# Rigid foam up to subfloor on basement wall. What to do behind it?



## Gary in WA (Mar 11, 2009)

Fiberglass batts are OK (as you already have the best one between cold/warm now), Roxul is better- if only from a sound control/wetting performance. I would leave a small air gap between the two insulations or add minimal fibrous batt tight to the FB. The more cavity fill (in front of the foamboard) the colder the FB will be. You would be slowing the heat reaching the inside face of the FB= colder FB= more chance of condensation as it lowers the dew-point there,* Fig. 4*; http://www.buildingscience.com/docu...ld-weather-condensation-using-insulation/view

Did you cover the top of concrete wall against the mudsill plate?

Gary


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