Radon mitigation in inaccessible crawl space...


Old 12-17-12, 03:55 PM
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Join Date: Dec 2012
Location: United States
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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!
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Old 12-18-12, 09:30 AM
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Join Date: Dec 2012
Location: United States
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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?
Old 12-18-12, 01:52 PM
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I know very little about radon mitigation but from what I've heard/read, I think it's mostly done by sealing the lowest floor [crawlspace] and then using air ventilation for anything that escapes the plastic.

Floor insulation is best addressed by insulating the void between the floor joists. I don't know if there would be any benefit from sealing the sub floor. Solvent based coatings do seal better than latex coatings. I'd be leery of building up the floor too much as it may cause problems with doorways and baseboard.

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