Plywood walls and Vapor Barrier
Hello,
I just had insulation installed in my steel building. They put the insulation in, then the WMP vapor barrier on top all the way down to the floor.
I am looking to install some plywood for my walls and was wondering if I should cut the WMP down first or is it ok to leave it up and right against the plywood? I am up in the Pacific Northwest, if that's a factor.
Thanks!
Guidelines have changed, depending on climate in the area
Quote:
Originally Posted by
Evan Lentz
Thanks everyone, I'll check into it with Lamtec just to be sure. I feel like there may be some exceptions as Peter mentioned. Just want to do it right the first time!
The Oak Ridge National Laboratory has a building research division. (I did some modeling for one of their experimental buildings.) About 20 years ago I asked about vapor barriers. I was told the previous guidelines to install a vapor barrier on the inside of the wall cavity is good for cold climates. In the south where air conditioning is used to cool for much of the year the problem is the warm outside moisture will work through the outer wall and can condense on the vapor barrier and cause the insulation to get wet, lowering the efficiency and likely causing problems with mold inside the walls. At the time they suggested vapor barriers on both sides of the insulation. I see a different recommendation now:
From this Dept of Energy document, https://web.ornl.gov/sci/buildings/d...heet-2008.pdf:
"If the outside air is hot and humid, then moisture from outside will try to diffuse through the walls toward the dry, air-conditioned inside air. We used to tell people to install vapor retarders to try and stop this moisture diffusion. But we have learned that if moisture moves both ways for significant parts of the year, you're better off not using a vapor retarder in the walls at all."
It might be helpful to contact ORNL and ask. Their mandate is to help everyone who asks. I don't know how to contact the right person now but you can probably get it from the ORNL web site or call the information number.
JKJ