Which way does foil face on insulation?

I have an old house that was prefab (&#;s). The walls are plywood inside and out with what appear to be furring strip material used as studs. Every  37&#; there is a metal strip about 4&#; wide that runs the entire height of the wall inside and out with more fur strips under the metal for strength. These metal enclosures also were areas to run electric throughout the house. I believe all of the furring strips were nailed and glued and the plywood as well. They really didn&#;t insulate the walls other than some kind of spray that looks like possible sprayed tar on the plywood between the wall. I would like to insulate a small portion of the external wall about 10&#; long. I would like to use foam board on the interior side of the wall glued to the interior plywood and then fur on top of the foam insulation and finally drywall over that.  The foam board I purchased has a foil face on one side. I am not sure if the foil facing should face inside or to outside. What I am concerned with is the foil facing going to create moisture in the wall?  I would appreciate any advice!! Thanks so much! (Location St. Louis, Missouri)
Thanks again,
pbt109

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Correct me if I&#;m wrong, but shouldn&#;t the foil facing on polyiso face the interior in climate zone 5 to help retain heat? It will be used on basement rim joists. The heating season is obviously longer than the cooling season.

Furthermore, should I leave an air gap between the foam and the wood or should I place the foam directly against the wood before spray foaming the perimeter?

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Lastly, should I seal the perimeter of the rim joists with the one part foam prior to installing the rigid foam and spraying around the perimeter of that?

I was thinking of not sealing the perimeter prior to installing the rigid foam to give any moisture entering the cavity an avenue to escape. Although no moisture should really be entering the cavity from the inside and to the best of my knowledge, polyiso is vapor-impermeable (not sure about the 1 part foam but I think it is vapor-permeable).

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