I just tested my new ICF house for Radon and found around 9 pCi/l. Anything over 4 is considered to be too high and requires mitigation. I was surprised at the test result because I used Forma-Drain for radon collection vented through the roof (but without a fan.) I've since ordered a fan to draw the gas out from under my basement floor with hopes it will cut the radon level to <4. I have an HRV for regular ventilation, but maybe the basement is not being ventilated sufficiently. My question is: Do ICF homes, by virtue of their tight construction, accumulate higher concentrations of radon than standard stick frame homes? My neighbors' stick frame homes don't typically have radon sub-floor ventilation.

Posted By Clark on 27 Apr 2010 06:18 PM Do ICF homes, by virtue of their tight construction, accumulate higher concentrations of radon than standard stick frame homes?

All tightly built homes will accumulate higher concentrations of anything that tends to be present - radon, humidity, BO, onion smells, pet odors,..... You get the idea. That's why the strong stress on using an HRV/ERV for ventilation. You may just be unlucky and have built above a particularly high emission of radon from the ground.

I don't remember now if it's the HUD website, or Building Science site, but one or both of them have some good suggestions for dealing with radon. If you haven't already you might check them out for suggestions. The fan in the exhaust tube like you say you have is one of the most common solutions.

I could be wrong but I'm thinking I've read something somewhere about fresh concrete emitting radon for awhile, if there was radon in the materials used to mix it.

I could be wrong but I think the fan won't do much. It will be like sucking on a straw that has the end folded over. You will have to introduce air into the Forma-Drain to allow air flow. From the radon mitigation systems that I've seen installed they usually have a inlet thru the band joist on one side and one going out the other. Did you use any type of under floor material like poly or somthing of that type?

Posted By smartwall on 28 Apr 2010 08:37 PM
I could be wrong but I think the fan won't do much. It will be like sucking on a straw that has the end folded over. You will have to introduce air into the Forma-Drain to allow air flow. From the radon mitigation systems that I've seen installed they usually have a inlet thru the band joist on one side and one going out the other. Did you use any type of under floor material like poly or somthing of that type?

Yes, the concrete floor in the basement was poured over 2" of XPS (pink board) covered with a layer of Tu-Tuf XF poly sheeting. I suspect the radon leaks into the basement at the junction of the floor and walls. I haven't installed the fan yet, but I'm hoping it will work. The Form-A-Drain is connected to the sealed sump which is vented to the roof. The vent should supply fresh air to replace the radon laden air expelled by the fan.

I installed the fan on the radon vent pipe running from the Form-A-Drain under the basement floor through the roof. After running the fan for 3 days, the radon dropped from 7 pCi/l to 1.5 pCi/l. Anything < 4 pCi/l is considered acceptable. I'm going to experiment to find what fan duty cycle is needed to maintain a safe radon level.

Technically, there is no such thing a a "safe" radon level. Any amount adds to your cancer risk.

That is the popular perspective....

Posted By jonr on 08 May 2010 07:28 AM
Technically, there is no such thing a a "safe" radon level. Any amount adds to your cancer risk.

I understand your point, jonr, the only truly safe radon level is zero. I should try to reduce my radon level as much as I can. The cost is only a few kilowatts a year to continuously run the fan. I'm curious, though. How many ICF homeowners have tested for radon? When I asked my next door neighbor what his radon level was, he didn't know. He was suddenly concerned when I told him that my reading was elevated. We measured his traditionally built house at 1.7 pCi/L. He was satisfied with that. ICF homeowners: Have you tested for radon?

Please. The ICF has nothing to do with it and you know it. Your post above with picture says "running from the Form-A-Drain under the basement floor". Choosing to build a house sloppy so that it will leak is not the solution to the problem. Regards.

