Hello, my basement rim joists are insulated with vermiculite loose fill insulation, I believe it’s original to the house that was built in the 50’s. Climate zone 6/7 in the US so very cold. I’m not too worried about the asbestos potential as it’s encapsulated by a 2×8 on the interior. I don’t want to disturb it either. My plan was to add rigid foam to the rim joist but upon further investigation I found it was already insulated. The Rigid foam I planned on using was John manville’s CI max polyiso with aluminum facer because it’s fire rated for leaving exposed. 

My question is should I still add rigid foam or not? I’m worried if I cover it with foam any potential moisture getting in wouldn’t dry to the interior anymore. Add in that vermiculite is used in gardening for its moisture holding properties. I also want to eventually do exterior insulation, probably foam EPS panels which would cover the rim joist area from the outside. 

How should I handle this without removing the vermiculite? 

Thanks