remediating radon in new house, combine with finishing out basement

[RustyShackleford]

Just bought a vacation in the mountains, and inspection shows radon problem (averaged 7.4 pCi/l during short term radon test, the EPA action level is 4.0 pCi/l). The place has a semi-finished basement, so I'm thinking maybe I can kill two (or perhaps three) birds with one stone here. Here's my plan ...

This basement is full-height, and has a rough plywood floor (not securely fastened down, thin plywood), along with open-to-framing walls and ceiling. The handyman who's worked on the place THINKS there is 2x8 treated joists under the plywood. So I'm thinking to pull up the plywood, install a vapor barrier, put a vent system in (an exhaust fan and an intake) to ventilate the space between grade and the joists. Then re-install the floor, perhaps with thicker or better-fastened plywood.

Seems like this well get me part of the way towards finishing out the space for a rec-room or the like, drywalling the walls and ceiling in the future. I hope the ventilation of the under-floor volume will lick the radon. The third "bird", maybe put 2" rigid foam on the walls so it becomes like an encapsulated crawlspace.

Thoughts ? I wonder if vapor barrier should go on the soil, or just beneath the floor ? Seems like it'd be nice not to have the treated joists exposed to living space.

 

[peakbagger]

Boy you like your challenges I would take Radon over that electrical project!. In the radon reduction systems I have seen the vapor barrier/radon barrier goes as close to the living space as you can get it. On concrete foundations they put a layer for crushed rock down on the ground (many suggest putting it on geotextile) then the layer of heavy plastic is put on the crushed rock before the floor is poured. Concrete guys do not like pouring on plastic as it takes longer to float it so make sure they do not poke a fee drainage holes. The vapor barrier has to be sealed as tightly as possible. Radon is not just coming up through the floor it can come through the walls so you need to seal the walls. Ultimately you need air flow and a pressure differential between the space underneath and the living space above. If the floor and wall are leaky, its going to take a major effort to maintain the differential and more fan horsepower and long term power consumption. Some folks have tried to run the fans off of solar intermittently but everything I have read is 24/7 is far better.

BTW Radon frequently comes in with drilled wells and then pools in low points in the house. Putting in ventilation will eventually deal with the water born radon but far better to take it out where it comes into the house so you arent breathing it in when it comes out of the shower heads and sinks. That can mean an air stripper and blower on the well water plus a re-pressurization pump or in some cases a double carbon filter with a prefilter. Caron filter need replacement every so often but adding a air stripper and re-pressurization pump is steep up front and requires ongoing horsepower.

Be aware that Radon mitigation is a high markup field, some manufacturers may only sell to "qualified" contractors so it pays to shop. Its not rocket science, venting is just HVAC with thin wall PVC. I have seen Dwyer gauges that Hearth.com members may use for stack draft sold at 100% markup for Radon, the only difference was some intermediary put a sticker over the Dwyer logo.

 

[RustyShackleford]

Thanks for the response. Yeah, this should be easier than that electrical mess. But hey, I'm retired - need something to keep me off the streets.

One clarification (can't edit OP now): It's not a full basement, more like what I believe is called a "day basement". The house is built on a STEEP slope. So one side of the basement is more or less above grade, and the other side is underground. The full-height basement peters out into a crawlspace towards the buried part.

No doubt the mitigation is a money-teat for many contractors, which I hope to avoid. We discovered this during the "due diligence" period and sellers agreed to pay for the radon mitigation and fix the vapor barrier that's not in good shape where the basement peters out into a crawlspace. If it's not done by closing, they'll deduct the estimate from our closing costs (for some reason, that is considered preferable to deducting it from the purchase price - doesn't require modifying the contract, I suppose). Of course, I prefer the latter (give me the cash), and hopefully we can swing that. Hopefully I won't get into crazy price markups, since, as you say, it's ordinary stuff - fans, ducts, plastic sheeting.