Texas, I'm not trying to slam ICFs and I don't advocate building "sloppy" as a solution to high radon levels. I am suggesting that building with ICFs requires a heightened awareness of the radon problem potential and the need to provide for possible mitigation. Point me to a study or source that proves or demonstrates that a tightly built house whether built with ICFs, SIPs or whatever, is more or less prone to increased radon accummulation than conventionally constructed houses. I think my question is reasonable. My house was built tightly with ICFs. My next door neighbor's house was built conventionally. I require an active radon mitigation system and his doesn't. Why should I not conclude, or at least suspect, that tightly built homes are more subject to high radon levels? Since most ICF houses are built for low air infilation, shouldn't ICF builders and owners be more sensitive to potential radon problems? If not, why not?

Why not just avoid the unwanted implication and say "tight house builders and owners should be more sensitive to potential radon problems"?

I'm not sure sloppy construction has any thing to do with it. Here in the northeast and other areas radon can be a problem. Kudos to Clark for his description of his problem and his fix.

Clark, I am glad you have this resolved. I went back through the post and also did a little digging (figuratively).. and one thing does come to mind. If you could start from scratch it might have been better to use cincoflex (or other) between the basement floor and the walls. Clearly, if the stuff can't get in it can't accumulate. Further, if in fact this is where it's getting in - what if you sprayed an air tight sealer like close cell over the area perhaps cover the floor and the first part of the wall and then tile over or similar. Just a thought. Regards.

Clark, one further thought.  Some time ago claims were made regarding air quality (in regard to ICF) for schools due to the tightness of the walls.   Tests were performed and it was determined that the air quality on the outside was worse than the air quality inside.   Regards.

Posted By TexasICF on 09 May 2010 05:27 PM
Clark, one further thought.  Some time ago claims were made regarding air quality (in regard to ICF) for schools due to the tightness of the walls.   Tests were performed and it was determined that the air quality on the outside was worse than the air quality inside.   Regards.

This was my initial thinking.  Having taken precautions to seal the basement foundation and floor, I expected that the radon level would be lower than with a conventional poured concrete basement.  You can imagine my shock when the measurement came in so high.  In any case, the steps I've since taken have worked beautifully.  My long-term radon level reading is now down to 1.2 pCi/L.  Most people I've talked to haven't measured their radon levels, unless it was required in the sale or purchase of the home.  I now believe it's a good idea to do so.

Posted By Clark on 08 May 2010 08:40 AM

Posted By jonr on 08 May 2010 07:28 AM
Technically, there is no such thing a a "safe" radon level. Any amount adds to your cancer risk.

I understand your point, jonr, the only truly safe radon level is zero. I should try to reduce my radon level as much as I can. The cost is only a few kilowatts a year to continuously run the fan. I'm curious, though. How many ICF homeowners have tested for radon? When I asked my next door neighbor what his radon level was, he didn't know. He was suddenly concerned when I told him that my reading was elevated. We measured his traditionally built house at 1.7 pCi/L. He was satisfied with that. ICF homeowners: Have you tested for radon?

Radon levels in the outdoor air in some locations is well above the 4pc/l remediation level- getting it down to an a completely undetectable level is usually not an option.  Average outdoor air radon in the US is below 0.5pc/l, but if your outdoor air is 9pc/l, no amount of remediation will get it below that. (But with a neighbor's indoor reading of 1.7pc/l there's hope, eh?)

How do you get it down to a few kilowatt-hours (not kilowatts)/year?  Even the smallest 35W fan  (0.035kw) times 8760 hours/year chews through 300kwh in a year, and most radon fans are 65W or bigger.

Slab depressurization doesn't require a dedicated air inlet to work, and may make it work less efficiently- don't knock yourself out making an air inlet. Using passive (wind activated) depressurization with venturi-type or turbine-type ventilator caps on the existing radon stack can provide sufficient additional depressurization in some instances.  (The venturi-types work better at very low wind speeds, and can be used in conjunction with an active radon fan.)

