain areas in south-eastern Pennsylvania

    Many cities within the state, such as Iowa City, have passed requirements for radon-resistant construction in new homes.

    As mentioned above. Gases can enter the building via cracks and joints that form within the structure, so a flexible polyethylene membrane should be selected that is capable of accommodating movements in the structure without fracturing.

    An impervious polyethylene membrane should always be applied as a damp proof membrane above a ground floor slab to stop ground moisture reaching the upper surface of the floor.

    As mentioned above there are two options passive and active, an active solution will incur running and maintenance costs for the life of the building.

    In high active Radon Gas areas an active solution should be installed, but not connected until the amount of Radon gas entering the building has been ascertained. Passive systems with no running costs are to be preferred.

    Passive protection consists of a complete airtight seal integrated within the ground floor and walls. A standard polyethylene 1200 gauge damp proof membrane should be adequate if carefully sealed along all joints.

    An active solution, as the above illustration may be required, but if you access one of the several Radon gas maps, you will be able to ascertain if building in a different place would be preferable.

    Here is a map of the USA showing concentrations of Radon gas, there are many others available on the net. http://www.radon.com/maps/

    Granite areas are of particular risk

  16. Glenn Ravdin | | #16

    Radon and Ledge
    Martin,

    My basement is mostly ledge covered with Basement Systems barrier. Only about 1/3rd of my basement is bare concrete floor. The ledge is sedimentary rock, mostly slate and very hard, which is why it couldn't be excavated when we built in 1988. I'm six months into testing now.

    Is ledge more or less likely to generate radon? I have found conflicting information on the Internet.

  17. User avater GBA Editor
    Martin Holladay | | #17

    Response to Glenn Ravdin
    Glenn,
    It really hardly matters whether, on average, exposed ledge is more or less likely to cause a radon problem than concrete. You don't care about averages. All you care about is the radon level in your home.

    If you are now testing, you're doing the right thing. Once you have the test results, you'll have the information you need to make a decision about radon mitigation.

  18. Sean MacKinnon | | #18

    Can radon be distributed?
    Hi - I understand that typically radon levels are higher in basements but I was wondering if circulating air in a house may increase radon levels on other floors of the house. I have an air purifier connected in series to my HRV supply but because the air purifier (HEPA filter) moves more air than the HRV, I have an open tee in the basement where they are connected. This pulls from the basement to make up the difference. Am I increasing levels in other parts of the house? Thanks.

  19. User avater GBA Editor
    Martin Holladay | | #19

    Response to Sean MacKinnon
    Sean,
    If your basement has elevated levels of radon, it stands to reason that an HVAC system that distributes air from your basement to upper floors may be helping to raise the radon levels in upper floors.

    This hypothetical problem would only occur in a house with elevated levels of radon in the basement. As noted in my article, the only way to tell whether you have elevated levels of radon is to test the air in your house.

  20. Joe Suhrada | | #20

    T pipe for passive system
    At the T, how many feet of perforated pipe are needed in each direction?

  21. User avater GBA Editor
    Martin Holladay | | #21

    Response to Joe Suhrada
    Joe,
    As far as I know, the length of the horizontal perforated pipe used for a passive radon system is not specified by any standard or regulation. Common sense should prevail.

    If the layer of crushed stone is clean and continuous, gases should move fairly readily through the crushed stone layer, even if the perforated pipe does not extend to every corner of the home's footprint. Remember, though, that perforated pipe is cheap.

  22. Andy Nels | | #22

    Testing virgin earth, pre-build
    Has anyone tried to test their planned building site by covering a charcoal tester with a large plastic box or trash can? If me, I would. Like dig a 3' deep by 2' wide hole, place tester in bottom on a short 6" stand of some sort, and do 5 of them ($9 each with lab included online stores). In a cross pattern across proposed build site. If electricity is available use an electronic tester and have initial results 48hrs. $70 online. I read an article of a fella who tested his land all the time in PA and had levels all over the place that followed patterns. However, I think the fake science that has propped up too many jobs and product is hard to argue with at this point, lol. Only time will tell after comparisons are made and only if objectively at that. I don't think it's being tracked so likely won't ever know if it's unhealthy or benign.

  23. User avater GBA Editor
    Martin Holladay | | #23

    Response to Andy Nels
    Andy,
    I have never heard of that method, and I'm skeptical that the results from such a test would correlate with radon levels in a building.

  24. Greg Labbe | | #24

    Mechanical ventilation
    This is one more reason to build super air tight building enclosure - including the slab. The air-tight building necessitates a proper living space ventilation system, preferably a balanced E/HRV. I'd be curious to know if really air tight homes (ie passive house levels) are less predisposed to soil gas infiltration. Any data out there?