Anyhow, back to the chase ... Sounds like I should pull first up the plywood. Then install two ducts to the outside, through the foundation wall below floor level. A fan which sucks out of the sub-floor space - thus creating slight negative pressure there - and an opening for makeup. Variable speed fan so I can trade-off electricity consumption versus radon mitigation. Then a vapor barrier on top of the floor joists and then put the plywood (or better plywood) back.

Well water is not an issue - we're on town water. But sounds like I could get some radon in through the walls which are below grade. Seems like I'd want to seal those walls good, for moisture, anyhow; seems like that would handle the radon. Given I'm not quite 2X the standard, I imagine simply blocking the radon from below would do the trick though.

 

[peakbagger]

I figured it was not a standard basement. I am unsure about needing an air inlet, yes you want air flow but you also want pressure differential to pull the radon out of the soil. My guess is no matter how tight you make things there is always going to be leaks which create air flow. My guess is install an air inlet in an opposite corner away from the air inlets but have a good way of throttling it. You want enough flow to sweep the gas to the outlet but excess flow will use more horsepower. Then again if the soil is potentially damp, you may want to run it at a higher flow to get it out of the basement.

I sold my parents house several years ago (pre latest real estate boom), it was nice 1960s house and the offer was for over the asking price from several buyers. I picked one and she made the offer contingent on inspection. The inspector came back with Radon as an issue which is typical of southern Maine as the aggregate used for the concrete contains Radon. I agreed to a flat $2,500 reduction with the agreement that the house was as is where is (in legal language). There was some potentially expensive, but disclosed issues that could have been for more expensive to deal with in the future that the inspector did not flag so the $2,500 reduction was worth it to get the as is where is language included.

These days in a crazy market there are a lot of stories of folks buying major defects in homes by waiving inspection and accepting as is where is type clauses. I have seen some stories of homes with major mold issues making the house unlivable that new owners got stuck with due to buying without inspection. The end up with a unlivable home and big payments.

 

[RustyShackleford]

Interesting story.

So, sounds like you agree with my plan to install venting below the floor and vapor barrier between floor joists and plywood. The only question is how much inlet air, and how high to run the fan.

Just read that radon is the densest naturally-occurring gas, about 8X the density of air. I'm surprised this is even a problem, except it low areas, like basements, where it can collect.

 

[peakbagger]

You have figured out the deceit with radon . Unless someone lives in the basement, the radon levels in the living space of the house typically tests far lower. Radon tends to "puddle" on the floor and on low points. Typical testing is done at the floor or the low point. The far bigger impact is radon coming out of solution from showers and aerators from Radon in the water. It bubbles off easier the hotter the water.

I know of one person with high levels of radon in the basement that just vented the barometric damper on the oil boiler down to a low point on the floor. The stack was always pulling air up the stack and that was enough flow to vent the radon.

My guess is fan flows are set by rule of thumb with testing to confirm.

 

[RustyShackleford]

I'm thinking it's worth investing in a meter, like this. Pay for a few one-time tests, allow me to compare basement with higher levels, and give some peace of mind (when planning to do work in basement).


Amazon product ASIN B00H2VOSP8

 

[RustyShackleford]

Another question: I bought the meter (that I linked above) and tried it out in the crawlspace of my own house (not the vacation house of my OP). The level was about 5 pCi/L, above the EPA standard. But this was my crawlspace - I don't tend to hang out there So I've tried it in several rooms of the house itself, and readings are about 1 pCi/L. Should I be worried ?

I suspect if the vacation home were checked in areas above the basement (where the inspector checked it) that it would be in the safe range too. But I hope to finish that out to be a rec room or something, so it's still unacceptable.

 

[EbS-P]

Another question: I bought the meter (that I linked above) and tried it out in the crawlspace of my own house (not the vacation house of my OP). The level was about 5 pCi/L, above the EPA standard. But this was my crawlspace - I don't tend to hang out there So I've tried it in several rooms of the house itself, and readings are about 1 pCi/L. Should I be worried ?

