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Community and Q&A

Dual passive radon remediation systems?

Bruce_Davis | Posted in Green Building Techniques on

I read the GBA article “All About Radon.”  My new construction is utilizing the techniques Martin recommends.  My foundation is a walk-out, 12 ft high concrete in the front, stepping down to all frame in the back.  Slab is about 3500 sq ft, 88 ft wide and averages about 40 ft deep.  This includes a suspended four car garage (2+2 tandem).

The suspended 1500 sq ft is sort of separate from the rest of the basement with three door openings in the concrete between them.  Since there is a continuous footer between the two sides, the 4 inch gravel under the slab will also be separated (maybe should have put some drain tile under the footers there, but didn’t think of it).  Seems to me then, that I should have two independent 4 inch “T” passive radon systems, one on each side of the house.  Not only will the gravel be separated, but they will be about 82-85 ft apart.  Do the dual systems make sense?  Thanks.

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  1. Jon_R | | #1

    What problems do you envision with a single system? Say with a single, mid-section mounted fan and pipes to each slab?

    1. Bruce_Davis | | #3

      Based on the article and trying to keep it passive, that would introduce horizontal pipe & fan. Maybe that's better, I don't know.

      1. Bruce_Davis | | #6

        I do see a spot where that might work. I could go on each side of the 1 ft thick wall. That would put pipes about 3 ft apart. I assume they would meet at top of foundation and go up through wall there. Would that be vertical enough? Thanks.

  2. GBA Editor
    Martin Holladay | | #2

    Your description is a little confusing. A sketch would help.

    Your slab is 40 feet deep? What does that mean?

    1. Bruce_Davis | | #4

      Deep means front to back. I'll try and add sketch later. Thanks.

  3. Bruce_Davis | | #5

    See attached photo of footers. Top of photo is front of house with suspended garage on the right side of the middle footer running front to back. The back footer drops for a buried wall. You can see how the sub-slab gravel will be divided about 60/40.

    Looking at pic, radon stacks would be at the upper left & upper right corners. Both are unfinished utility areas. Under the left & center garages will be a home theater. One side or the other of that dividing footer/wall will be finished.

  4. GBA Editor
    Martin Holladay | | #7

    I'm not a radon mitigation specialist. You may want to consult one for a more educated answer.

    If you can find a way to have a single vertical riser serving both sides of the foundation, that approach would have one advantage: if you even need to convert your passive system into an active system, you would only need one fan. But two separate systems would also work.

  5. jackofalltrades777 | | #8

    Whatever methodology you do, you want to make sure it is done right. The #1 cause of lung cancer in non-smokers is Radon Gas. It doesn't happen overnight but years of buildup and residing in a home with improper mitigation increases your risk.

    1. Expert Member
      Dana Dorsett | | #12

      That is it's the #1 cause of lung cancer in non-smokers, if using a linear response no threshold model for radiation exposure. That model says that ~21,000 of the ~157,000 lung cancer deaths in the US are caused by radon, but there are really big error bars on that 21K number. The model commonly used by health organizations and regulatory bodies in the US and elsewhere are primarily built on studies of occupation exposure by underground miners, at much higher levels. But underground miners are also exposed to other aggravating factors, such as inhaled silica and toxic metal ores, etc.

      There are a few indicators that stand the conventional wisdom regarding the zero-threshold linear model on its head. There are fewer lung cancer cases per capita in higher radon level counties in the US in large statistical studies, and looking at the smoking factors, that isn't explained by lower smoking rates in those counties. The most radiation exposed large cohort general population in the world are in Kerala India (mostly from natural radon), happens to be the state that has the longest lifespan statistics, but it is also one of the poorer states.

      The effects of very low dose radon are hard to measure directly in the real world- the error bars are large at the thin edge of the low-lower-lowest dose wedge, but it's not truly linear even at higher exposures. Biological responses to radiation vary- the same average annual dose delivered in intermittent higher intensity doses are different from continuous low doses, when the total annual dose ends up the same. Nuclear industry workers have higher exposures, but lower cancer rates. The simple model is simply wrong, but without a better model, we can't say for sure HOW it's wrong, and it's what we're stuck with.

      The reason the EPA's 4.0 pCi/L remediation level is only a RECOMMENDATION rather than a REGULATION is all about those uncertainties. In Europe even the most stringent countries set remediation thresholds higher than that, and like the US, they are usually recommendations, not regulations. Canada's remediation threshold is 200 Bq/m3, (=5.4 pCi/L), which is the World Health Organization's (WHO) recommendation.

      Sweden is one of the first (only?) countries with mandated limits on radon for new residential housing currently set to half the WHO level, now set to 100 Bq/m3 (=2.7 pCi/L). Is that the right & most reasonable number? Who knows?

      So at the bottom line, radon MIGHT be the largest cause of lung cancer in the US for non-smokers if the model is perfect, but it might not actually be true. It's even possible that low-dose radon at some levels is somewhat protective against some cancers, with some studies in the literature indicating a few 10s of pCi/L might be the sweet spot for lowest risk, but it's really quite hard to measure, with low certainty about what the true dose-response is when it's down in the statistical noise, and little ability to control for other factors.

      If after all is said and done your house tests at some higher number than 2.7 pCi/L or 4.0 pCi/L or 5.4 pCi/L don't freak out. You (like most people in Kerala) probably have other, bigger health risk factors to worry about. Of the 2.6 million deaths per year in the US, even the estimated 21,000 radon induced cancer deaths per year is less than 1%.

  6. Expert Member

    Just out of curiosity, why are some of the footings not continuous? There seem to be gaps where they aren't connected.

    1. Bruce_Davis | | #10

      The footing to nowhere at the top center of photo is for stair framing, not foundation. The three at the bottom of the photo are boxes that drop 6 ft for a buried wall to keep me from sliding down the hill (along with 34 piers).

  7. Bruce_Davis | | #11

    The only flaw with my plan to join the two up in the middle was aesthetics. It would put a 4" vent pipe smack in the middle of the front of the roof. Went with Plan B: one near the top right corner of photo; the other at the bottom left corner of photo.

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