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Discussion Starter · #1 ·
i have tested for radon levels recently and the levels came back elevated. i am considering a mitigation system. now i have tested in past and radon levels were low so not sure if its seasonal or what bases it fluctuates on but
i am going to do another test. maybe out hrv wasnt running this time i tested.
anyways, our house is monolithic slab on grade. the slab is set on native soils which is quite sandy, the builder put layer of recycled concrete on top of that and rigid insulation just below slab. now what i am not sure is if the crushed concrete layer is air permeable. i cant find any info on that. will it let the air through when i install fan to suck the air out from below slab?
thanks
 

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I can't know the permeability of your crushed concrete base.....but I would think you have an excellent base for success of a radon mitigation system.

Even your ridgid foam provides channels for a radon mitigation.

And sandy soil is an advantage. along with a mono-pour.

I think you are an excellent example.



Where are you located....
 

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Radon mitigation is more about a negative pressure below the slab than air flow. By sealing all possible leaks (there will always be some left) the fan will create a negative pressure and prevent the radon gas from entering the basement. The base material you describe should be fine.

As for radon levels varying with the seasons I would think yes and higher readings in the winter when stack effect dominates the pressures in the house.

Be sure to seal any floor drains and the sump pit. I usually recommend a new sump pit be constructed for the pump and that be a sealed pit in case a pipe breaks.

Bud
 
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It should be sufficient. A simple smoke test or a more sophisticated pressure test would confirm that.

With an HRV, that is considered adequate by many. If you want to expel the radon prior to dispersing above the slab though, then some holes in the slab like you're thinking is the way to go.
 

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I didn't see where the op mentioned "holes in the slab" as part of the radon system. Anyway, all holes should be sealed to help the fan create that negative pressure and a u-tube manometer installed to be able to monitor that pressure.

Bud
 
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Discussion Starter · #7 ·
I didn't see where the op mentioned "holes in the slab" as part of the radon system. Anyway, all holes should be sealed to help the fan create that negative pressure and a u-tube manometer installed to be able to monitor that pressure.

Bud
yeah, i am not planing holes in the slab, i want to go through the side of foundation on the outside. (radiant tubing in slab and fairly open floor plan so not really a good options to locate pipes). i also have some 12" deep grade beams so i assume i will need to treat each section, so 3 pits.
i have sealed the holes that are exposed (in fact only holes are sewer pipes penetrations), rest of the plumbing penetrations are concealed in walls so i dont have access there, also concrete covered with flooring so cant seal any possible cracks.
 

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Discussion Starter · #9 ·
I'm not aware of any other way to suck air from below a slab besides having holes either through the top or in under the side. No mention of using an existing sump.
i actually want to drill holes from the side, form outside, just below the bottom of slab. but this might make the hole too deep to be able to make the pit? since it is monoslab and the foundation walls slope on the inside, it gets over 24" thick towards the top.
 

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Hard to find a link that addresses just slab penetrations but I stole a couple lines from this link.
"· Caulk or a permanent seal for cracks and seams in the slab and for all penetrations through the slab and the slab perimeter
· An airtight sump lid (if the basement has a sump)"

The soil around a house will almost never be perfectly air tight so depressurizing the sub-slab area will draw a slow air flow from below the slab into the radon fan. As the Op originally asked the soil below the slab needs to be air permeable, which sand or the crushed concrete he described should qualify.

Bottom line is all cracks and holes through the slab from the basement should be sealed.

Bud
 

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"holes in the slab" was referring to coring for the radon pipes, there can be more than 1 depending on SF. Gotta suck the air out from somewhere, don't know why some responses are disregarding this.

Anyway, sounds like OP has a handle on the thought process, the thickened slab presents a problem going in at the side. Also, with sandy soil the collection pocket can collapse, so better to be in the gravel. There's gotta be some places from the top you can core where there is no radiant, even if it's through the bottom plate of a wall. If the grade beams were poured with the slab, there could be enough gravel underneath them to get good communication from a farther access point.
 

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If you are going to test again, go for very long term if you can, test over weeks to months or even a full year measurement. Of course, if you are indicated very high in a short term test, you won't want to take the exposure risk. Short term, days, only exists so people can sell and buy homes. It is not a very good indication of what is really going with respect to individual risk and anyone that is conversant on the subject knows it.

Radon is dangerous so pay attention to it. Part of the problem is that as gaseous radon decays, radioactive solids are generated that are very small particles, smaller than any other dust that they will be aggregated with. The smallest particles are inhaled deeply into the lungs . (The smaller the particle the deeper it goes and tighter it sticks.) That means that your living space accumulates radioactive dust. Think about it. You have what is essentially in infinite source filling your home. It flows or diffuses in and does not leave very readily unless you have HEPA vacuum cleaners or outside exhausting vacuum cleaners and air exchange that would make you very uncomfortable, never mind impossibly expensive.

The preceding radioactive decay in the series is solid, and chemically inert radon 222 has a half life of nearly 4 h. This makes it easy for it to work its way loose from the soil into your home pretty efficiently. After that, a few very short half life (minutes to seconds) unstable elements lead to a, key to us, Pb (lead) 210 to a bismuth 210 decay that has a half-life of 22 years. Look at it like scattering pea gravel into a pond. The radioactive dust that your lungs don't filter out just accumulates.

I might agree about the asbestos risk and if you stay away from it (keep it intact) or handle it with relatively simple precautions, the risk approaches zero if there was any to start with. If you don't attack it, it can't hurt you. Radon on the other hand, is an agressor.
 
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