[Options for installing a Radon mitigation system]

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mswin
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[Options for installing a Radon mitigation system]

Post by mswin » Sun Jul 22, 2018 12:15 pm

[Moved into a stand-alone post from: Radon --admin LadyGeek]

Have a new question but don't see where to start one. It is Radon related so started here.

We are interviewing companies for radon mitigation of our home which measured over 9 in the basement on a home test. We have a single story, no sump pump in the mostly finished basement with approx. 12x15 ft open dirt crawlspace next to the garage.

Question: We want to do the pipe entry into the slab, but not the crawlspace yet. We will leave a 'T' for future if the number does not go way down. One certified installer suggested to put one SSD in the room next to the crawlspace (but on the inside wall) and then had an idea to go accross the room drop a 'T' down the wall that is against the crawl space and then through the outside wall (which is open block) and into the dirt of the crawlspace, about a foot off the floor. Then suction would be about 4 ft below the dirt. So sucking radon from below the open crawlspace. So we'll have two suction points, one in the floor SSD, then through the wall to the dirt below open crawlspace. Then venting out the attic like normal.

What do you think? Have you ever heard that option? Would it actually draw the radon down and out the pipe? Any concerns with block wall. It is not sub wall suction as it would be in the dirt - but would it work?

We will do the encapsulation of the crawlspace if necessary - but it would be a huge job as it already has plastic down (though not taped) and a full floating floor as a storage area and is completely full.

Any thoughts on a pipe sucking below the open crawlspace?

IowaFarmBoy
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Re: [Options for installing a Radon mitigation system]

Post by IowaFarmBoy » Sun Jul 22, 2018 8:32 pm

So if I understand correctly, you will be pulling air/radon from 4' under the slab in the crawlspace? I think it is going to depend a lot on what your soil is like. I think the reason most sub slab depressurizaton (SSD) works is because there is commonly a layer of gravel or sand right below the basement slab so there can be some airflow. If you have 4' of a very sandy soil, it might work. It you are in clay, I can't imagine it helping much.

We had minor radon issues when we bought our house- just over the limit. I installed my own system and first just hooked up to the sump system. It didn't help a lot. We have a crawl space with dirt floor so I also sealed the floors and wall with a membrane and put a perforated pipe under the membrane on the floor that hooked into our fan and it dropped our numbers way down. I was surprised we had that much radon coming into the basement from the crawl space since there was a solid block wall between them with one window that allowed access to the crawlspace.

LMBFlorida
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Re: [Options for installing a Radon mitigation system]

Post by LMBFlorida » Sun Jul 22, 2018 9:23 pm

I can't imagine the below slab vent bringing the overall values down if the crawl space area is left open. If you placed some type of barrier over the soil in the crawl space and evacuated the air from under the barrier it may bring the overall values down. Our current home had raised levels found during the home inspection and the previous owner installed a SSD system below the slab on the lower level. It has worked as planned and values are now well below the allowable.

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queso
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Re: [Options for installing a Radon mitigation system]

Post by queso » Mon Jul 23, 2018 9:46 am

IowaFarmBoy wrote:
Sun Jul 22, 2018 8:32 pm
So if I understand correctly, you will be pulling air/radon from 4' under the slab in the crawlspace? I think it is going to depend a lot on what your soil is like. I think the reason most sub slab depressurizaton (SSD) works is because there is commonly a layer of gravel or sand right below the basement slab so there can be some airflow. If you have 4' of a very sandy soil, it might work. It you are in clay, I can't imagine it helping much.

We had minor radon issues when we bought our house- just over the limit. I installed my own system and first just hooked up to the sump system. It didn't help a lot. We have a crawl space with dirt floor so I also sealed the floors and wall with a membrane and put a perforated pipe under the membrane on the floor that hooked into our fan and it dropped our numbers way down. I was surprised we had that much radon coming into the basement from the crawl space since there was a solid block wall between them with one window that allowed access to the crawlspace.
I am thinking about DIYing this after looking at what's involved, but can't get my head around one aspect of it. How did you figure out where to punch the hole in the slab and how critical is the placement of said hole in relation to the rest of the slab/house? Does it need to be more central or can it be close to a corner? I'd really only like to have to punch the hole once so figuring out where to put it is giving me pause. Thanks!

