frost inside wall
 

So i insulated a north facing/exterior 2x4 wall with mineral wool this fall. No issues. I put drywall up, but it hasn't been mudded/taped yet. I noticed an air leak around an outlet switch so i pulled a piece off to see what the deal was. In the process i noticed frost on the clapboard (exterior sheathing)..not a horrible amt, but enough to make the wool freeze to the sheathing. The sheathing is covered by tar paper and the siding. Should be worried? I checked the next 2 bays and the same thing so its not just the one bay with the leaky outlet. Is it because the wall isn't completely finished (moisture seeping through the joints?...

It has been 0F'ish or lower for the past 3 to 4 days...so very cold.

Dealing with moisture in winter sucks. My house is very dry. The basement was showing like mid 30% humidity the other day. We run bathroom vents.

As long as you don't have a vapor barrier sandwich inside the wall somewhere, frost on the outside of the envelope is not a bad thing. In winter, it is better to have outdoor air finding its way in, as cold outdoor air has less moisture in it.

Somewhere inside the wall, there will be a plane where it is at freezing temperature. Whenever possible, this plane should be inside of free air or space occupied by insulating material. Any moisture that freezes at that plane should have a path in or out when winter is over. Since you have exterior clapboards or lap siding, they should be able to breathe enough to let the vapor out once it warms up.

Ok.. I'm not going to worry too much about it. I'll try to get everything finished up soon which should help air/moisture leakage even more.

Where my air leaking for the outlet was where the wire had penetrated the exterior sheathing (outdoor light) and then the top plate..i never sealed either hole..so i sealed those so i hope that cuts some air flow in the wall down.