Insulating and sealing area between joints on perimeter of basement wall (rim joist?)

888

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I have a question about insulating the area between the joists at the outer perimeter of the basement wall (rim joints?). This is a poured basement wall with the 2 x 12" joists tied to a 2 x 12 resting on a maybe 2 x 6 or 2 x 8 sill plate on top of the poured basement wall, brick veneer over dimensional lumber walls with sheathing, typical build for that era in our area 1973/Ohio).

When we bought the house it had the original ratty fiberglass roll insulation above a drywall ceiling down there. I ended up pulling down the drywall ceiling to deal with the wiring issues created by the previous owner and plan on replacing the insulation as well. It's full of dust and mouse bits.

I noticed that the rim joist area was radiating cold, there was just fiberglass insulation in that area butted up against the outer board. I had some EPS (expanded polystyrene) sheets left from another project so I cut them to fit in these areas, and it helped immediately.

Thinking more about it, I wondered if I would create a moisture issue and I've seen some people use spray foam or other means to seal the edges of the EPS to keep humidity out from behind the EPS so it doesn't collect and create mold or rot the wood. I do run a dehumidifier down there full time to keep everything dry but I assume I still need to do something to seal the EPS?

If this is really necessary, I've got all kinds of permanent obstructions in the way of being accurate with applying sealant to those edges in a lot of places. Is it possible to pull the EPS back out, spray some kind of sealant onto the wood in that area to protect it from moisture, and then reinstall the EPS without the edge sealant?

Thanks in advance.
 

888

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Maybe something like this?

 

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