EDIT - just reread your post and it sounds like you did a perforated pipe under your vapor barrier and that got your levels down without having to do the slab. If that's the case, I am definitely going to try what you tried first in case my radon levels are primarily coming from my crawl space. Our homes sound similar (finished basement on slab adjacent to encapsulated crawlspace separated by a block wall). Thanks!

mswin - our home sounds similar to yours, but your levels are much higher than ours (I have had short term peaks of 4.2, but my long term average is around 2 or so). I have 1/3 finished basement, 1/3 garage (slab) and 1/3 encapsulated crawlspace (vapor barrier over dirt and gravel). I am thinking about punching into the slab in my utility room for the slab and then linking that up with another PVC run that comes from under the vapor barrier in my crawlspace and then teeing them together, going through the foundation wall and then outside to a single fan and vent pipe that ends above the roofline. I'm still in the "thinking about it" phase, but I don't like any of my local contractor options so I may either do nothing or do it myself. I'd love to hire it out, but when I talk to a tradesman I like to come away impressed with his/her knowledge level and feeling comfortable they are going to do a better job than I am. I didn't get that feeling with the guys I talked to.

mswin
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Re: [Options for installing a Radon mitigation system]

Post by mswin » Mon Jul 23, 2018 6:16 pm

Thanks for all your replies. Just to clarify we have not done anything yet for the radon. We have a 4 or 6 mil plastic laid on the dirt floor only because we were putting in a floating wood floor for storage (we have no cement slab in the crawlspace). So currently have no real encapsulation in the crawlspace or any sub floor hole in the room adjacent.

So the radon company is proposing one entry on the opposite wall in this room, which is next to the crawlspace so it is more central in the basement (the room isn't a bedroom so placement isn't an issue)- so pulling more from the center of the house. He would then go through the rafter and then drop down a pipe just before entering the crawlspace. He would then create an elbow and drill through the block wall to the dirt in the crawl space. Thus pulling radon from the dirt before it goes up. Don't know if it is better to be far down or near the top of the dirt floor. Maybe he was thinking he would be closer to the slab and thus suck from both areas. Don't really know if has ever done this before. Good question to ask.

I really don't know if this would work that is why I am seeking advise. I don't know our soil type other then it isn't sandy and I don't think it is clay. We could dig a small pit for the air, but wouldn't think it could be very big as the dirt/weight above it.

The other company is proposing the sub floor hole be in the furthest corner next to the crawlspace.

Both are putting in a 'T' in the crawlspace incase we need to go the full encapsulation if numbers don't go down.

IowaFarmBoy
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Re: [Options for installing a Radon mitigation system]

Post by IowaFarmBoy » Tue Jul 24, 2018 4:51 am

queso wrote:
Mon Jul 23, 2018 9:46 am
I am thinking about DIYing this after looking at what's involved, but can't get my head around one aspect of it. How did you figure out where to punch the hole in the slab and how critical is the placement of said hole in relation to the rest of the slab/house? Does it need to be more central or can it be close to a corner? I'd really only like to have to punch the hole once so figuring out where to put it is giving me pause. Thanks!

EDIT - just reread your post and it sounds like you did a perforated pipe under your vapor barrier and that got your levels down without having to do the slab. If that's the case, I am definitely going to try what you tried first in case my radon levels are primarily coming from my crawl space. Our homes sound similar (finished basement on slab adjacent to encapsulated crawlspace separated by a block wall). Thanks!
To clarify, I didn't punch a hole in the slab for the main basement, I sealed off the sump hole and went into the enclosure I built to seal off the sump. Most retrofits in our area seem to tie into the sump system.

In the crawlspace, I followed a procedure I found on line. I used some type of special membrane that I ran up to the top of the block walls and it glued to the walls with some kind of adhesive in a tube. The membrane was fairly thick and a lot tougher than just plastic which is good since I had to crawl on top of it to install it. Our walls are about 4' tall in the crawlspace. The membrane ran from one side to the other and I did something to seal the overlapping joints- like tape or more of the adhesive so the entire dirt and wall area was sealed off beneath or behind the relatively air tight membrane. Under the membrane on the dirt floor, I had placed a piece of 4" perforated pvc that was pretty long- like maybe 10' of the 20' width and this was attached to the radon fan. When I found this approach, it seemed to be professional and it makes sense in that it really seals off the area and creates a suction under the membrane. One the overall things you want to do is to have a system that is tight so that it creates suction in contact with the soil to pull out the gas. We have a manometer hooked up to our main pipe from the fan so we can monitor the vacuum being created and see if a problem has developed.

