Basement Insulation With XPS
I've been doing my basement remodel over the past month. I have XPS insulation completely sealed on the block wall. I also took out the fiberglass insulation in the rim joists and put 2" XPS insulation in and then sealed with foam. After this I tossed the fiberglass insulation back in. Now a month later I have all of my framing completed. However, I read that fiberglass should be kept out of the basement. So I took out all of my fiberglass insulation in the rim joists to leave the XPS exposed. I have I think around 70-80 rim joist spaces. After I pulled all of the fiberglass insulation out to be tossed away I noticed 2 of the XPS boards had a small bit of sweat towards the top. I cut into the XPS and everything seams fine... just a surface sweat. It evaporated an hour after the fiberglass was out. It may have been that it wasn't sealed correctly and air was coming in.
My question... I would really like to put Roxul R-15 Stone insulation in front of that XPS board in the rim joist. To add a little more insulation R value and for fire safety. Will this eventually cause all the XPS boards to sweat? Obviously with the Roxul insulation in front of the XPS... the XPS will be cooler on both sides. I just don't want to trap moisture between where the XPS meets the Roxul insulation. I'm not sure how warm or cool it would be behind the Roxul.