DIY 'semi-encapsulation' - Vapor Barrier

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Old 12-18-18, 11:31 AM
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DIY 'semi-encapsulation' - Vapor Barrier

Hi. I own a 1970's brick ranch in SC, on a crawl space. When I bought the house, the crawl was a swamp. One of my first tasks, installing proper drainage, piping everything well away from the house. As expected, the crawl space was bone dry from that point on, however, the duct work and insulation in the crawl were ruined. After replacing the HVAC , duct work, and insulation, I decided to do a 'semi' encapsulation. I put down a good (not perfect, but good) vapor barrier, closed off all of the vents, and installed a good dehumidifier. I've since been pleased with the results. The crawl is clean, and bone dry...a pleasure to work in, when i have to.

Last spring, I happened to see that my county is 'zone 1' for radon. I bought a detector, in May, and my radon levels were below 1 most of the summer. Unfortunately, once the attic fan quit running regularly, my radon levels started creeping up. Since the AC is not running, i'm ventilating the crawl for about 7 hours a day...this helps, but my readings are frequently above 3 pCi/L, and can shoot up to 7 after a good rain.

I want to do whatever I can to protect my family, however, I can't afford the $15,000 or so a mitigation company would charge to fully encapsulate the crawl and install mitigation. I'm capable of correctly installing the plumbing and mitigation fan, but i'm not sure that my vapor barrier is air tight enough to allow the mitigation fan to work as intended. I have a total of 52 cinder block piers in the crawl, and the ones on the outside walls, are 2 to 3 inches off the brick veneer. Getting a good seal against the veneer wall will be nearly impossible (see attached photo).

Would sealing the vapor barrier at the perimeter, to the earth floor tightly with landscaping pins, be a reasonable option (of course, sealing all pins). Then, I could seal against the center piers in the correct way, and tape all holes and seams. I've read about sealing the edges with sand bags, or pea gravel, but considering I have 228 ft of perimeter wall, that is a daunting task. Bottom line, does the seal have to be 'perfect' for the mitigation fan to be effective?

Thanks.
 
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Old 01-20-19, 03:15 PM
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I know it's been over a month since your post, but I had to reply, mostly because of me being impressed with the encapsulation (or semi-encapsulation as you refer to it).

Since your radon levels aren't sky high, and it looks like you have a decent covering, I would try installing a fan and piping to pull the radon out from below the plastic and out of the house. You'll never get to 100% removal, but you probably wouldn't even get there if you did fully seal everything.

Do your best with some adhesive around the piers, to seal reasonably well, then I would dig a 1' round hole at one corner, and use that as your area to pull air from below the sheeting. Run that outside to a fan, then up over the roofline. Then test again. My guess is that you'd easily remove 75%+ of what you need to... bringing your levels down well below acceptable.

Would be curious to hear how it goes!
 
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Old 01-20-19, 05:38 PM
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There are two schools of thought on crawlspaces:
1. Insulate the ceiling, open the space to the outside air and seal it from the house air
2. Insulate the walls, open the space to the house air and seal it from the outside air

The first method is what's more common in your part of the country and it would be what you would have if you simply reopened the vents. This is what I would do.
 
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Old 01-21-19, 05:36 AM
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Thanks, Zorfdt...Stickshift. An update 1 month on. I'm still ventilating the crawl 7 hours a day...readings 2 to 3 when it's dry, spiking to 6 or 7 when it rains. Problem is, we've had a lot of rain down here in SC in recent weeks, so my readings have been 4+ consistently.

I've started the process of re-sealing all of my seams with poly encapsulation tape, and sealing against the piers. I'll be running 80 ft of perforated pipe under the poly, seal everything up, then run the pipe into the attic , exhausting through the roof with a mitigation fan. Like you said, Zorfdt...my levels aren't 'Blue Ridge Mountain high', but anything over 2 makes me uncomfortable. If I seal carefully, it can only help. I'm willing to part with $500 and 40 hours of crawling to find out.

Thanks for responding as well, Stickshift. As you can see from the photo on my first post, I've insulated the crawl well. The problem is the duct work. In the SC summers, when the warm humid air hits the air conditioned duct work, the condensation is pretty bad. When I had my duct work and HVAC replaced a few years ago, I was horrified at what we pulled out of the crawl. Much of the duct work was covered with black mold, inside and out (see attached photos). This is pretty typical down here when the duct work is in the crawl, it's just that 99% of folks never go into their crawl, so they just don't know (Yikes!). I wish my ducts were in the attic...I'd open my vents and be done with it. As it is, I need to keep the crawl as dry as possible.

Thanks again. I'll post again with the mitigation is up and running.
 
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Old 01-21-19, 02:53 PM
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All of that condensation tells me the ventilation down there was likely inadequate. Use of an exhaust fan in one of the vents to encourage air flow might be a good idea.
 
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Old 02-03-19, 07:24 AM
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If you open the crawl space vents what kind of humidity do you see down there during the rainy days and summer?
 
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Old 02-03-19, 10:50 AM
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Hi, missed your original post, glad it popped back up.
Are your radon reading from the crawl space or inside the house?
Converting your current vapor barrier to a traditional depressurized area below probably won't be successful, but with your low readings it probably doesn't need to be. Simply venting the air below the VB should reduce the reading without all of the perfect sealing and radon fans don't care they can work against a sealed cavity or just move some air.

I'll watch.

Bud
 
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Old 02-04-19, 04:54 PM
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Jeweler...i currently have an exhaust fan running at 900cfm at the rear of the house, and 4, 4 inch backdraft preventers spaced along the front of the house. Rainy days this winter, after running 7 hours, the humidity in the crawl is equal (or close to) the outside air. I haven't ventilated in the summer, and don't plan to. When the warm moist air hits the cold duct work, there will be condensation, which i'll avoid as all costs (see photos of old ducts in this thread).
 
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Old 02-04-19, 05:06 PM
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Hi, Bud. The readings are in the living space (beside me as I type). As mentioned before, I'm in the (slow, painful) process of sealing against the piers, and plugging all the holes i can in the vapor barrier. Instead of tacking the edges down with landscaping pins, i've decided to seal the edges with water bags used for holding down pool covers. Likely be quicker than hammering and sealing a few hundred landscape pins.

I think you are right about the mitigation. I doubt i'll ever get a perfect seal, but if i can get close, and get a good mitigation fan, I think I should be able to get my readings below 4 pCi/L consistently...shooting for <2. We'll see how it goes
 
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Old 02-05-19, 07:12 AM
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Dealing with high humidity and radon sounds difficult. We did the encapsulation for humidity which worked great. But no radon issues. We are close to the ocean and have humidity year around. No way we could bring in outside air in the summer unless we dried it first.
 
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