Vapor Barrier in Crawl Space


Old 07-21-05, 06:24 AM
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Question Vapor Barrier in Crawl Space

I recently replaced a section of waste pipe. Unfortunately the pipe was under a crawl space that has a very rough "rat coating" of concrete (about two inches thick), which had to be partially removed. I now have a trench about three feet wide, twenty feet long, and two feet deep exposing the underlying soil. (The trench is at least six feet from the foundation walls). Through the approximately one square foot vent from the crawl space into the rest of the basement there is now a slight odor of damp soil. I tried stretching a thick polyethylene vapor barrier over the trench (like Saran wrap stretched over a bowl). However, because of the roughness of the concrete, there was no way that I could make a tight seal between the vapor barrier and the concrete floor. Instead I used broken pieces of the concrete (from the original plumbing job) as weights around the edge of the plastic to hold the vapor barrier in place. I have two questions: 1) Is this sufficient, because clearly there are gaps that will allow the moisture to enter the crawl space, and 2) Is there a potential health risk because organisms that may grow under the barrier now have an escape route into the house?
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Old 07-21-05, 07:46 AM
Join Date: Jul 2005
Location: Ottawa, Canada
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This is insufficient to fix the problem. Why wouldn't you fill in the trench with concrete?

With the escape of moisture in the crawl space, it will lead to mold growth in this area.
Old 07-21-05, 08:38 AM
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I have avoided filling in the trench with concrete and/or soil because I didn't think it was a good idea to re-entomb the waste pipes. (Getting to the waste pipes under the crawl space was a major job). Someone had suggested having the polyethylene vapor barrier follow the contour of the trench (rather than stretched over the top of the trench), and then covering it with a thin layer of small stones. Is this an improvement over the current method?

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