Insulating Below-Grade Walls
I know there is a lot of information on this website, and elsewhere, but for some reason I cannot get a definite answer on this. I live in Edmonton, Alberta Canada and I am in the process of finishing my basement, and decided to remove all the insulation from the rim joists and frost wall (it was fibreglass with polyethylene vapor barrier). The rim joist were so poorly sealed, and the poly had rips and tears everywhere. My joists are TJI’s and are very difficult to seal.
I install Halo Interra, https://buildwithhalo.com/halo-interra/, it is a XPS infused with graphite, and comes with a built in vapor barrier. It is currently installed throughout my walls, taped or foamed in between boards. I have also installed it in the rim joists and tied it into the walls. I have decided to replace my existing steel stud framing with wood stud framing, and the existing fibreglass with 6″ mineral wool (R22). My question around all this is once this is all completed, do I need a vapor barrier, vapor retarder, or just air tight drywall? I am concerned about putting a vapor barrier / retarder and having moisture trapped between the two barriers. I am also concerned that if I do not put the barrier in, I might get condensation build-up on the foam board, either on the walls or the rim joists or both.
Any advice would be greatly appreciated. I was looking at Siga Majrex as a smart vapor retarder, but want to make sure that it is required before investing all that money. Also, is it worth changing the steel stud framing to wood framing? I read that steel stud framing can cause a lot of thermal bridging reducing your R-value drastically. Also, I was considering installed 1″ of foam board below the wood bottom plate (if I go this route), to reduce thermal bridging.
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