    To cut potential thermal losses and reduce electricity cost of active, motorized systems:

    1- It would be nice to know; what's the minimum amount of depressurization to be applied sub slab? Presumably greater pressure would be needed in wintertime as stack effect negatively depressurizes the basement. Would -5Pa under slab less than the basement at the worst time of the year be enough or even 10Pa? Establishing that, one could 'tune' or 'size' an appropriate depressurization system. I suppose one could also 'enclose' the crushed stone with a drain-able, airtight fabric to create a buffer zone between the soil and the slab which could be depressurized with significant fewer CFMs.

    2- Does the system have to run through the house and penetrate the air barrier system multiple times? Can't it be run outside of the building envelope if mechanically depressurized?

  25. User avater GBA Editor
    Martin Holladay | | #25

    Response to Greg Labbe
    Greg,
    Many of the questions you asked are answered in the article on this page.

    I wrote, "High radon levels are possible in new homes as well as old homes, and in tightly sealed homes as well as leaky homes." There is no correlation between the tightness of a home and indoor radon levels. To read an article about a very tight new home that had radon problems, see Radon and a Passive House.

    Come to think of it, here's another example: Finishing Touches for a Pretty Good House in New Hampshire.

    There are two reasons that it's best to keep a radon vent stack inside the home's thermal envelope:

    1. This method allows the exhaust fan (if one is needed) to be installed in the attic, where it is protected from the weather. (Otherwise, it would have to go outdoors, since you never want to install a radon exhaust fan inside a home's thermal envelope.)

    2. If this will be a passive radon mitigation system, keeping the stack warm in winter aids the stack effect and improves radon removal.

    If you want to experiment with different cfm rates for a radon mitigation fan, you can. Get a variable-speed fan, and experiment away. Just make sure that you check indoor radon levels to be sure that you are hitting your target.

  26. Sacie Lambertson | | #26

    sand under slab for radon mitigation
    Would sand under the slab instead of gravel work for allowing the radon to flow freely? For a crawl slab our contractor wants to put down insulation over the top of gravel because he is worried about gravel penetrating the 20 mil poly covering he will place before pouring a rat slab. Can't believe this is likely. Comments?

  27. User avater GBA Editor
    Martin Holladay | | #27

    Response to Sacie Lambertson
    Sacie,
    For the horizontal movement of soil gases, you want crushed stone without fines, not sand.

    20 mil poly is thick stuff. I've installed ordinary 6 mil poly over crushed stone without any problems.

  28. User avater
    Ethan ; Climate Zone 5A ; ~6000HDD | | #28

    I have heard that radon tests
    can vary wildly based upon prevailing winds, time of day, time of year, etc. I have also read the full reports and personally believe that if you don't smoke radon isn't a problem. Also, shouldn't tight vapor and air sealing of slabs and perimeters mitigate infiltration of any radon gas into the home? Why is radon gas more likely to get through a subslab air barrier than a pvc pipe running the full height of a home?

  29. User avater GBA Editor
    Martin Holladay | | #29

    Response to Ethan T
    Ethan,
    Q. "I have heard that radon test [results] can vary wildly based upon prevailing winds, time of day, time of year, etc."

    A. Yes. I explained that in my article: "Radon levels can fluctuate from day to day, so long-term tests tend to be more accurate than short-term tests. Most homeowners start with a short-term test. If the results are near or above 4 picocuries per liter, it’s worth following up with a long-term test."

    Q. "Why is radon gas more likely to get through a subslab air barrier than a PVC pipe running the full height of a home?"

    A. I think the type of PVC pipe you are describing -- "a PVC pipe running the full height of a home" -- refers to one of the important components in a passive radon mitigation system. The reason that builders are advised to install a passive radon mitigation system is precisely for the reason you guessed: because the vertical PVC pipe provides a route for escaping soil gas, thereby reducing the likelihood that dangerous levels of radon will enter your basement.

  30. Keith H | | #30

    Radon anecdotes: dehumidification and electronic radon monitor
    Dehumidification:
    I'll pass on an anecdote. Dirt 4' crawl space 2 story house, dry climate zone 5. Ground water intrusion during a flood event resulted in a musty smell that could not be dispelled with fans, filters, and dehumidifiers (no visible mold). Had a 'professional' radon system (collection tube, barrier, and active fan) installed. Smell disappeared quite quickly along with the humidity and radon.

    Safety Siren Pro Radon detector:
    I have two family members who use this device for their homes so I have been able to borrow and play with one quite a bit. I highly recommend it. It is sensitive enough to indicate differences in radon between basement and first floor and to register small changes in radon. We vetted the results vs mail-in radon tests twice and the results were very similar. If you have a desire or need to monitor your radon levels regularly or to insure a system is still working, it seems like a reliable and cost effective solution. I don't know about other radon monitors.

