GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Thoughts on Radon

plumb_bob | Posted in General Questions on

I recently sat through a presentation on radon, presented by a nuclear science specialist, and it was very thought provoking.

One of the main takeaways was that structure fire deaths average +/- 300 annually in Canada, and they estimate annual deaths from radon at more than 3000. So if these numbers are correct it shows where prioritization for building codes should be.

Much of the data comes form long term studies of uranium miners, where the level of radiation is measured and compared to the incidence of disease.

Our codes in BC call for a sub slab depressurization rough in (if in a known radon area), with the thought that an extraction fan can be added after the fact if needed, but the actual requirements for the system are vague and leave room for poor installations.

I personally am going to be paying more attention to this subject moving forward, and testing my own home.


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member
    Michael Maines | | #1

    I agree that it's an important and under-appreciated topic. Here's what I wrote about it a few years ago:

    There have been a lot of articles about it here on GBA as well:

  2. kbentley57 | | #2

    About 1.5 years ago I finally got around to buying an air things wave plus. It revealed I had moderately high radon, at different times of the year. Sometimes it was around 2, other times I saw as high as 7. I activated my passive system and like magic, it’s now hovering around 1 consistently.

    Since, the advice I’ve been giving people who already have a passive system in place is “don’t test, just install a system”.

    A radon mitigation fan, 25’ of 14/2 and a single gang box, receptacle and faceplate all cost less than a good radon/indoor air quality meter. Or at least that was the case a year and a half ago.

    Here’s a screenshot of my AirThings radon section. Can you find the point on the graph where I installed the system?

    1. 5Stud | | #9

      I think I can!
      Not sure what CZ you are in but your numbers start to ramp up in September?

      1. kbentley57 | | #11


        I'm in northern Alabama, on the edge of 3A and 4A. You're correct. I had a high spot or two in the summer, but for the most part it started rising in August and stayed high for the rest of the year. That's what prompted me to install the fan.

        For the curious: Here's a few pics from my install. It was pretty smooth, other than crawling around in the attic to get to my passive vent. The fan itself is inaudible from more than 10 ft away, and it draws about 50W continuous. It pulls about 1.4" H20 according to the manometer.

        1. DennisWood | | #13

          Kyle, that looks like a tidy install...nicely done :-) My one suggestion would be to move that manometer down inside your house as an easily accessed visual indication that the system is running. Of course, if you're actively monitoring radon gas levels, you'd likely be aware of it fairly quickly even without the manometer.

          1. kbentley57 | | #14

            That's a good suggestion Dennis!

            I wish it would have been easier to get to, but the wall it's in is crowded out by stuff that would have been harder to move than it was worth.

  3. DennisWood | | #3

    I also just added a Wave Plus to our setup here at home to add another CO2 sensor and VOC input to the automation system. I chose this device specifically as it also tests for radon, with a decent accuracy over longer periods confirmed by at least one published study. We had never tested in our basement area so I’m somewhat reassured to see levels averaging 1.6 so far. That said, a minimum observation of 30 days is advised, so it is too early to draw any conclusions.

    I’ve been using CO2 levels alone to ramp ventilation rates based on occupancy but am now adding VOC and radon into the automation code. Adding inputs to the system along with variable ventilation rates has been quite an educational process in the pursuit for an efficient IAQ system.

    1. gbcif | | #4

      I'm in Southern VT and I found out I had a radon reading of over 20. I followed the instructions creating a system without piping under the slab under the slab. I started with a 6-in hole that I drilled many small pilots and knocked out the chunk with the concrete hammer. I removed several 5 lb spackle buckets worth of soil one hand at a time and also by using a shop vac. I routed 4-in PVC internally in the house and terminated it through the roof. The fan I chose was one of the variable fans and I have it tuned down right now to about 20% operation and I'm getting a reading of one to 1.3 study. I chose the fan that's very well because I didn't have the equipment to size the fan properly. When I had the fan fully turned up you could hear the air swishing through the cinder block part of the foundation! My numbers were zero when it was running full speed. As it's presently operating I don't even notice the electricity consumption on my meter it's very low.

  4. plumb_bob | | #5

    GBCIF, that is a great result. I may add a fan to my radon piping as well, depending on what comes back from the radon test.

  5. StephenSheehy | | #6

    I'm just a natural skeptic, I guess. But extrapolating from uranium miners to homeowners seems like a stretch.
    That said, placing a radon collection pipe under the slab and running it through the roof is pretty simple and inexpensive, so there's no reason not to do it.

