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drm31078

Condensation on TOP of vapor barrier

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Hey folks, it's been a bit humid here the last few days in Charlotte, NC. I was in my crawl space (which is covered by a vapor barrier) and when I put my hand down it felt moist. To my surprise it was moist. There is a tiny bit of condensation on top of the entire vapor barrier. All the vents are open and the ceiling is insulated. Should I be concerned or is this normal. The house is 4.5 years old and I do not see any signs of mold or wood rot. I assume this is just because the air is really warm and the ground is cold?

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"I assume this is just because the air is really warm and the ground is cold?"

I would agree with that.

Should I be concerned or just assume it's a once in a while event. Or...when should I be concerned?

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Is this the first time you noticed it or just the first time you checked? As long as the crawl space is properly vented and it's not water/moisture from below the barrier, then I would say no big deal.

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. . . I assume this is just because the air is really warm and the ground is cold?

Congratulations. You've discovered "condensation." I'll alert the Nobel committee.

- Jim Katen, Oregon

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Ummm...I am not in the crawlspace all the time, but when I do it's usually dry (no musty smell or anything). However, I have noticed the dirt on the vapor barrier looked like droplets, as if water was on the plastic at some point. So I assume it has happened previously.

I am pretty sure its not coming from under the vapor barrier. I will say the installation of the vapor barrier is not great (no spikes or tape), but it definitely covers more than 80% of the crawl space. I bought a humidity monitor to see what kind of humidity is in there going forward. What is a normal humidity level?

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After reading Jim's and Bill's links, I would have never guessed that radiation coupling would be a more dominant factor than convection currents...in both the attic and the crawlspace. It explains a lot about why envelope design needs to be so different in the South.

Excellent links.

Marc

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Hi,

If you haven't read the links yet, just understand that vapor moves from where it's more humid and warm to where it's cooler and drier. In NC in the summer months, the humidity outdoors exceeds that in the crawlspaces and all of that humid exterior air wants to get into that cool crawlspace. Once in there, it condenses on every surface cool enough to take it down to dewpoint.

Close the crawlspace vents and make sure that you have 100% tight coverage of the soil under the home. With any luck, your crawl will reach equilibrium with the outdoors and the vapor drive will stop and things will more or less dry out.

Advanced Energy Corp. is right there in NC and they have a better understanding of crawlspaces, especially eastern seaboard crawlspace, than anyone else on the planet - even Dr. Joe. Visit their crawlspace knowledge website at: http://www.advancedenergy.org/buildings ... wl_spaces/

If you can't solve it yourself, give them a call and see what they recommend.

ONE TEAM - ONE FIGHT!!!

Mike

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Hi,

If you haven't read the links yet, just understand that vapor moves from where it's more humid and warm to where it's cooler and drier. In NC in the summer months, the humidity outdoors exceeds that in the crawlspaces and all of that humid exterior air wants to get into that cool crawlspace. Once in there, it condenses on every surface cool enough to take it down to dewpoint.

ONE TEAM - ONE FIGHT!!!

Mike

That suggests convection currents are in play. My take on Joe L's explanation is that the dominant mechanism here is the radiation of heat from the underside of the floor joists and insulation to the cooler earth. The reduction in temperature that results from it is enough at certain times of the year and in certain climates to put the joists and insulation below the dew point of the air in the crawl. Condensation results.

Migration of water molecules in the air from a point of higher concentration to a point of lower concentration in the crawl may occur to replace the moisture that has condensed into liquid water but that's not the same mechanism as convection currents.

Maybe we just have two different ways of seeing the same thing.

Just a suggestion.

Marc

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Thanks for all the info...looks like this is expected. I bought a humidity monitor to see what the humidity level really is. Over the past 2 weeks, I have had a max of 79% humidity (this is not prolonged, just a max). I checked to see if there is condensation, but there was none.

Not too sure what to do. I have been in the house 4 years and just noticed the condensation issue. The wood and insulation all look to be mold/rot free.

When should I take action if at all?

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