Radon mitigation question


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Old 12-01-21, 04:08 PM
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Radon mitigation question

Hi.

In my old house the basement was unfinished and the crawlspace was open to the basement.

In my new house the basement is finished and drywall separates the finished basement from the crawlspace.

Both are 1920s construction, a mile from each other. Neither had anything more than black plastic sheeting over the dirt in the crawl. Certainly no proper encapsulation, In the old house the plastic sheeting was also ancient.

I was required to install a radon mitigation system into the old house as it failed the radon test the buyers ordered. I paid the company that did the test.

When I look at the old bid document (which must be generic) it says:
- One 5" hole will be core drilled in the concrete floor. Approximately 8-10 gallons of substrate will be
removed to form a suction pit.
- 3” schedule 40 vent piping will exit from interior suction point and be mounted externally and vent pipe will discharge above the roof line
- A single continuous radon exhaust fan will be mounted externally (unless otherwise noted) and as close to ground level as possible.

They actually dug into the dirt in the raised crawlspace. I assume this was the "suction pit" and it was maybe gravel filled??

I am curious this particular installation method is something I can replicate for the current house. When I Googled I kept finding white plastic encapsulation solutions for crawlspaces.

We use the crawlspace to store items like plastic tubs full of Christmas decorations that are rarely need and it seems these encapsulation solutions are maybe designed for a crawlspace that remains empty.
 

Last edited by dorkshoei; 12-01-21 at 04:54 PM.
  #2  
Old 12-01-21, 04:34 PM
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It may depend on what was under the dirt when they dug.
I'd imagine they'd have to get down to rock and draw air thru the rocks to outside.
Doesn't sound terribly effective.

I would think that an HD plastic covering/tarp would be required.
Remediation in dirt video
 
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Old 12-01-21, 04:58 PM
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Doesn't sound terribly effective.

Right.

I can't remember if there was a re-test after it was installed. I don't think so. The company that did it is reputable.


I would think that an HD plastic covering/tarp would be required.
Remediation in dirt video

No encapsulation was installed.

 
  #4  
Old 12-02-21, 10:12 AM
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It all depends on how much radon is infiltrating and IMO, a lot depends on some "we'll try it and see if it works".

I agree this was not what they quoted and not what they should have done. The concrete slab acts as a decent form of encapsulation, so by drilling into that and pulling air from underneath, it should be pulling air from under the whole crawlspace area.
Additionally, they should have re-tested after it was complete to prove that it's below the EPA threshold. But ah well.

If you do it in your house, there should be some barrier. So either pull the air from under the slab, or add plastic over the dirt and pull from under that. Again, depending on how high the radon levels are, and what the test looks like afterwards, you may have to better seal or add additional "suction pits". My understanding is that you should be pulling air from each 'section' of the basement, based on where footers and such are installed that cut off different sections. In my old house, there are basically three separate basement "rooms" based on the way the house was renovated over the years. Each has its own foundation/footing, so the mitigation system was installed with 3 separate vent pipes pulling from each room.
 
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Old 12-02-21, 03:39 PM
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So here is the long version.

In the old house we sold the buyers radon inspection was "5.1 Pico curies per liter." over 48 hours. Since that was about the EPA 4.0 I had to pay for the mitigation.

As I said earlier, the bid document said:
- One 5" hole will be core drilled in the concrete floor. Approximately 8-10 gallons of substrate will be
removed to form a suction pit.
- 3” schedule 40 vent piping will exit from interior suction point and be mounted externally and vent pipe will discharge above the roof line
- A single continuous radon exhaust fan will be mounted externally (unless otherwise noted) and as close to ground level as possible.

They didn't however drill into the concrete floor. Instead they dug a pit (red arrow in attached picture from the bid) into the dirt of raised crawlspace. I don't have a picture nor do I know how deep they dug.

Then 3" tubing laid horizontally on the raised crawlspace out through a hole in the foundation to the fan and then vertically to above the roofline.

They did no new encapsulation but since the crawlspace was open I'm not sure how much that would help?

The bid says they would retest. I doubt the buyers would have accepted anything other than a retest but I don't have the post install result. I assume it was under 4.0 :-)

-------

The new house the radon test we had performed at movein (house unoccupied) was 3.2 pCi/L avg (4.4 max, 2.0 min).


It's the same kind of half basement and raised crawlspace (3ft above basement floor) but it's closed off with framing and drywall. Rest of basement is finished.

I just purchased a RadonEye home radon tester (https://www.amazon.com/dp/B01IH7SGCQ). Initially the results were very good but now they are not good. I inherited a cat and she died after 2 years, lung tumor and she spent all her time in the finished basement.

I'll schedule a professional radon test over a long period to see how accurate this Radon Eye tester is. Maybe I'll get a bid and see how different it was from the old install, which I'm confident I can do myself.

Thanks for the advice.

 

Last edited by dorkshoei; 12-02-21 at 04:37 PM.
 

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