Heat recovery ventilation (HRV or ERV) at ventilation rates required to control humidity levels in very tight homes are usually sufficient to reduce radon levels well below the 4pc/l recommended remediation level. Ventilation rates can be increased above the humidity-control level if needed, at a lower cost in additional power than an active radon-only slab-depressurization system.  Spending the money on an ERV/HRV system is usually money better-spent than spending it on active slab-depressurization.  If you already have an HRV, boost it's duty-cycle a bit and re-test.

Posted By Dana1 on 11 May 2010 02:01 PM

Heat recovery ventilation (HRV or ERV) at ventilation rates required to control humidity levels in very tight homes are usually sufficient to reduce radon levels well below the 4pc/l recommended remediation level. Ventilation rates can be increased above the humidity-control level if needed, at a lower cost in additional power than an active radon-only slab-depressurization system.  Spending the money on an ERV/HRV system is usually money better-spent than spending it on active slab-depressurization.  If you already have an HRV, boost it's duty-cycle a bit and re-test.

I already have an HRV, Dana.  As I pointed out in another post, running my HRV during these damp spring days raises my indoor relative humidity well above 50%.  I'm running a dehumidifier to keep the rh <50% for comfort and to protect my hardwood floors.  Boosting the duty cycle of my HRV as a means to reduce the radon level would require a lot more energy (with dehumidification) than running a small radon fan.  

As you pointed out, I understated the cost of running the radon fan continuously year round.   For me it comes to about $40/yr, not an insignificant amount.  If I understood you correctly, continuous operation of the fan shouldn't be needed, however.  The HRV should do the job at least during the heating season.

I would have a similar issue with an HRV at high duty-cycle increasing the latent loads in my house too, although perhaps not as much of the year as you.  (For me it would be primarily June-August.)  Over-ventilation as a means of radon mitigation is better suited to climates where dew-points above 50F aren't typically sustained for days on end, which is still a large portion of western N. America, but not much of the eastern US, particularly the southeast.) But seasonally it should work too.  Smart controls that could switch between HRV & radon fan based on outdoor dew point would be ideal, but SFAIK none are commercially available.

You don't need to go as low as 50% RH to protect hardwoods- they'd be happy even at 65% RH (but not 70%).  Humans tend to be less comfortable over 60% RH, and those with dust-mite allergies need to limit it to 50% to keep the mite population in check.

Posted By Dana1 on 11 May 2010 04:50 PM
I would have a similar issue with an HRV at high duty-cycle increasing the latent loads in my house too, although perhaps not as much of the year as you.  (For me it would be primarily June-August.)  Over-ventilation as a means of radon mitigation is better suited to climates where dew-points above 50F aren't typically sustained for days on end, which is still a large portion of western N. America, but not much of the eastern US, particularly the southeast.) But seasonally it should work too.  Smart controls that could switch between HRV & radon fan based on outdoor dew point would be ideal, but SFAIK none are commercially available.

You don't need to go as low as 50% RH to protect hardwoods- they'd be happy even at 65% RH (but not 70%).  Humans tend to be less comfortable over 60% RH, and those with dust-mite allergies need to limit it to 50% to keep the mite population in check.

I've read that indoor humidity should be controlled in a 20% range to avoid damage to hardwood floors.  For example, 35% to 55% rh assuming the floor material was acclimated and installed at 45% rh which is what my floor manufacturer recommends.  My floors were installed at ~40% rh, so I'm reluctant to let the indoor humidity go as high as 60% for more than a day or two.   I keep my house a little on the dry side in winter to minimize the risk of condensation in the ceiling space (3" closed cell polyurethane SF over R25 fiberglass batts, no vapor barrier, 6500 HHD.)

Dana, since my radon sub-slab venting system includes a perimeter collection channel (Form-a-Drain) and a 28' x 4" vertical stack, does it make sense to run my radon fan on a reduced duty cycle shooting for, say, < 2 pCi/L?  I'm at 1.2 now running 24/7.  jonr reminds me that there's no "safe" radon level, but the cancer risk gets very low at that level.

why not plug it into a light timer type device and set it to run 3 hours in the morning and 3 hours in the evening.  See how your levels are after that and adjust up or down accordingly.