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Radon mitigation in a combination basement/crawlspace

Radon mitigation in a combination basement/crawlspace


  #1  
Old 05-04-15, 06:32 AM
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Radon mitigation in a combination basement/crawlspace

Hello! I've got a combo basement-crawlspace, and I'm attempting to finish it out a little bit and also mitigate a slight radon issue (12 pCi/L).

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I want to finish the block walls up to about 6 feet. The challenges are bridging the gap between this wall and the dirt/rock with the membrane, and also making sure I can still access the crawlspace without damaging the membrane. I drew up this sketch.

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Does this look like a good solution? That 3" pipe is the pipe that will serve as the sub-membrane pipe, which will tie into an exterior fan.

Thanks. Any advice (radon-specific or otherwise) is very welcomed.


Ian
 
  #2  
Old 05-04-15, 07:12 AM
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Not a pto on Radon, but I think you will need to include the bottom slab into your vented area.

Is there a reason you want to use a block wall if it isn't going to be backfilled?

Bud
 
  #3  
Old 05-04-15, 07:27 AM
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Thanks, Bud.

I just bought the house and it already had the block walls a third to halfway done around the perimeter of the basement slab. You think it should be backfilled with stone no matter what?

For the slab itself, I figured I'd just seal any cracks in it.
 
  #4  
Old 05-04-15, 07:48 AM
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Not sure if that wall could take the back pressure of being backfilled, just thinking a floor to ceiling stud wall with a hatch entrance might be better. Probably too late. But I have not really considered the pros and cons.

If memory serves me, < 4 is your target for Radon and starting at 11 might require a more complete system. But retrofitting to that bottom slab will require some work. What you might do is design your system to evacuate the entire below slab area as best possible and include any pipes or plastic now before you close things up. Then test the partial system to see if you have reached an acceptable number or need to do more.

As for patching a radon system together, it needs to test good and meet the next home inspectors approval. New buyers may want the entire basement floor area included.

Bud
 
  #5  
Old 05-04-15, 08:35 AM
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Yea, I'd be worried about backfilling that wall, especially without a stud wall in front of it.

Another goal was to maintain easy visual and physical access to the entire crawlspace, which is why I'd leave open space all around the top of the block wall.

You're right, btw - 4pCi/L is the target amount per the EPA.

Good point on sub-slab suction. It'd be good to keep that as an optional "add-on" if covering/evacuating the area of the exposed dirt and rock still doesn't do the trick.

I'm gonna meet with a contractor who does this sort of thing.

Thanks!
 
  #6  
Old 05-04-15, 09:27 AM
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Is this a case that the previous owners decided to dig out a crawlspace and convert it to a basement?

Since your frost line is rather shallow, your footings are probably not very deep, thus the new block wall should have new footings and be strong enough to provide support to the ground under and inside the original footings.

If this is the case there should have been some engineering done and permits and inspections.

Bud
 
  #7  
Old 05-04-15, 09:42 AM
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Hmmm. I would hope that whatever footers exist are strong enough for a 6' block wall. But I'd have to look into it.
 
  #8  
Old 05-04-15, 10:54 AM
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Some of the more experienced contractors will be along, but if this is a conversion from a shallow crawl space to a deeper basement, then the new wall needs to be strong enough to retain the existing foundation wall and footings. That is where I suggested some engineering should have been involved.

Bud
 
 

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