Where to install the vapor barrier for a finished basement?

I have an audit customer that is in the process of finishing his basement. The basement foundation walls are poured concrete. He has installed a polyethylene vapor barrier over the concrete wall per his brother's instructions who is a builder. He plans to install unfaced insulation in the 2 by 4 stud walls that are 2 inches away from the concrete wall. He will be also installing drywall and heating the space with his existing HVAC unit. This is an all-electric two story home located in Ohio.

 

I'm already recommending he seal the entire rim joist with foam since they are leaking a lot of air. The rim joists are currently fitted with faced fiberglass batts. My thoughts are to advise him to also foam the entire basement wall but I'm not sure this is the correct or the best solution. If he decides to install fiberglass batt insulation in the 2 by 4 walls, where should the vapor barrier be installed? The poured cement basement walls are dry with good drainage outside so I'm thinking the vapor barrier should be installed between the drywall and insulation since the basement will be a conditioned space.

Views: 59944

Reply to This

Replies to This Discussion

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

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!) 

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

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.

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.

polyethylene vapor barrier is the most common that the contractors use. See this http://www.agmrenovations.com/safebasement/ incase you need any information

No first-hand experience, but that stuff looks like spray-on bulk water proofing material not moisture seal. And why are they spraying it on after the stud wall was erected and not before?

Since he's also in Ohio and has a great deal of experience, you might want to reach out to Nate Adams at Energy Smart Home Performance for his opinion.

RSS

Forum Discussions

When is it too windy to use blower door?

Started by Brandon Walton in General Forum. Last reply by Don Hynek 14 minutes ago. 11 Replies

Electro Magnetic Fields (EMF)

Started by Barry L NewDelman in General Forum. Last reply by Arnie Katz on Thursday. 2 Replies

Affordable Housing Funding

Started by SUZETT MOFFITT in General Forum. Last reply by Diane Chojnowski Jul 19. 4 Replies

Latest Activity

Don Hynek replied to Brandon Walton's discussion When is it too windy to use blower door?
"You did a pretty good job -- there are a few tricks of the trade that might have improved precision…"
14 minutes ago
Profile IconBryan Magnuson and Rodney Bailey joined Home Energy Pros
4 hours ago
Laurie DiDonato updated an event

Hybrid HERS Rater Training September 2017 (NH) at Online/ Classroom in Manchester, NH

September 11, 2017 at 9am to October 6, 2017 at 5pm
EARLY BIRD DISCOUNT: Register by August 15th and get $200 off!This training has been approved by…See More
22 hours ago
Profile IconEmily Rhea, Spray-on Foam and Keith Flores joined Home Energy Pros
Friday

Photos

Loading…
  • Add Photos
  • View All

© 2017   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service