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Cause/source of moisture

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What is the cause/source of the moisture – condensation? Recently performed an inspection on a home and found moisture, mold and even dripping condensation on the end and header joists visible inside the crawlspace. The moisture was also on the wooden subflooring where it abuts the end and header joists. Moisture was detected when I removed the fiberglass insulation. Moisture and mold was around the entire perimeter of the home. Insulation was fiber glass only, no paper backing. Other details – home was built in 2007, crawlspace with vapor barrier and 4 inches of gravel under the vapor barrier, outside temperature was approximately 45 F, down draft heating/cooling system with ducts running in the crawlspace, vinyl siding, attached garage (moisture was even along joists in the area and the front concrete porch). 5 of the 6 crawlspace vents were closed, but with the temperatures we have been having seemed normal to have the vents closed. Good positive grading around the exterior of the home. The rest of the subfloor and joists were clean with no signs of moisture, or mold. Possible causes that came to mind – Was the exterior of the house wrapped with Tyvex?, Was there rigid insulation installed before the siding was installed?, Is there a lack of insulation in the at the base of the walls? Please see the attached pictures. Any thoughts or comments are welcome.

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Whoever fixes that will need to determine whether it's water leaking down from the wall above or whether it's just condensation forming in the crawl.

If it's leaking down from above it could be a wall without insulation where the inside of the wall is alternately frosting up and defrosting. It might be a wrong-side vapor barrier installed in the wall plane or it might be a slight plumbing leak in an exterior wall.

Was this rim by any change behind a concrete slab porch where vents couldn't be installed?

If I were to see that here, I'd say that it's a cold rim, vapor escaping the barrier, closed vents and insulation preventing air from drying out the condensation on the rims - especially if the floors were uninsulated and the only insulation was that stuffed against the rims.

Seal the barrier tight to the ground, ensuring 100% coverage with no evaporation escaping. Insulate the under-house plumbing really well, clean up that mess with soap and water, dry it, nuke those areas with borate (I'd install Impel® rods and hit everything within four feet of the rim with BoraCare®), then insulate the rim, and subfloor within two feet of the rim, with spray foam or custom-cut EPS foam blocks sealed at the perimeter with Daptex or Great Stuff and then reinstall the floor insulation - stopping a foot short of the rim - and lastly open up the vents.



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I prefer the 'custom cut EPS' approach, it's DIY friendly and easily reversable in the event a repair is needed later. Panels of 1 1/2 or 2" are enough to shift the dew point off of the rim surface and into the foam where you want it. I would cut them for a snug press in fit and secure them with a bedding bead of silicone caulk at the top and bottom of the rim joist, and fill any gaps in miss cut foam as you go. I don't normally recommend silicone but the solvents in most other caulking will desolve the EPS. Spray foams are great but they're messy and expensive, both of which make it less than DIY friendly.

As Mike said, clean and treat that mess first and open up some vents.


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