Insulating Rim Joist with Mixed Exterior Cladding – GreenBuildingAdvisor

Hello,

I am attempting to properly insulate the rim joists in our basement prior to finishing the walls, however I am unsure of how to proceed due to the mixture of cladding and exterior detailing. I am in zone 5a, Columbus, Ohio and the house was built in 1992 with a full concrete block foundation.  The exterior is brick and stucco. The brick walls are brick, OSB, 2×4 framing, fiberglass insulation, polyethylene and drywall.  The stucco portion is on 3 sides of the house and consists of traditional 3 coat stucco, 1” thick blue Dow foam board (I think R-3), 2×4 framing, fiberglass insulation, polyethylene and drywall.  

The current rim joists have unfaced fiberglass insulation in all bays.  My original plan was to do 2” XPS, spray foam the perimeter, followed with R-15 Rockwool. due to the 1” XPS on the exterior stucco portion, I am concerned I will make a foam sandwich. I know the 1” exterior foam isn’t enough to properly insulate the Rim joists, but due to the type of cladding it is not feasible to remove it and add more exterior insulation. I wasn’t sure if I should do one of the following or something else:

I had planned to use 1.5” XPS in two layers with seams taped for the walls, 2×4 framing and 1/2” drywall. There is a sill gasket between the concrete blocks and the sill plate. I have already caulked the perimeter of all of the joist bays. 

Thank you in advance for your help. 

Amanda