Should You Put Plastic Under Your House in the Crawl Space?

Plastic sheeting, also called a vapor barrier or a moisture barrier, is often installed in crawl spaces to help keep moisture out of a home. If you are experiencing moisture problems, often indicated by the growth of molds or a musty smell, consider installing a vapor barrier in your crawl space.

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The same plastic sheeting that keeps moisture in greenhouses keeps it out of your home.

Moisture Problems

Excess moisture can cause a host of problems inside your home. Ground moisture evaporating up through a crawl space and into the sub-floor above can cause hardwood floors to rot and vinyl sheeting to peel. Excess moisture can also cause paint and wallpaper to peel, increasing the likelihood of insect infestation, or produce mold and mildew growth. Mold and mildew growth is perhaps the most serious of these problems because exposure to mold and mildew can result in significant health problems, including eye irritation, asthma attacks, and other respiratory problems. A vapor barrier can help abate this spread of moisture on your home's interior.

Vapor Barrier Types

Vapor barriers are made from several different materials, the most common being polyethylene plastic and roofing paper. For crawl spaces, choose a vapor barrier with a permeability value of 1.0 or less. The best materials for crawl spaces include polyethylene plastic and asphalt-laminated paper.

Installation

Vapor barriers should be laid directly on the floor of the crawl space to stop moisture from coming in at its source--the ground. If you have hardwood floors above the crawl space, install the vapor barrier over 2/3 of the crawl space floor; this proportion keeps the majority of moisture away but lets enough in to prevent the hardwood from drying out. For carpet or vinyl floors, lay the vapor barrier across the entire crawl space floor. Once the vapor barrier has been laid, use electrical tape to secure the sheets together. Finally, consider spreading a 1- to 2-inch layer of gravel on top of the vapor barrier. This helps prevent condensation and wear and tear from shifting.

Additional Solutions

Installing a vapor barrier is only one way of controlling moisture. Other measures include running a dehumidifier to keep the relative humidity inside your home between 30 and 50 percent, installing ventilation ports, storm windows, and insulation, managing external water so that it drains away from the home, and reducing moisture-generating activities inside the home.