    Personally, I believe radon is a very understated risk as the #1 cause of lung cancer in non-smokers. It is also one of the easier cancer risks to mitigate.

  31. Andrew Bater | | #31

    Additional anecdote(s) & radon monitor(s)
    I have a sub slab passive radon vent; it was created by connecting a riser to the perimeter Form-A-Drain footer system. In hindsight I think a dedicated piping system under the center of the slab is better.

    Several multi-day radon tests indicated that we had levels in a ground floor bedroom slightly above 4 picocuries. Those tests were done in the winter when the windows and doors were guaranteed to be closed.

    Not long after the aforementioned tests I purchased an Airthings Corentium radon monitor so I could investigate the situation further.

    I was about to put in an active fan system, either using the existing riser (I even bought the fan), or by repurposing another sub slab drain line I have. Asked some questions here on GBA; the responses made me realize I might be jumping the gun.

    The anecdotes:

    1. I took a nap in that bedroom one winter day. That room is nestled in the corner of our foundation, gets passive solar gain, and has radiant heat; it's very toasty. Lying there I realized the room was actually stuffy. It dawned on me that in wintertime, when I was taking these radon samples, I had our high velocity air conditioning system totally disabled so there was no air movement. Set up the air handler so it could provide a constant low air flow (sans cooling) and voilà, the radon levels dropped. "Dilution Is The Solution".

    2. With a real time electronic monitor on hand, I have definitely seen where radon levels are higher when the ground outside is saturated with rain etc. Makes me wonder how many unlucky folks fail short duration radon tests done for real estate transactions, where just a few sunny days later they might pass.

    3. Airthings announced another monitor with alarm, like the Safety Siren. I got an early production run unit. Seems to track their earlier device, screen shots attached. https://airthings.com/wave/

    4. I am running four long term Accustar Alpha test kits, two next to the Corentium monitor and two upstairs. I am seven months in to a full year test duration. Will report back.

    5. Segal's law: "A man with a watch knows what time it is. A man with two watches is never sure." OK, I am guilty, but the measurement data is starting to sync up.

  32. Andrew Bater | | #32

    Update on Corentium Radon Monitors, First Alarm on Wave Unit
    An unfamiliar icon popped up on my cellphone today; I clicked on it and lo and behold it was the Airthings Wave unit telling me that the radon level was high on my ground floor: "Air Quality Is Poor"

    Surprised, but not surprised, we are into weather just above the freezing mark (heat is on), and it's raining/snowing and windy. 1.35" of precip so far this weekend and it's been wet in general the last few weeks. So this is "perfect radon weather".

    Again though our long term average is below the 4 picocurie standard as can be observed on the screenshots of the regular Corentium monitor.

    Just a few more months till I conclude my year long "test".

  33. Rick Evans | | #33

    Questions about Radon Pipes
    Hello All,

    I'm installing a passive radon mitigation system (new construction) under a slab. Just curious what kind of pipes people are using under the slab.

    1.) Do the pipes have to be PVC? Or will the HPDE "triple wall" pipe suffice? (like this: https://www.homedepot.com/p/4-in-x-10-ft-2-Hole-Triplewall-Pipe-4520010/100191022 )

    2.) does the number of holes/preforations in the pipe matter? Will a 'two-hole' arrangement be okay? Or must the pipe be perforated on multiple sides?

    Slab is just for basement and will be non-load bearing. Have 10" of crushed stone under slab. Once pipes are in, there will be 6" of EPS and a 15 mil vapor barrier.

    Thank you!

  34. User avater GBA Editor
    Martin Holladay | | #34

    Response to Rick Evans
    Rick,
    I'm not very familiar with HPDE pipe. I haven't seen any warning in online sources that HPDE won't work for a radon system.

    That said, most radon systems use PVC. The conservative approach is to follow conventional practice and stick with PVC. (I assume that you are asking because the HPDE pipe is cheaper?)

    Certainly the vertical riser should be PVC with glued joints, so it makes sense to choose compatible materials.

    I don't think the number of holes matters.

  35. Rick Evans | | #35

    Excellent- Thank you Martin!
    Thanks so much Martin- I will go with PVC.

    I haven't actually priced out the PVC yet to compare it to the HPDE pipe... My local lumber yards don't seem to carry perforated PVC at the moment so that means I will have to visit the local plumbing supply.

    Only professional contractors visit the local plumbing supply. Every time I go there they know intuitively that I am an amateur and proceed to give me a hard time about everything. I think its my Prius that gives me away...

    Anyway- thanks again Martin, as always!

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