    1. 5Stud | | #7


      This is the first time I have heard the uranium miners extrapolation proposal and I agree, a stretch
      I know that there were some studies of midwest farm wives that had some fairly significant correlation numbers.

      It is code in Canada to have a 4 inch radon rough-in pipe under slab and also visible sealing of all slab penetrations including the perimeter slab to foundation wall junction

      1. Expert Member
        MALCOLM TAYLOR | | #10


        I don't know what the requirements are in every province, but in Ontario and BC the mitigation measures are limited to projects in known radon areas.

    2. Expert Member
      Michael Maines | | #8

      Dana Dorsett, who used to post here a lot with solid information, had written a few times about how far extrapolated radon limits are. Apparently in some parts of Europe they're ok with something like 8 pCi/L whereas North American cancer and radon foundations recommend 2 as a limit. I don't think there's any doubt that radon causes cancer; they just can't pin down the risk precisely.

  6. DennisWood | | #12

    I've looked over a few of the research studies and would agree with what Michael says regarding radon levels. There is however strong evidence of much higher cancer risk where the combination of smoking and higher long term radon exposure exists.

    This one is a good read:

    "The European pooling study by Darby et al. is the most representative pooled analysis from 13 European case-controlled studies and demonstrated a linear and statistical increase of 16% (range, 5–31%) of lung cancer risk per 100 Bq/m3 of indoor radon "

  7. plumb_bob | | #15

    In BC the radon mapping has been updated with more areas within the zones that require a rough in. This apparently will be updated in our code, of which a new edition is anticipated in late 2023. I am curious to see if there will be more specific requirements for the rough in system, such as limiting the number of bends and turns of the pipe that runs up through the roof. Right now you could build it with as many elbows as you want, which reduces the effectiveness of a passive extraction system.

    1. Expert Member
      MALCOLM TAYLOR | | #16


      It's a bit worrying. I have never included radon mitigation in any house I've designed or built here (including my own slab in grade) because of the reassurance that there was no radon risk on Vancouver Island. If the revised mapping shows this is necessary here I'm not sure what I'll do.

  8. StephenSheehy | | #17

    The question I wrestle with is where does radon fall on the list of health risks associated with homes? Worse than cooking with gas? Worse than falls on stairs? How about VOCs in paints or formaldehyde in furniture?
    If we have $1500 to spend making a house safer for occupants, is radon mitigation the best place to spend it?
    Recently in Maine, we've been experiencing what is being presented as a public health calamity caused by PFAS that were in sewage sludge that had been spread on farm fields as a cheap fertilizer. Dairy farmers have had to stop milking their cows. Other farms can't sell crops. We can now test PFAS to parts per trillion. Is this the worst public health problem we have, such that we should spend millions of dollars paying the unfortunate farmers?
    We seem to lurch from one disaster of the week to another. We all remember that billions were spend on asbestos removal in every office and school in the country. Nobody questioned whether removal made sense, because everyone knows asbestos is bad. But was asbestos buried under finished walls and ceilings so dangerous it had to be removed, no matter the cost?

    1. Expert Member
      Deleted | | #19


      1. Deleted | | #20


      2. StephenSheehy | | #21

        Michael. I'm not suggesting that PFAS chemicals are benign. But we're telling dairy farmers they can't sell their milk because it is contaminated with levels of PFAS that, until recently, were undetectable. Yet we wear GoreTex. We use non stick pans. When we have surgery under general anesthesia, we inhale PFAS at levels orders of magnitude higher than we see in milk or food.
        PFAS chemicals have been especially associated with serious illnesses among firefighters because firefighting foam contains very high levels of PFAS chemicals.
        My argument is simply this: We need to make informed judgements about environmental hazards based on good science. I'm not convinced that we have good science about the risks of radon or PFAS to the extent that we should assume they represent the most serious public health risks we face.
        I'm truly sorry about your father-in-law.

  9. plumb_bob | | #18

    The presentation was by the BC Lung Foundation, and their website has much of the info including the mapping.

    I think radon mitigation in a new build is a low hanging fruit, since most of the under slab components including course granular material and sealed poly sheet are required anyways for other functions. All you are adding is some strategically placed piping from soil to roof for a rough in, and an inline electric fan for a true extraction system. The rough-in literally adds almost nothing to a build cost.

    The standard detail I see on large commercial, MURB, and institutional is dedicated radon suction pits, which are still cheap and easy to build relative to everything else.

    If the level of harm is even 1/2 what recent studies are showing then these investments are well worth the cost in my opinion, especially compared to the marble back splash or other stupid shit people put in their houses.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |