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Old 03-25-2008, 06:32 PM   #1
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Tyvek application in crawlspace

I have a question about the use of TYVEK housewrap to hold up fiberglass insulation in a vented crawl space. We had two additions put on and the contractor replaced the fiberglass bats in the original home along with putting fiberglass bats under the new addition. We had him change the original home insulation under the house because some pieces were starting to fall down and the paper vapor barrior was installed incorrectly. The original builder of the home stapled the flaps of the fiberglass to the joists so the vapor barrier was facing the vented crawl space not the flooring. (We live in Pennsylvania.) Myself and a heating contractor crawled under the house in July and the heating contractor exclaimed "You got a tropical rain forest going on under here"! The TYVEK housewrap was literally dripping and puddling with water. Further inspection showed missing pieces of bat insulation, not properly insulating around sewage drain pipes, and cracks and crevices where small pieces of insulation should have been cut to fit in places were non existent.(I have pictures of the poor insulation job.) My theory is cold air from the air conditioned living area above found its way through those openings, met with the summer high humidity air that filtered through the TYVEK or above the TYVEK air space, condensed and literally allowed my wood joists to be inches away from puddles of water held by the TYVEK. My original home had 4 mil plastic vapor barrier laid down over the dirt but the seal along the cement walls pulled away after 17 years. The contractor refused to put any plastic vapor barrier over the new additions crawl space dirt floor stating, "You don't need the dirt covered". My house sits on top of a hill and I've never seen that bad of a sweating problem like that ever before. Have you ever heard of this before? Is my theory correct? I've contacted TYVEK and they gave me a confusing answer although a rep is supposed to get back to me. I was told that TYVEK housewrap is not speced to be mounted in the horizontal position yet it is perfectly fine to be mounted under flooring in a vented crawl space covering the fiberglass insulation bats. I have already torn down the TYVEK for fear of wood rot and mold issues. I called TYVEK because I felt they should be warning installers that if a poor installation of insulation is done in vented crawl spaces and then TYVEK housewrap is then used, they are creating a serious moisture problem in the summertime. Am I crazy for wanting to warn them about the use of their product in this application?


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Old 03-25-2008, 08:52 PM   #2
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Your main problem besides the insulation issues is that tyvek is only an air barrier NOT a moisture/vapor barrier in any way. It is likely not doing anything to cause or cure your problems. That moist summer air coming thru the vents is going to condense in the cooler crawlspace regardless if you seal off the room above. Alot of new work is going into sealing off the vents and making a closed crawlspace instead of the vents which like said allow a path for moisture laden air in the summer and super cold air in the winter. Also when the crawl is sealed up the walls of the crawlspace are whats insulated not the floor above and xps pink foamboard is used instead. 6mil poly goes on the floor and up the walls all seams overlapped by 12 inches or more and taped sealed.


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Old 03-27-2008, 09:55 AM   #3
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craw space sweating

call me stupid but i am still lost about how to fix the problem with sweating under the house. i live in kansas. the vents have all been closed for the winter. i looked under the house the other day and it looked like it was raining. winter is over now so i opened all the vents, hoping to fix the problem. what is causing this? thank you
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Old 03-27-2008, 11:45 AM   #4
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You aren't suppose to close the vents in the winter.

I agree with Jaw that the best way is to insulate the crawlspace walls and make it a conditioned area rather than ventilate it, particularly in some climates. In effect your crawlspace becomes a mini-basement.
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