Frost behind insulation in basement??

Old 01-24-11, 08:05 AM
Thread Starter
Join Date: Oct 2010
Location: usa
Posts: 10
Upvotes: 0
Received 0 Upvotes on 0 Posts
Frost behind insulation in basement??

One foundation wall in my basement is constructed of 2x6 studs with wood on the outside. The wall is completely above ground. When i bought the house, all the stud cavities had in them was r-19 insulation. I noticed yesterday that there is frost all over the wood. The frost is between the wood and the insulation. It is currently 15 degrees outside and 65 degrees in the basement. What is the appropriate way to attack this issue? I have read many differing opinions. No mold is noticeable yet. Should i replace the insulation and then put a 6 mil plastic over it? I have read dos and don'ts about plastic between insulation and drywall and can't figure which way is correct. Whatever i do, i want to test it and see if it works before I drywall.

Thanks for any feedback.
Old 01-24-11, 08:36 AM
Join Date: Oct 2008
Location: New England
Posts: 9,460
Received 47 Upvotes on 43 Posts
A vapor barrier should be avoided when it is blocking the only path for moisture to be dissipated. That situation is usually below grade. Above grade, any moisture should be able to pass to the outside. So, VB on the inside above grade is ok. As for fiberglass against a concrete wall, I'm not a fan of that, but as long as there is no moisture you should be ok. Make sure you read up on insulating and air sealing the rim joist before you close thing sin.

Old 01-24-11, 04:38 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Posts: 27,132
Received 1,924 Upvotes on 1,728 Posts
Yeah the frost occured because of there not being an air barrier and vapor barrier between the 65F and the 15F. Kraft facing just doesn't block enough air and water vapor to prevent frost. And no drywall means air could freely pass through the fiberglass.

So I'd also say a poly VB would be good on that wall, followed by drywall. If you have outlets in the wall, you can spray foam behind them (between the sheathing and the back of the box) since they are also a prime spot for air leakage. Air leakage when you have temperature differences like that will cause a lot of ice within the wall.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: