[Joe trio]

Take a look at these pics of a gravel crawl space.
Previous VB was put down terribly, not overlapped or sealed.
We tore it up and put down 6mil poly and sealed it to the walls, overlapped and sealed seams.
Now it's blown up like a balloon!

Ever seen anything like this? Can't beleive the pressure differential would be great enough to cause this. House has massive radon problems, levels at 15 pCi/L WITH installed mitigation unit.

-Joe

 

[Trim40]

Earthworm flatulence?

 

[AustinDB]

good job on the VB installation

there is a spec on the DOE website for a PVC vent pipe to take the radon gas out of the crawlspace-the pipe vents off the gas to above the roofline to keep everyone healthy.

were you wearing masks during the install?

 

[Cletus]

Does the mitigation unit have a fan? Maybe it is blowing the wrong direction.

 

[Joe trio]

good job on the VB installation

there is a spec on the DOE website for a PVC vent pipe to take the radon gas out of the crawlspace-the pipe vents off the gas to above the roofline to keep everyone healthy.

were you wearing masks during the install?

Thanks. Yes, we did bury a 25' length of this drain pipe and "T" connect it to a stub pvc vent to possibly connect it to the mitigation unit, or a second one. looks like we might have to. Can't see it in the pics because the VB is puffed up around the pipe.

Does the mitigation unit have a fan? Maybe it is blowing the wrong direction.

Yes, mitigation unit has a fan. It depressurizes at 1.5 to 2.0 in-H2O. It blows out.

Here's a pic of the drain tile we installed

 

[AustinDB]

are you saying you HAVE this in place (VB instead of concrete) and still getting the air pocket? might have to put pea gravel ontop of the plastic to keep it down. What if had put down gravel first, then the plastic, which might allow the gas to find its way to the piping out of the space. note: not sure if it would work

 

[Chris G]

I have no idea what's going on, but I would just let it keep going like that. Then put a big flat screen on the wall, smoke an enormous joint, and recline into the biggest baddest inflatable chair in the universe.

 

[cexcavation]

My guess is that you did such a great job sealing the vapor barrier, the heat from the ground is trying to balance the temperature of the crawl space and can't escape. If the ground is emitting 50deg and outside temp it 30deg. warmer air is going to rise and get trapped.

The only solution I see is as described previously-add pea gravel over the entire area to hold the barrier down. Surface area to surface area, your perf. pipe is not going to be able to exhaust the volume of air fast enough to hold it down.

One way to test my theory is to get a job heater or two and warm up the crawl space. If the barrier goes down, you know your answer. If it stays up, then pipe out whatever is under there and see if it burns-you may be sitting on a natural gas well!!!!:laughing:

 

[Joe trio]

are you saying you HAVE this in place (VB instead of concrete) and still getting the air pocket? might have to put pea gravel ontop of the plastic to keep it down. What if had put down gravel first, then the plastic, which might allow the gas to find its way to the piping out of the space. note: not sure if it would work

Thanks for the reply chevy. A little more clarification on my part, I apologize. We have that on the basement side but not the crawl side.
The foundation is 1/2 basement, 1/2 crawl. Basement side (concrete obveously) has the mitigation unit. The crawl side has black drain pipe under the pastic, burried in pea gravel, ready to hook up to the mitigation unit or a secondary unit, but capped currently.
Under the VB is pea gravel and then dirt below that.

The basement has two sump pits, yes two, both in the basement area. First one connects to the outer perimeter drain tile, second one connects to the inner perimeter drain tile. The mitigation unit is hooked up thru the second (inner) one. The first pit is sealed.

I think hooking up the crawl pipe to the mitigation unit is what I need to do. I just have never seen this and was wondering if anyone else has.

 

[Joe trio]

My guess is that you did such a great job sealing the vapor barrier, the heat from the ground is trying to balance the temperature of the crawl space and can't escape. If the ground is emitting 50deg and outside temp it 30deg. warmer air is going to rise and get trapped.

The only solution I see is as described previously-add pea gravel over the entire area to hold the barrier down. Surface area to surface area, your perf. pipe is not going to be able to exhaust the volume of air fast enough to hold it down.

One way to test my theory is to get a job heater or two and warm up the crawl space. If the barrier goes down, you know your answer. If it stays up, then pipe out whatever is under there and see if it burns-you may be sitting on a natural gas well!!!!:laughing:

Crawl's about 65 deg. Outside (Ohio) is 30. I think you're right. If you think about it technically, under the VB is connected thru to the outside. Above the VB in 'inside' air at inside pressure and temp. Negative pressure inside the house + warmer than outside = differential.

Kicker is even with the crawl well sealed AND a mitigation unit installed, radon levels are still at 15pCi/L.:blink:

 

[Calvinmurphy]

Crawl Space Plastic

Extending the mitigation existing mitigation system to the pipe that was placed under the plastic in the crawl space will pull the air out from under the plastic and the plastic should be pulled down tight. If it is not pulled town tight, this indicates that the volume of air coming in under the plastic is greater that the capacity of the fan. In most cases, the plastic will be pulled down tight. Since the crawl space was not treated as part of the mitigation system installation, you should expect the radon level to be reduced as well. I would suggest that you conduct another radon test a couple of days after extending the system to under the crawl space plastic. In most cases, it is not necessary to add a second system. Just run piping from the existing system to under the plastic in the crawl space.

Having the plastic billow up in crawl spaces that do not have the mitigation system extended to beneath the plastic barrier is very common in the winter. You just need to be sure that the plastic is secured to the walls and that the seams are sealed in a permanent manner. If the plastic comes loose from the walls after you have applied suction beneath the plastic, you are going to lose conditioned air from inside the house.

 

[Michaeljp86]

If I had radon that high Id want a fan on the pipe under there. That should pull the plastic down. Id throw some gravel on there too. I just did a radon test here, its 1.8.

 

[AustinDB]

Kicker is even with the crawl well sealed AND a mitigation unit installed, radon levels are still at 15pCi/L.:blink:

are you saying that the crawlspace does have a pipe heading outside? seems I understand it's not, in which case the built up radon has to go somewhere-it's only going to push the VB bubble so far before it finds a path of least resistance-through the soil, pours in the block wall or somewhere else. doesn't seem moisture is the issue, in which case the space needs a pipe heading above the roofline to get the radon out.

let us know what it takes to finally get the level down.

 

[Joe trio]

are you saying that the crawlspace does have a pipe heading outside? seems I understand it's not, in which case the built up radon has to go somewhere-it's only going to push the VB bubble so far before it finds a path of least resistance-through the soil, pours in the block wall or somewhere else. doesn't seem moisture is the issue, in which case the space needs a pipe heading above the roofline to get the radon out.

let us know what it takes to finally get the level down.

The crawl is just piping under the plastic, then a riser capped off for right now. The mitigation unit is in the basement side of the home. The crawl isn't connected to the mitigation unit, yet. We put piping under the VB when we laid it just incase we needed to mitigate the crawl, we didn't have to tear up the VB again.

pic

 

[Joe trio]

Extending the mitigation existing mitigation system to the pipe that was placed under the plastic in the crawl space will pull the air out from under the plastic and the plastic should be pulled down tight...

Thanks Calvin. Third pic is of the mitigation setup, installed by my radon guy.
We also caulked the seams between the basement slab and wall (pic 1).
Second pic is a cross section of the foundation. The water table is high, right below the formadrain, and is controlled by the formadrain/sump system. AKA if pumping goes out, basement floods about 1 ft. Volume of water depends on rainfall and seasonal water table levels.

My radon guy claims that the high water table is thwarting the mitigation unit. I claim that the drain system is taking the water below the gravel that's under the slab thus the unit should still depressurize the sub slab.

I'd be interested to see what you think.

 

[Calvinmurphy]

I'm glad to see that the wall/floor joint was caulked. That will minimize loss of heated and conditioned air from inside the house and improve system performance. Is the water level in the sump pit above the sump pit drain tile? According to your drawing, the water level is below the drain tile. If the water level is consistantly above the drain tile, the mitigator is correct. Can the sump switch be adjusted to lower the water level? Has the mitigator conducted what we call pressure field extension or comminication tests to see if there is suction beneath the slab? This is accompolished by drilling a .5 inch hole through the slab a distance away from the suction point - sump pit- and using either smoke or a micromanometer to measure the pressure differential above and below the slab. If the smoke goes down the hole or the micromanometer shows negative presssure, you have suction under the slab and the radon is coming into the house from another entry point.

 

[doubleaction]

I know on a few jobs i did like that the inspectors wanted pea gravel on top of the VB. Never questioned the reasoning though.

 

[Joe trio]

Is the water level in the sump pit above the sump pit drain tile? According to your drawing, the water level is below the drain tile. If the water level is consistantly above the drain tile, the mitigator is correct. Can the sump switch be adjusted to lower the water level? Has the mitigator conducted what we call pressure field extension or comminication tests to see if there is suction beneath the slab? This is accompolished by drilling a .5 inch hole through the slab a distance away from the suction point - sump pit- and using either smoke or a micromanometer to measure the pressure differential above and below the slab. If the smoke goes down the hole or the micromanometer shows negative presssure, you have suction under the slab and the radon is coming into the house from another entry point.

Thanks Calvin. The water level is approx even with the bottom of the drain tile. There are no holes in the sump pit to allow water thru the pit walls. When the water level raises, it is channeled thru the drain tile and into the pit. This is often the case as the sumps kick on approx every 20 min.
The pump is lower than the drain tile inlet to the pit, so the water table can't be lowered by simply moving it down more. Some ways to lower the water table are, 1) drill holes in the pits allowing ground water in 2) add a lower drain tile system 3) install external dry well below the drain tile to intercept the water and hydraulic pressure.

Good advice. I will call on my mitigator to perform these tests to ensure proper suction under the slab.

 

[Calvinmurphy]

If the water level is even with the bottom of the drain tile, you should have suction under the slab. I would check pressure field extension to be sure and get the system extended over to the crawl. If these actions don't solve the radon issue, there are other things that can be checked.

 

[Joe trio]

If the water level is even with the bottom of the drain tile, you should have suction under the slab. I would check pressure field extension to be sure and get the system extended over to the crawl. If these actions don't solve the radon issue, there are other things that can be checked.

That's good to know. Unfortunately, there's not a lot of information out there on what happens if the mitigation fails to bring down the levels. Apparently they're a reliable fix for high radon levels, not in this case!

My radon contractor is balking at doing any more work :furious:. He says the unit is in and functioning properly. Still blames it on the water.