I suspect if the vacation home were checked in areas above the basement (where the inspector checked it) that it would be in the safe range too. But I hope to finish that out to be a rec room or something, so it's still unacceptable.

Here is a link scroll down to page 12 For the risk table. It says .4 is outdoor air. 1 is low but not zero. Getting lower than that will be difficult. I did a grad graduate lab radon study of my condo many years ago now. The highest level I was able to measure was about 1 and that was in the bathroom with the shower running. For 15 minutes. My point if you are on well water check the water.
radon is an increased risk factor. Like driving or owning firearm or drinking. what is your risk tolerance. Lately I have been trying to avoid the most accident prone intersections in town, but haven’t changed my alcohol consumption habits. If I was to really look into the numbers I’m pretty sure I’d find reducing can’t my alcohol consumption would have a greater impact than avoiding a couple intersections.

https://www.epa.gov/sites/default/files/2016-02/documents/2012_a_citizens_guide_to_radon.pdf

 

[RustyShackleford]

Oh yeah, I wasn't worried about radon in mountain house (subject of OP), being town water (I have to believe they test that, but I suppose I should confirm).

But my primary residence, yeah, well water, never tested. I'll try running the shower awhile and stick the meter in there - but it takes it about 24hrs to read anything.

 

[EbS-P]

Wake and Franklin counties have testing available. Here is map. I found and the link.

Radon in Well Water | NCDHHS

www.ncdhhs.gov

Chances it’s in the water and is high are probably only if you live in the colored areas. My shower test was just to try to get something above background. The detectors I used had hourly sample times. Let the shower run 10 minutes every hour and keep the door closed might give you an indication that you need your water tested. I would check with neighbors and see if they have ever had the house or we’ll water tested.

 

[RustyShackleford]

Thanks for that link. I live in one of the kind of "spotty" areas.

 

[EbS-P]

Thanks for that link. I live in one of the kind of "spotty" areas.

With a well it’s worth sending a sample off to get tested. There was a link somewhere to get a list of companies that do the testing. An email or call to the county health department asking how to get a radon water test is probably a good idea. There were wells in Maine that the sample bottles literally opened like a soda bottle because of radon. We know much more about it (compared to 50 years ago) and have mapped the geological formations that are likely to contain uranium but when it come to wells unless all the wells around you are at the same depth there can be more local variability in radon water concentrations as opposed to living space. But to be clear even if it’s in the water it’s still the inhalation that’s concerning more than the consumption.

 

[RustyShackleford]

So I've had another look at the new vacation house ... Again, it has a "day basement" (partially buried in the hillside, partially completely above grade), a floor with the bedrooms above that, and the floor with the living room, kitchen etc at the top.

There is a hole in the plywood floor of the day-basement, where the sewage line and water line come through. There is definitely a vapor barrier down there, although I can't tell how good it is (seams sealed, etc). My inclination is to install a radon fan that sucks through that hole and vent to the outside - and see how that works. I'd come up from the hole with 4" or 6" PVC, seal around it good, and then go through the nearby cinderblock wall. There I'd install the fan. I'm not sure why everyone seems to put the fan outside, but Fantech and others make weather-resistant fans, so I guess it's not a concern. Fortunately, at the location that's most convenient to the plywood hole and to come through the cinderblock, there are no windows on the two floors of living space above the basement. So I feel good about not running a duct up to above the roofline - and, if I throw my skirts over my head and call in a pro - it'd be a great space to install the vertical stack.

I don't really foresee a problem though. As others have commented, my level isn't that high. I also put a radon meter (linked above in post #7) in the lower floor of the living space (the floor above the day-basement) and the reading was about 5 pCi/L - barely above the EPA guideline, although roughly double the EU one.

 

[EbS-P]

So I've had another look at the new vacation house ... Again, it has a "day basement" (partially buried in the hillside, partially completely above grade), a floor with the bedrooms above that, and the floor with the living room, kitchen etc at the top.

