What is the best rigid foam insulation for the exterior of a foundation under a deck?
I live in Calgary, Alberta and bought a house built in 2007. I noticed this past winter when I started renovating my basement that the rim joists were poorly insulated and we're damp. I insulated the rim joists with R10 rigid board with spray filling the gaps and then R12 batt insulation. I then noticed that under our front deck, the hole for the foundation wasn't back filled so approximately 4 feet of concrete was left exposed with the sil plate.
I'm thinking of taking Rigid board and installing it against the concrete wall and will plate to hopefully help with preventing dampness and further heat loss. Is this recommended? Do I need to put a protective barrier over the rigid board, or will leaving it exposed once it's secure to the foundation wall be enough? The porch is covered and has skirting so the rigid board is somewhat protected from the elements.
Any help/advice is appreciated