Just moved into a 3 year old house in SW Missouri and am getting ready to insulate the crawl space. I went down there to measure up and noticed condensation on the NW corner of the poured foundation wall, about 18″ or so out from the corner on both sides of the wall. I then looked up at the rim joist and it was also wet from condensation, especially in the corner, and continued along the top edge of the rim joist on the north side of the wall for 15-20 feet or so. There didn’t seem to be any evidence of the condensation continuing down the rim joist along the west wall. The dirt floor is covered with about 3″ of gravel, no poly, and dirt underneath seems dry. There is about 42″ of clear space between the bottom of the joists and the ground. Outside there is plenty of slope away from the house on the north, west, and south sides. The east side could stand to have a little more slope to it, but I think its adequate. Also, on the north and west sides about two foot of the foundation is above grade. The west end of the south side starts at 2 foot exposure and slopes up to about 8″ of exposure on the east end and along the east side.
After searching this site this evening for “crawl space condensation” I found and read several threads on this subject and after reading them my plan is to first seal up the foundation vents, there are a half or dozen or so along the north foundation wall and the same number along the south foundation wall (8×16, located in the rim joist). I had closed all these vents several weeks ago since it has been quite cool here and we have been running the gas furnace for most of October. Next I place 6 mil poly on the floor, on top of the gravel I suppose, and somehow seal it to the foundation wall. And finally I plan to hang R-25 insulation batts, the encapsulated type, from the bottom of the subfloor to the top of the ground against the foundation wall.
I would be interested in any comments or suggestions anyone might have to offer. For example, should I seal the vents and apply the vapor barrier to the ground and monitor the situation to see if the condensation disappears before applying the insulation?
When I do apply the insulation is it important to also cover it with a vapor barrier or to seal the seams between batts?
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For further info check out http://www.buildingscience.com/
Keep in mind, there are lots of different views and what works in one area might not work in another.
Don't be fooled by dry soil. How do you think it got dry?
Bob,
Thanks for web site link. I briefly checked it out and will definitely go back and study that information in depth. Lots of good stuff there, I just wish the builder of this house had read it. I'm somewhat limited in what I can correct for a reasonable cost at this stage.
In rereading my original post I didn't specifically ask, but, why am I seeing a concentration of condensation only in the N.W. corner of the house and nowhere else? Is that just the only corner that is below the dewpoint or is there something else in that area that increases the moisture in the air? I did not see anything unusual, but I probably not experienced enough to know what to look for. Any ideas out there?
I've been busy this AM and didn't read your full post, but yes, it is not unusual to see condensation only in localized areas, although not common in crawl spaces. (More typical in attics, where there far higher likelihood to see mildew on the north side sheathiong than the south.)
I am in the KC area and while fall is here it has not been that cold yet.
This is 90% speculation, but my guess is that you are seeing is not condensation from warm moist air from the house condensating. But rather it left overs from this summer when we had LOTS of hot moist outside air hitting the nice AC'd house. BTW, are there any ducts in this area and might there be a leak.
There are no ducts really that near this corner. I did find one obvious duct leak (there was a 1/2" open gap at the bottom where an elbow connects the run to an outlet, but this was on the opposite side of the house. All of the ducts are ridgid metal covered with 1.5" fiberglass wrap that has a plastic covering over it. In several places, including where I spotted the gap, the insulation doesnt cover the connection to the outlet. None of exposed metal ducts appeared to be sweating. There is a downspout at this corner which just dumps onto a splash block. Perhaps I should extend that a little farther away from the house. I guess there is a chance that the increased moisture in the ground near that corner could be keeping the foundation corner cooler? Or perhaps as you suggest seeping thru, although no cracks were evident.
Of course too, there appears to be condensation along the upper edge only of the rim joist as you go along the north wall and the condensation seems a little heavier as you get near a foundation vent.
Thanks for the comments!