There is a hole in the plywood floor of the day-basement, where the sewage line and water line come through. There is definitely a vapor barrier down there, although I can't tell how good it is (seams sealed, etc). My inclination is to install a radon fan that sucks through that hole and vent to the outside - and see how that works. I'd come up from the hole with 4" or 6" PVC, seal around it good, and then go through the nearby cinderblock wall. There I'd install the fan. I'm not sure why everyone seems to put the fan outside, but Fantech and others make weather-resistant fans, so I guess it's not a concern. Fortunately, at the location that's most convenient to the plywood hole and to come through the cinderblock, there are no windows on the two floors of living space above the basement. So I feel good about not running a duct up to above the roofline - and, if I throw my skirts over my head and call in a pro - it'd be a great space to install the vertical stack.

I don't really foresee a problem though. As others have commented, my level isn't that high. I also put a radon meter (linked above in post #7) in the lower floor of the living space (the floor above the day-basement) and the reading was about 5 pCi/L - barely above the EPA guideline, although roughly double the EU one.

How long has the house been closed up? I’d be interested in seeing levels once it’s air out and then closed back up.

 

[semipro]

Just read that radon is the densest naturally-occurring gas, about 8X the density of air. I'm surprised this is even a problem, except it low areas, like basements, where it can collect.

Air movement upwards from the basement occurs though because of the stack effect.
Your plan to suck air from below the plywood subfloor in the basement and exhaust it outside sounds like a good thing to try.

 

[RustyShackleford]

Your plan to suck air from below the plywood subfloor in the basement and exhaust it outside sounds like a good thing to try.

No idea what size fan to use though. And 4" or 6" ducting ?

 

[EbS-P]

No idea what size fan to use though. And 4" or 6" ducting ?

How much air do you want to move? What the sq ft of the space. 6” could move same air as 4 but could be quieter. But it could be over kill too.
Another question is do you need a high static pressure fan?

Just to throw number out there. 1000 sq ft. We want to exchange a 7’ high space once a day. 7000 / 3600 Call it 2 cfm. 10x day would be 20 cfm. 4” would be fine with a 50 cfm fan. (All guess work) you should probably seek another opinion.

 

[stoveliker]

I think he is going to exchange only the air below the plywood? I.e. much less cubic feet?

 

[EbS-P]

I think he is going to exchange only the air below the plywood? I.e. much less cubic feet?

Yes I agree.

 

[stoveliker]

Also, I had to put in a system in my previous place. It was a low-flow system, as it generated a vacuum below the slab. Any gas coming in that space would be (somewhat slowly) sucked into the pump and exhausted.
I believe the situation here could be similar: create a vacuum under the floor, and due to the natural leaks of air into that space there will always be some flow towards the pump. The result is a low-flow system (so small ducts are fine), and a higher static pressure pump needed.

The low flow might give some concerns (of still a high concentration of radon), but given that below-slab systems work similarly, and there is a low flow that should prevent much accumulation (it's not the instantaneous odd Ra molecule, it's a concentration due to accumulation, above a threshold that's a safety issue), I think that should be fine.

I (not an expert) think...

 

[semipro]

I'd suggest starting with 4" duct and a variable speed fan. That way you can dial it down to the lowest acceptable level and meet your ozone level goals while minimizing energy use from the motor and house air infiltration losses.

 

[EbS-P]

I'd suggest starting with 4" duct and a variable speed fan. That way you can dial it down to the lowest acceptable level and meet your ozone level goals while minimizing energy use from the motor and house air infiltration losses.

I could be making this up but don’t some radon systems utilize pvc? Would this be the due to the high static pressure?

 

[stoveliker]

I could be making this up but don’t some radon systems utilize pvc? Would this be the due to the high static pressure?

Yes, my system was pvc.

 

[semipro]

I could be making this up but don’t some radon systems utilize pvc? Would this be the due to the high static pressure?

Yeah, almost all the ones I've seen do.
I meant "duct" in the generic sense.