Where to install the vapor barrier for a finished basement?

Replies to This Discussion

Permalink Reply by Chris Peters on March 11, 2011 at 12:22pm

I'm referencing Joe Lstiburk's "Cold Climates" You should not install poly on the walls in the assembly. It will cause the wall to retain moisture. The key is to let the walls dry to the inside or the outside. I would also not use fiberglass in the basement because it is hydrophilic. A water resistant insulation would be a better material to use. I recommend you get a copy of "Cold Climates" it covers all the different areas in a house and the best methods for building and insulating.

• ▶ Reply

Permalink Reply by Jim Klebes on March 11, 2011 at 3:12pm

Thanks Chris for your feedback. I will get Joe Lstiburk's book so I can add it to my reference library. 

• ▶ Reply

Permalink Reply by Chris Peters on March 11, 2011 at 9:15pm

You're very welcome.

• ▶ Reply

Permalink Reply by Don Hynek on March 19, 2011 at 10:01am

Also, review the work of the Pat Huelman and the folks of the Cold Climate Housing Center. Pat and his people have done a lot of work in this area. And he and Dick Stone do a lot of training -- Affordable Comfort, the Duluth EDC conference, etc.

 

I don't believe any of their work contradicts the info in the "Builder's Guide: Cold Climates" book. But they may well have info on the most recent "miracle" materials out there intended to "allow" building assemblies that will just never work. (Like this goofy idea that you can successfully put a functioning vapor barrier on the warm side of a below-grade concrete wall!) 

• ▶ Reply

Permalink Reply by Jim Klebes on March 19, 2011 at 10:10am

Thanks Don for making me aware of Pat Huelman group. I'll definetly review their findings.

• ▶ Reply

Permalink Reply by Albert Schinazi on March 22, 2011 at 4:07pm

Jim,

Your question and the subsequent responses got me thinking. 

I tell myself I should know the answer to this question but I found myself wavering a bit.

I have “Cold Climates” but it has been awhile since I have reviewed it and looked at this wall profile.

 

Out of curiosity I searched the web and here is what I found at an EPA site.

http://www.epa.gov/indoorairplus/technical/moisture/1_12.html

 

“An appropriate assembly for the inside of a basement wall consists of 1 in. of plastic foam board or closed-cell polyurethane spray foam followed by a stud wall with fiberglass insulation filling the cavities. This assembly is covered with moisture- and mold-resistant gypsum board covered by two coats of latex paint. The foam board serves two purposes: providing a capillary break between the foundation wall and the stud wall and keeping warm, humid basement air away from the earth-chilled foundation. It is good practice to put 1 in. of foam board beneath the sole plate of the stud wall and the basement floor and to leave a ½-in. gap between the basement floor and the bottom of the gypsum board. Doing so provides protection from minor floods and damp concrete floors.”

 

Clicking the link provides additional explanation and context for this strategy.

I wonder if this is consistent with the other resources mentioned. If not i would like to hear others thoughts.

• ▶ Reply

Permalink Reply by Ken Watts on January 25, 2013 at 8:22am

You can find an excellent publication on this question at http://www.buildingscience.com/documents/reports/rr-1003-building-a....  The publication presents many solutions and rates them on several criteria.  They also conducted detailed thermal and moisture modeling.

I put 2" XPS on my basement walls as a temporary way to add some insulation before I got to the task of finishing the basement walls. I did not seal the joints between the sheets or the gaps at the top and bottom of the sheets.  I had lots of ice on the top of the foundation wall and ice at every joint and gap down to the soil line.  A well sealed vapor barrier at the foundation wall is absolutely critical to preventing moisture problems.

After seeing the moisture/ice problems first hand, I think I will insulate the stud walls with closed cell foam to assure that I have no air leaks.  This will cost more but the peace of mind is worth it.  I live in a very cold climate near Yellowstone National Park.  We have had many consecutive days of -20 to -30 F this winter.  I am sure this contributed the ice formation behind the XPS and on top of the foundation wall.

• ▶ Reply