Insulating rim joists
I’ve read a few articles on insulating the rim joist and the general recommendation seems to be to insulate the rim joist with spray foam or foam board. That said, I always see a few comments that recommend against this as it caused sill plate rot, mold, etc.
The home is in Missouri and was built in 2006. Regular batt insulation was stuff in the rim joist and the few areas of the basement that were finished they placed batt insulation and framing directly against the concrete wall (three rooms in the basement are “conditioned”). When I removed the framing and insulation I found no evidence of wetness or mold and we do not currently have any signs of water coming in the basement for the past 5 years. We also run a dehumidifier in the basement shooting for 50% humidity. I do see a foam gasket between the sill plate and concrete wall and to my knowledge the only thing on the outside basement wall is that black water sealer.
My plan is to caulk the rim joist, then use 2″ Owens Corning foam board (r10) and expanding foam to seal/insualte the rim joists. I will also use 2″ foam board on the walls, then frame and drywall.
Has anyone in Missouri had issues with insulating this way where it ended up causing mold to get trapped between the foam board and rim joist? Will I have any issues with water vapor from the concrete wall going up and transferring to the rim to cause rot? Any thoughts or insights would be appreciated.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part