Moisture at top of stud cavities
Hi all, I’ve found some moisture on the bottom of 10 stud cavity top plates, and probably the rest of the 75′ wall is similar. I drilled a hole 10′ away from the last open cavity and it seemed dry, but I saw evidence of previous moisture and a musty smell. Luckily, there is a horizontal drywall joint 10″ from the ceiling. The non-paper faced loose fiberglass batts are damp at the top 6″- two are moist as far as my arm can reach. Here is some background info:
Building located in SF
The wall assembly is 5/8″ cement board, tyvek wrap, probably 1/2″ or 5/8″ plywood, 5/8″ gypsum fire board, 2×6 studs, then 5/8′ drywall.
The building is two stories, each story has 16’8″ ceilings. I’m on the 2nd floor and the full 16’8″ exterior of my condo unit has clear SW exposure. The story below me is blocked by a next door building.
Above the wet cavities the wall extends upward creating a parapet wall 4′ above the roof.
The moisture seems to be condensation forming on the underside of the bottom top plate. There is another plate on top.
The previous exterior wood siding on the wall was replaced about 6 years ago. The wood siding was replaced with the cement board and tyvek.
The torch down roof was covered with a Dura-Last roof about 5 years ago. It seems solid.
I opened a hole in one ceiling cavity to check for moisture above the top plates and there was none.
Before I opened the wall, the worst cavity was warm to the touch on the interior drywall, while the adjacent cavities were cool (but were also moist when opened).
I suspect condensation. Attached is a picture of the worst cavity right after I opened it. I’ve since dried it out and covered the opening with sealed saran wrap to see if moisture returns. The saran wrap bulges out a bit, so there is some noticeable upward air pressure.
The previous wood siding was in bad shape before it was replaced. A lot of drywall screws I’ve inspected show evidence of rust all up and down the wall. The drywall 12″ from the ceiling and down seems fine- the rear paper is still in good shape- but it seems there was moisture all around. The top 10″ of drywall has to be replaced- the rear paper is mush. Luckily, there is a very small amount of mold. It’s unclear how long the moisture has been in the wall. I found this issue as I was removing blistered and cracking drywall tape all over the 16’8″ x 75′ wall. The tape generally pulled off easily.
Is it possible moisture was locked in the wall after the cement board and tyvek was installed and just now most of the wall is drying out? I guess this would be the best case, considering.
How can I check for air infiltration?
Should a dense packed insulation be installed? I’ll most likely activate insurance.
Any help is greatly appreciated! Sorry for the long post- let me know if I missed anything.
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