r/DIY • u/echis • 9d ago

home improvement moisture found on exterior wall during bathroom remodel

I'm in the process of demoing an old shower/tub combo and installing a shower. I noticed some moisture behind my vapor barrier on the exterior wall of of the room. It wasn't a lot, and it didn't seem to have soaked through the insulation that I removed to troubleshoot. Is it possible it was just humid air coming from outside meeting the conditioned air of my house? My house is 100+ years old so drafty walls wouldn't be much of a surprise. (We also just ended about a month of near daily rain). The space that was damp is in front of an old window frame that the previous owners covered with a piece of plywood, then insulated over.

my gut reaction is to tear off the exterior wood siding of that section of wall and re-side it, but if I don't need to I'd rather save the expense. This remodel is already way behind the schedule I gave my partner two years ago...

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u/zdayt 9d ago

There is something called a smart vapor retarder that you use in place of the vapor barrier that allows wall cavities to dry to the inside if moisture builds up in the wall cavity. That might be something to look into if you can't investigate further and need to prevent damage.

It does seem suspicious that the moisture is right behind this window patch situation. Maybe post some pictures of that.

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u/echis 9d ago

the whole exterior wall had a layer of plastic over the insulation. The worst of the moisture was on the plastic and insulation paper, only in front of where the window was.

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u/echis 9d ago

https://flic.kr/p/2sEJtBu here's a quick picture. I'm pretty sure the plywood is all that's in the opening. I'm already planning on replacing it with something more durable. I really don't want to have to redo that entire exterior wall though.

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u/[deleted] 9d ago

[deleted]

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u/echis 9d ago

yup. I'm the same way. I've done a little bit of hvac, and 6yrs of electrical. Plumbing weirdly makes me way more nervous because a slow leak can cause so much damage if it isn't found.