inspectorD

The technical stuff we could give you will not help anyway. The issue with this is going to be a wait and see. We do not know how much vapor is moving through the area above. You could seal the concrete above and limit the vapor flow also. This area probably does not have to be taped and finished right away anyway. Install what you have temporarilly with no finishing touchs and see what you end up with in the summertime humid months.
Just a suggestion.

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Just My
Made in the

Quattro

That's kind of the plan, I guess (the "wait and see" method). The concrete step outside does need to be refinished and sealed (some exposed aggregate and the seam that needs patching).

However, how will I know if it's working? Wouldn't I have to pull everything off and check the condition of the concrete? That would be a hassle, but not as bad as having to pull drywall down I guess.

Also ToolGuy, the plastic isn't about the expense or time, it's about whether adding that vapor barrier would trap moisture between itself and the foam. I'm basing this assumption on other things I've read about having 2 vapor barriers on the interior side...

Anyway, thanks for the continued help and ideas. I'm going to spend the rest of the winter getting the rest of the basement insulated in a similar way. Luckily, this is the only place where water was an issue...the rest of the basement is very dry.