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Handyman Q&A

Crawl Space Vapor Barrier Will Prevent Pests and Rot


Question: The sandy soil of the crawl space below my house is usually moist and downright wet during the rainy season. When a termite exterminator was treating my house, he placed a plastic sheet over most of the space but not all of it. Is this adequate?

Answer: The sandy floor of the crawl space should be covered with a vapor barrier of polyethylene plastic sheet, 4 to 6 milliliters thick. This reduces moisture in the space, and the potential for rot in wood framing. Dry conditions also reduce termite and carpenter ant activity.

The vapor barrier must cover the entire floor, and joints between sheets should be taped closed with heavy-duty plastic tape. The vapor barrier should extend to the foundation wall and be taped to it.

Reduce crawl space moisture by ensuring gutters and downspouts discharge water away from the house and that the ground slopes away from the house on all sides.

Further, there should be at least two vents--one each at opposite sides of the foundation. The vents are sized as follows: 1 square foot of unobstructed vent area for each 1,500 square feet of crawl space floor.


To submit a question, write to Popular Mechanics, Reader Service Bureau, 224 W. 57th St., New York, NY 10019.

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