Should I add a vapor barrier in this situation


I'm finishing my basement. I am wondering about the north wall which is a 2×6 stud wall (walkout basement). I removed the fiberglass insulation an put 2 layers of 3/4" rigid insulation (sealed edges with silicone)… each has a R4. I will then put the fiberglass back. I am wondering about putting the plastic vapor barrier back. I don't khow how permeable the rigid insulation is and I don't want to trap moisture in the wall. It was -10 below last night and I didn't have any condensation on the rigid insulation. ( I haven't put back the fiberglass yet).The rigid insulation sealed up all the leaking seams and eliminated all the drafts.

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Best Answer

Foam board, especially the one in your pics, act as a vapor barrier. The only issue with it is when you cut it and install between joists or studs. Then it needs to be taped, caulked, or foamed. You said you caulked them so you have completed your air seal. Adding another vapor barrier will only cause moisture problems and wood rot. I have been insulating homes for over 30 years and have seen the entire sides of homes that have had to be tore out and rebuilt because of the second vapor barrier.