I have an 80 y.o. bungalow in Chicago. Attic had no insulation, so went with an un-vented attic and had closed cell foam sprayed into the rafters. Sadly, I failed to have the top-plate foamed at the time. If I pull up the attic floorboards and foam the top plate between the joists from the inside, does this still leave the house vulnerable to stack effect from the exterior? Can I open the soffit and apply closed cell foam to the exterior (home is brick construction) at the location of the top plate, essentially "sandwiching" the plate in foam, and then restore the soffit? The sill plate is foamed in the basement.