Sorry I am fuzzy on brands or details. It's been probably 15 years since I did this.

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queso
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Re: [Options for installing a Radon mitigation system]

Post by queso » Tue Jul 24, 2018 7:37 am

IowaFarmBoy wrote:
Tue Jul 24, 2018 4:51 am
queso wrote:
Mon Jul 23, 2018 9:46 am
I am thinking about DIYing this after looking at what's involved, but can't get my head around one aspect of it. How did you figure out where to punch the hole in the slab and how critical is the placement of said hole in relation to the rest of the slab/house? Does it need to be more central or can it be close to a corner? I'd really only like to have to punch the hole once so figuring out where to put it is giving me pause. Thanks!

EDIT - just reread your post and it sounds like you did a perforated pipe under your vapor barrier and that got your levels down without having to do the slab. If that's the case, I am definitely going to try what you tried first in case my radon levels are primarily coming from my crawl space. Our homes sound similar (finished basement on slab adjacent to encapsulated crawlspace separated by a block wall). Thanks!
To clarify, I didn't punch a hole in the slab for the main basement, I sealed off the sump hole and went into the enclosure I built to seal off the sump. Most retrofits in our area seem to tie into the sump system.

In the crawlspace, I followed a procedure I found on line. I used some type of special membrane that I ran up to the top of the block walls and it glued to the walls with some kind of adhesive in a tube. The membrane was fairly thick and a lot tougher than just plastic which is good since I had to crawl on top of it to install it. Our walls are about 4' tall in the crawlspace. The membrane ran from one side to the other and I did something to seal the overlapping joints- like tape or more of the adhesive so the entire dirt and wall area was sealed off beneath or behind the relatively air tight membrane. Under the membrane on the dirt floor, I had placed a piece of 4" perforated pvc that was pretty long- like maybe 10' of the 20' width and this was attached to the radon fan. When I found this approach, it seemed to be professional and it makes sense in that it really seals off the area and creates a suction under the membrane. One the overall things you want to do is to have a system that is tight so that it creates suction in contact with the soil to pull out the gas. We have a manometer hooked up to our main pipe from the fan so we can monitor the vacuum being created and see if a problem has developed.

Sorry I am fuzzy on brands or details. It's been probably 15 years since I did this.
Thanks! This is exactly what I am thinking of doing before touching the slab. I already have an encapsulated crawl space with a vapor barrier so it should be relatively easy for me to throw a perforated pipe under the plastic, elbow that up to some PVC and then attach an inline fan and exhaust it out the side of my foundation through an existing foundation vent. I'm going to rig it up as a proof of concept for now with no PVC glue and a temporary exhaust setup just so I can see what effect it has on the level in the finished basement on the other side of the block wall. If after a week or three it drops the level quite a bit I'll go back into the crawlspace and make it more permanent and come up with a better way to exhaust it. Honestly, I'm thinking that dumping it out of an existing foundation vent under a deck is a pretty nifty solution. I'm not convinced it really has to be vented above the roofline, but I'll keep reading before making up my mind.

mswin
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Re: [Options for installing a Radon mitigation system]

Post by mswin » Tue Jul 24, 2018 8:41 am

We thought about venting out the crawlspace as well. A DIY person said if you have kids and they play in the area they would not recommend it as it releases the gas 24/7. Ours would go out to the back yard. Plus we get alot of snow so would have to be pretty high and we can't have the fan outside. Then there is if it is near a window and goes right back in the house. Best is out the roof, but some house layouts make it near impossible to do it inside.

I think we are leaning towards on sub floor suction point, "t" in the crawlspace and test to see if we need to do full encapsulation. Paying for a second pipe into lower wall of the crawl space is a big question for the money. If we put the pipe higher in the wall to get closer to the released gas then we might start loosing heat/air conditioning from the house and up the bills. Our luck we would just have to do the crawlspace anyways. Sure wish I knew if it would make a difference in the reading.

chambers136
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Re: [Options for installing a Radon mitigation system]

Post by chambers136 » Tue Jul 24, 2018 8:53 am

“perforated pipe under your vapor barrier and that got your levels down without having to do the slab”

This is what I did and it brought the levels down to what you would see in outdoor air. Just get some good thick vapor barrier. There are places online that sell materials specifically for this

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queso
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Re: [Options for installing a Radon mitigation system]

Post by queso » Tue Jul 24, 2018 8:55 am

mswin wrote:
Tue Jul 24, 2018 8:41 am
We thought about venting out the crawlspace as well. A DIY person said if you have kids and they play in the area they would not recommend it as it releases the gas 24/7. Ours would go out to the back yard. Plus we get alot of snow so would have to be pretty high and we can't have the fan outside. Then there is if it is near a window and goes right back in the house. Best is out the roof, but some house layouts make it near impossible to do it inside.

