Minnesota
50’s rambler with a few additions over the years.
I believe it is cement board siding with brick veneer around the lower base.
Blower door test came in around 4,500 cfm50

In searching throughout my home to seal air leaks and find ways to increase insulation I came across a particularly vulnerable spot in my crawlspace that breaks off from my basement storage room. The crawlspace has concrete blocks on one wall and that is mostly above grade and then on the further wall there is a stud framed wall above grade filled with pink fiberglass with poly overtop attached to the studs and brick veneer on the exterior side finishing it. This stud framing is sitting on top of concrete blocks as well, and the floor is a poured slab of concrete.

There are multiple weak points i would like some help with:
On the far left bottom sill and far right bottom sill for the stud framed wall over the concrete blocks it looks like the mortar fell away into the block cavity and air is openly rushing in. What would be the best way to fill this as they are pretty big holes? Stuff some roxul in there as a backer and then foam?

Next, at the rim joist above the stud wall there is all sorts of nonsense going on it seems. First, there is not a continuous rim joist. There is a screenporch/ deck that is starts outside of the stud wall, with the joists coming through and resting on top of the stud wall/ brick veneer. Then it looks like there was 2x8s or maybe 2x10s (haven’t measured) placed inbetwen those joists acting as individual rim joist between these joists. Then the joists from the interior of the house extend and land only on the stud wall. So there are two seperate joist systems that come together but not in a cohesive way at this stud wall, preventing a proper rim joist and allowing a significant amount of air leakage. (I’ve caulked a decent amount on the outside of these individual rim joist blocks to try and stop airflow here.) Further, the brick veneer on the outside of this wall has an air gap that vents right up into the rim joist and crawlspace area. So instead of placing the pieces used as a rim joist between the joists stopping at the stud wall, they placed them on top of where the brick veneer wall ends, seemingly fitting flush from the underside of the deck/ screenporch with where the brick veneer ends. Further, behind the brick veneer there seems to be osb or something similar, but there looks to be no housewrap or water membrane to prevent water getting directly onto the OSB.

I’m at a loss for where to start here and want to make sure i get this all sorted out. I’m having a spray foam estimate done tomorrow so I’ll see what he says but would still appreciate thoughts on how to best tackle this situation. I can upload pictures of everything if that would help.