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iamjonwalker 12-17-2012 11:01 AM

Radon mitigation in inaccessible crawl space...
 
Long time reader, first time poster. I have been doing lots of research on the subject and figured I'd post my situation to get some accurate advice...

Just purchased a 2-story 800 sq. ft. home near Chicago, IL, it's a 100 year old bungalow on a hillside. It sits on a post and beam foundation, subfloor is uninsulated plywood and underneath a virtually inaccessible unvented dirt "crawlspace", so I can't completely encapsulate unless I rip out the entire basement (bathroom, laundry room, 2 bedrooms), which isn't an option for me now. There is 6mil plastic laid down as a vapor barrier but not sealed. The radon level is averaging around 8.7pCi/L, according to my Safety Siren Pro radon meter.

As of now, my plan is to seal any cracks I can between the crawlspace and subfloor. any sealant suggestions? plastic? felt paper? what about insulation? (i'll probably carpet eventually) then if the levels are still high, install some kind of vent (fan? heat exchanger?) in the crawl space, there is about a 2 ft. clearing on about 30% of the area and between 4" and 1' on rest of the space between the dirt and floor joists. I haven't been here for a summer yet so I'm not sure what the humidity will be like but I'm assuming from the visuals of the 100 year old crawl, proper outside gutter drainage and being on a hillside, there isn't much moisture getting in there. Additionally, I do not have AC so the windows will be open most warm days, therefor if the radon levels are being diluted that way, I may be able to avoid pumping the humid air into the crawl space. One thing that is concerning/confusing about installing a vent/fan is pressurization, any clarification on the matter pertaining to my specific situation would be helpful.

Any advice, thoughts or ideas before I do any more work is greatly appreciated!

md2lgyk 12-18-2012 07:04 AM

Having worked almost 40 years in the nuclear industry, I know a bit about radiation and radioactivity. Take it from me, radon mitigation is a scam and a waste of money. There are many, many things in the environment that are far more dangerous and can sicken or kill you long before radon ever will.

iamjonwalker 12-18-2012 11:25 AM

md2lgyk:
Thanks for the input. I don't think radon gives off radiation, but the "harmful" gas is supposed to increase your risk of lung cancer. I have my doubts too but would rather be safe than sorry, especially for a kid sleeping in the basement.

To you and the rest, to clarify my "questions":
I'm interested in sealing off the subfloor from the crawl space, if not for radon then just for the musty smell and heat loss. I can't get down there or the boards up easily to insulate. I'm considering a few things but unsure of their cost/effectiveness (I'm on limited budget, focusing on functionality over looks):

- seal cracks with wood filler, paint and polyurethane, it might look fine like that or at least it would be sealed to laminate or carpet

- lay down plastic or felt paper then laminate or carpet

- laying something like rigid foam board over existing plywood then installing new subfloor on top. seems like it would be expensive but the floor would be insulated

Then, if the radon/humidity levels in the crawl need to be dealt with, I'm thinking something like an air exchanger or fan powered vent. Should I be concerned with pressurizing assuming as the subfloor is completely sealed?

tylernt 12-18-2012 11:56 AM

Quote:

Originally Posted by iamjonwalker (Post 1075321)
- lay down plastic or felt paper then laminate or carpet

I know nothing of radon, but in our house there is a plastic vapor barrier between layers of subfloor, and I would think that would better than any kind of liquid application. Buildings move, and when they move, liquid products can crack. Plastic will just stretch and maintain air seal integrity.

Quote:

- laying something like rigid foam board over existing plywood then installing new subfloor on top. seems like it would be expensive but the floor would be insulated
Have to be careful insulating floors. You need a vapor barrier on the warm side, so that moisture does not migrate from the living space and condense on cold wood in the winter where it will mold and rot. Foam by itself is usually a good vapor barrier, but you need to do something with the seams. Perhaps the metal foil tape designed for sealing HVAC ducts?

Quote:

Then, if the radon/humidity levels in the crawl need to be dealt with, I'm thinking something like an air exchanger or fan powered vent. Should I be concerned with pressurizing assuming as the subfloor is completely sealed?
You should not pressurize. You will never be able to perfectly hermetically seal the living space from the crawlspace, so pressurizing will drive radon into the living space somewhere, somehow. If you must have a fan, install an exhaust fan to suck air out of the crawl. Then the worst that happens is a bit of conditioned air is sucked out of the living space... yeah, that might hurt your heating bill a tiny bit, but much better than the alternative.

If you were in a dry climate I'd say yeah, go for it with the power fan. However in the summertime I worry about introducing all that humidity which will condense on the cool wood and mold and rot. Not sure what the best solution is there... maybe just skip the fan entirely, and depend on your air sealing to do the job.

iamjonwalker 12-18-2012 12:42 PM

Thanks for the reply Tylernt...

