Crawl Space Vapor Barrier

Crawl Space Vapor BarrierA crawl space vapor barrier is an essential component of waterproofing your crawlspace that aims to keep moisture out of your crawlspace and ultimately out of your home. A vapor barrier is designed to prevent the movement of moisture from one area to another. The vapor barrier is a physical barrier that must be continuous and free of gaps to work properly. Crawl space vapor barriers not only can help keep moisture out of your crawl space and home, they help to insulate better and can save you on heating/cooling costs.


Before beginning the installation, you want to ensure that your crawlspace is free from standing water or mold. If these items are not corrected before installation of your vapor barrier, they continue to worsen and cause you to have to remove your vapor barrier at a later date in order to correct the issue.

A crawl space vapor barrier should be made of at least 6-7mil thick polyethylene with some systems even as thick as 20mil. The vapor barrier should be placed across the entire floor of the crawlspace with 1 to 2 foot overlaps between sheets. This should span the entire width of the crawl space and continue up the foundation walls from approximately 6 to 12 inches. Pieces should be firmly taped together to ensure that there are no gaps in coverage. You can also add up to 2″ of fine sand over the vapor barrier to help keep the sheeting in place and prevent air circulation from moving it around. In addition you can install a vapor barrier on the underside of the floor joists to provide additional insulation.

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