Why is there condensation in between 1.5" polyiso board and roxul insulation?

Tyler Norrie
Updated: Feb. 12, 2021

Hi guys im from Canada and I recently finish studying and insulating my basement. I used one and a half inch polyiso board insulation glued to the wall with adhesive and I left a half inch Gap all around the board to spray foam. In front of the wall I frame to buy for walls and insulated with Roxul insulation Batts I went to go do some electrical work today and pulled back a bath and noticed that there was a bunch of condensation and a little bit of mold in between the bat and the polyiso. Did I do something wrong here? The humidity in my basement is 45%.

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