I worry about sealing either plastic or foam board (or paint for that matter) on top of the plywood subfloor because it would be trapping all that moisture underneath, which is why I think a fan is going to be necessary regardless.

Regarding insulating, the floors aren't that cold, should be warmer when I put something on top and heat rises, so I can't image I'm losing too much heat in the winter, especially if I seal well. Plus, I don't have AC so theoretically, not insulating the floor from the crawl space will actually cool the home in the summer?

So, maybe I should just use plastic (6mil?) to seal as it will be the easiest and cheapest option, it will act as a vapor barrier (water, radon, odor) and if it is trapping moisture underneath, it will be the easiest to remove and rethink?

tylernt 12-18-2012 01:14 PM

Quote:

Originally Posted by iamjonwalker (Post 1075357)
I worry about sealing either plastic or foam board (or paint for that matter) on top of the plywood subfloor because it would be trapping all that moisture underneath, which is why I think a fan is going to be necessary regardless.

Well unfortunately I don't know much about how things are supposed to work in a humid climate, all I have to work off is the presence of plastic in the subfloor of my semi-arid home. Hopefully someone from one of the "damp States" can answer that one.

Remember though, it takes humidity of a certain minimum level to start growing things. Moisture of a lower concentration is no problem, so you don't need things to be bone dry to be safe.

Quote:

Regarding insulating, the floors aren't that cold, should be warmer when I put something on top and heat rises, so I can't image I'm losing too much heat in the winter, especially if I seal well. Plus, I don't have AC so theoretically, not insulating the floor from the crawl space will actually cool the home in the summer?
I've only ever lived in houses with uninsulated floors. Never bothered me if there's carpet or vinyl (tile gets unpleasantly cold). So yeah, I don't see an urgent need to insulate... just if you want to.

Quote:

So, maybe I should just use plastic (6mil?) to seal as it will be the easiest and cheapest option, it will act as a vapor barrier and if it is trapping moisture underneath, it will be the easiest to remove and rethink?
Sounds good to me, although if there is a moisture problem, I would hope it could be addressed with venting rather than removing the plastic.

md2lgyk 12-18-2012 01:27 PM

Radon is a tasteless, odorless, colorless, radioactive gas that is found in the soil practically everywhere on Earth. Like all radioactive elements, it decays (ultimately to lead) by various stages of particle emission. In the case of radon, these are primarily alpha particles. Because they are so easily stopped (even your skin will block them), alphas are a hazard only when the radon is inhaled, where they can damage fragile lung tissue. But radon is heavier than air, so it will NOT permeate your entire house. And, by the way, do you realize you have at least one other radioactive substance in your home?? Smoke detectors contain Americium-241. Don't hear about the hazards of that, do you?

There is no absolutely safe level of ANY radioactive substance. But you would have to live 24/7/365 in a space with much higher levels than you have to stand even a remote chance of getting cancer because of it. That's why residential mitigation is such a waste of money.

tylernt 12-18-2012 01:37 PM

Quote:

Originally Posted by md2lgyk (Post 1075381)
But radon is heavier than air, so it will NOT permeate your entire house.

I will definitely defer to your expertise on radon. However, you can get a "stack effect" -- like a chimney -- on a hot day when an improperly vented attic attains a slight negative pressure and pulls air from improperly airsealed living spaces. In turn, this could pull air from the crawlspace. Air infiltration can occur around plumbing fixtures, receptacles, light switches and fixtures, improperly sealed HVAC ducts... really any penetration in the floor, ceiling, or walls. Sometimes even through sole plates, which shows up as dust on the carpet along the baseboard.

In a properly functioning home, I agree, no air should be pulled from the crawl. In a poorly constructed or maintained one, you could potentially have issues. I think airsealing is a good idea from an energy efficiency perspective, even if radon is not a concern.

iamjonwalker 12-18-2012 01:54 PM

air sealing with plastic... could I just lay laminate on top of that? If I am doing carpet, how would I fix it to the floor without breaking the plastic?

tylernt 12-18-2012 02:04 PM

Quote:

Originally Posted by iamjonwalker (Post 1075390)
air sealing with plastic... could I just lay laminate on top of that?

If you do a floating floor (click-lock), you generally need to put down a resin paper underlayment. The plastic would go under the paper.

If you're doing sheet vinyl, plastic won't work with the glue. Vinyl is pretty airtight by itself though, so I would just glue it down to the existing subfloor and call it done.

Quote:

If I am doing carpet, how would I fix it to the floor without breaking the plastic?
You'll only penetrate the plastic around the edges of floor by the walls, where the tack strips are nailed down. I don't think air will be able to migrate around the nail holes.


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