I think we are leaning towards on sub floor suction point, "t" in the crawlspace and test to see if we need to do full encapsulation. Paying for a second pipe into lower wall of the crawl space is a big question for the money. If we put the pipe higher in the wall to get closer to the released gas then we might start loosing heat/air conditioning from the house and up the bills. Our luck we would just have to do the crawlspace anyways. Sure wish I knew if it would make a difference in the reading.
That makes sense. I have some existing crawlspace vents that were sealed off when the crawlspace was encapsulated (the old rectangular screen type). I think I may make an adapter so I can vent out the existing hole/screen (prob just some plywood and foam insulation board with a 4" hole for my PVC). If I can use the vent I am thinking about, it exhausts underneath my front deck which is protected from snow and is near windows that are never opened. I think I am going to put the fan inline with the PVC under the crawlspace so I don't have to locate the fan outside. If I end up thinking venting under the deck is a bad idea I can just extend the PVC under the deck and out the side of the lattice and then run it to the roofline. My plan so far is to install a 10-20' perforated pipe under my vapor barrier and then attach it to a PVC elbow and run 4" PVC through a hole in the vapor barrier. That will run up near the floor joists and then hit another 90 degree elbow and head toward the foundation wall. I'll cut it there, install an inline fan and then extend the PVC after the fan to the existing foundation vent hole where it will mate to a 4" hole in foam board insulation and plywood that will be installed in the foundation vent hole against the screen (and spray foamed in place). As part of this, I am thinking about redoing my vapor barrier with this burly 20 mil stuff I found from a place that specializes in crawlspace encapsulation since the 6 mil stuff I have in place is probably 15-20 years old and needs to be repaired in a couple of places. To keep it easy I'll probably just go right over the top of the existing vapor barrier with the new stuff.

mswin
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Re: [Options for installing a Radon mitigation system]

Post by mswin » Wed Jul 25, 2018 8:47 am

I think it would be good to go over the old plastic. That's one more layer not to get torn by debris in the dirt. Mold can form between the two layers but not if you are doing a fan so the moisture is pulled out of the place. We will definitely make the plastic thick because we plan to put stuff back in there and we enter the room for seasonal storage.

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queso
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Re: [Options for installing a Radon mitigation system]

Post by queso » Wed Jul 25, 2018 8:56 am

mswin wrote:
Wed Jul 25, 2018 8:47 am
I think it would be good to go over the old plastic. That's one more layer not to get torn by debris in the dirt. Mold can form between the two layers but not if you are doing a fan so the moisture is pulled out of the place. We will definitely make the plastic thick because we plan to put stuff back in there and we enter the room for seasonal storage.
That's my current plan. I also have a commercial dehumidifier in there plumbed up to a drain so the humidity never gets above 50% or so anyway. I'm still working on the design of the system, which fan to use and the attachment system at the moment. What are you going to use for attachment? A lot of the videos and websites I have looked at are recommending Christmas tree fasteners every 18-24" driven through two sided butyl tape. From the looks of my existing vapor barrier, it was installed with a Hilti concrete fastener system (or similar) and then just taped to the wall above the fasteners. I sure like the idea of an air/electric fastener system better than I like the idea of crawling around and hammer drilling 1/4" holes in the block every 18-24", but I haven't made up my mind yet which way to go and haven't priced out what a fancy fastener system would cost or how much time it would save. I'm also torn on the vapor barrier selection. What I have looks like standard 6 mil plastic, but they make much nicer (and more $$) 10-20 mil reinforced stuff that would probably be more durable for when I am climbing around under there working on plumbing issues. I don't use it for storage so it might be overkill. Occasionally rolling around in there with shoes off hasn't torn the existing barrier so I am probably overthinking it. I also think the thicker reinforced stuff will probably be a lot harder to work with so there's that as well. :happy

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