Insulation for Rim Joist Sitting Directly on Hollow Concrete Block – GreenBuildingAdvisor

Hello,

I have a 100 year old house in climate zone 6B.  It costs a pretty penny to heat and am gradually trying to improve the efficiency of the house.  I have already air sealed the attic and improved upon the insulation up there.  The walls were insulated with cellulose at some point, but I know that some stud bays don’t have any insulation.

I want to insulate my rim joist using pieces of 2″ rigid foam with spray foam around the perimeter.  Then add mineral wool for additional insulation.  This seemed like a great plan, but upon more investigation I found that the concrete blocks that the rim joist is resting on (no sill plate) are hollow.  There is a decent amount of air that is moving through the blocks.

I am concerned if I spray foam the blocks, then that might cause issues with moisture within the blocks.  Has anyone run into a similar situation?  I have asked around my neighborhood at what other homes have, but most homes have no insulation.

Thank you,

Evan