"Nate Nagel" wrote

least a DIYer more experienced than I.) I suspect that the other water is
coming in behind the large board that's attached to the outside wall of
the house to support my deck. I'm thinking that flashing between the
decking boards and the framing is probably the answer here? Any
tips/how-tos on how to do this on a brick wall? I was planning on redoing
the decking boards anyway next year so this is not a huge deal.

If you are re-doing it soonish, then I'd apply a large amount of caulking
around that area for now.