Crawlspace vapor barrier
Zone 3 (Sacramento, CA), 1907 house with a crawlspace with a dirt floor, working to convert it to non-vented (conditioned) space. Open cell spray foam on the walls and rim joist. No signs of there ever being water in crawlspace. The grade inside and out is within a couple inches of even, and the poured concrete foundation wall is 4-8″ above grade. I plan to cover the dirt floor with 10 mil polyethylene sheet, taping the seams. Conventionally the guidance is to continue the plastic up the foundation wall and mechanically fasten it near the top. In this case, because of the short foundation and the need for a termite inspection gap, the attachment would be essentially at the floor/foundation corner. At that point, is mechanical fastening still necessary? Can I just run it up to the foundation and stop there? Vapor barrier effectiveness is a matter of net coverage, not perfection, right?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Bump
Keith,
Yes you are right. The only reason to seal the poly would be if radon was a concern, and running the poly up the wall serves no useful purpose.
> Vapor barrier effectiveness is a matter of net coverage, not perfection, right?
Only if you block airflow from one side of the barrier to the other. For example, turn the plastic edge downward and bury it - will stop most.
Thanks Jon, that's a good point.