Crawl Space Plastic. When?

At what stage in the construction process should the plastic be put down. This is a single fam. residence. House is dried in, (except for a front door) and the insulation guy wants to wait but it's very humid under there (located in Central alabama) and some joists look moldy. I've read on some sites that say ASAP and others to wait longer. Any thoughts?
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I'm a builder in Birmingham, and I have my framers put the vapor barrier down on their first day. That way no one has to crawl around to install it, and I can be sure no framing lumber gets left under it for termite bait.
It doesn't have to go in at that time, however.
If you have hardwood floors going in, its best to have the vapor barrier in a few weeks before that installation as the moisture can affect its installation.
You should have at least 24" from the ground to the bottom of your floor joist, and 18" from the ground to any girders.
It is likely that the mold came on the joist as they have a lot of moisture in them and they have been sitting on a lumber yard or in a warehouse for a while.
Shannon Pate ASP Home Building, Inc.

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on 9/24/2007 9:44 PM snipped-for-privacy@yahoo.com said the following:

There should be, to prevent rot and mildew, which apparently has already started. If there are vents, perhaps using a fan blowing into the space until the vapor barrier is put down will help.
--

Bill
In Hamptonburgh, NY
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On Sep 24, 9:44 pm, snipped-for-privacy@yahoo.com wrote:

Check the moisture in the ground, the amount of vent area, then visit The Building Science Corporation web site. My preferance, assuming adequate venting and no unusual levels of soil moisture, would be to put down 6 mil or better poly with edges lapped and fastened to the masonry NOW. Cover it with a couple of inches of sand and hope the insulator doesn't make a mess of it. The Habitat for Humanity houses I've designed put down the poly early with good results over 10 years. T
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