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Embedded Joists & Top of wall detail

user_6270056 | Posted in General Questions on

Hello,  I have 2 areas/questions on insulating the rim joist and basement on my house. House was built in 1960 and is located in zone 7a in Canada.

1) Rim Joist insulating:
I have been trying to find a way to air seal and possibly insulate the rim joist area where the joists are embedded into the concrete wall with out causing rot and moisture issues within the joist seat. My research has come to 2 possible solutions.  (Rim joist area is about 2′ above ground)
Option A. The joist is simply caulked to the concrete wall while the gap at the top is foam sealed.  See image attached. From what i have read this option should work.
Option B. is to include a piece of 1″ XPS in the rim area.  With this option i am wondering if the XPS is thin enough to avoid the issues in the joist seat?
(I know there are other options like exterior insul, as well the idea of cutting the joists off and bearing on new walls.  both of these options are not practical for my current situation)

2) Existing insulated walls:
I have existing insulated 2×4 walls with poly VB, the wall is spaced about 1/2″ from the concrete wall and the top of the framed wall is not sealed. During the winter (below freezing) frost is accumulating against the concrete wall. I believe this is happening due to air leakage because the top of the wall is not air sealed.  I am thinking if i seal the top of the wall with spray foam as per the attached image this should help reduce the amount of frost on the concrete wall?  But would this also create an issue for trapping moisture within the stud cavity that I would be better off leaving open?
I would very much like to leave the existing walls/insul as they are as there doesn’t appear to be any mold issues.

Thank you

GBA Prime

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