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No air should be allowed on the f.b./concrete joint. Air brings moisture form outside/inside (humidity). http://joneakes.com/jons-fixit-database/743 Foamboard installed air-tight to concrete will insulate and vapor retard any cold moisture coming through the concrete. If you air-seal the f.b. and glue as mentioned; with the "closed grid pattern" (horizontally and vertically) which limits the surface area of the air movement and wetness to diffuse through-- rather than drain-down to collect/pool at the bottom- possibly wetting wood framing (to mold, being organic) or cavity insulation from wicking- degrading it's R-value- if fiberglass; http://archive.nrc-cnrc.gc.ca/eng/ib...ling-heat.html

Seal the perimeter edges (canned foam) when installing against the closed-grid adhesive pattern. Mastic/tape the seams between panels, keep in mind f.b. will shrink over time (reason I typed mastic first); http://www.buildingscience.com/documents/published-articles/pa-foam-shrinks

Rim, as said already;
http://www.diychatroom.com/f103/insulating-rim-joist-caulk-spray-foam-around-edges-168849/

Gary
Thanks, Canucker, I was busy cut/paste my other links from other threads....!
 
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