You may be familiar with more obvious moisture problems due to damaged roofs and walls or rainwater runoff that seeps into foundations or up through concrete foundation floors. However, crawl spaces are also prone to moisture problems from water vapor that rises from the ground and gets trapped in the enclosed space. Fortunately, you can add plastic sheeting as a water vapor barrier to correct the problem or prevent it from occurring.
What Is a Vapor Barrier?
A vapor barrier slows down ground moisture from affecting a house sitting above it. The barrier is made of rolls of ordinary sheet plastic that are laid down on the ground in a crawl space to trap water in the ground from evaporating or condensing. The U.S. Department of Energy calls a vapor barrier a "vapor diffusion retarder" since plastic sheeting, even with seams sealed, cannot seal off 100 percent of the moisture.
The plastic sheeting is made of reinforced polyethylene plastic sheeting (poly) in various thicknesses and strengths, usually from 6 mils to 23 mils, depending on your budget and needs. A mil is equal to 0.001 inches of thickness, so a 6-mil sheet is (0.006-inch thick). A 6-mil sheet is considered a Class 1 vapor retarder, which is the minimum recommended thickness when installing a reinforced poly vapor barrier.
Vapor barrier sheeting can cost 15 cents to $1.50 per square foot; the cost variation is based on the thickness of the sheet. For an expert to install, it can run $2,000 to $4,000, depending on the space size and sheet used.
Benefits of Installing a Vapor Barrier
A vapor barrier is a relatively inexpensive remedy to a situation that can get out of control if left unchecked. With so many benefits, installing a vapor barrier in a crawl space seems a great option for homeowners, and it has many distinct advantages:
- Keeps moisture from seeping up through the flooring into your home
- Holds off mold and mildew from growing
- Reduces potential for structural wood rot
- Discourages pests that prefer wet environments
- Prevents wiring mishaps caused by moisture or rust and corrosion of wires and connectors
- Provides extra insulation to improve a home's energy efficiency
- Gives cleaner, easier access to the crawl space
Problems Caused by Moisture
Moisture is one of the main foes of a home's structure—potentially causing structural problems. Uncontrolled moisture can cause rot and decay in wood framing and other materials, fostering mold and mildew.1 Moisture is most damaging in a crawl space because you often can't see it.
Moisture determines if a home, room addition, or below-grade flooring is even possible. If moisture is a known problem, vapor barriers can be integrated into wall, ceiling, and floor construction to combat moisture affecting the home.
Mold and Mildew
One of the most serious problems caused by moisture is mold, mildew, and other fungi.2 Eliminating mold is complex, and fully remediating mold-related problems is expensive. Mold can blacken floor cavity insulation and structural elements. Because there is often no light and minimal ventilation in a crawl space, the problem only goes away with preventive measures or remediation.
Rot
Structural elements of your house, such as joists, sills, posts, and beams, are wood. Wood will rot when it comes into contact with water for prolonged periods.
Rodents and Other Vermin
Many types of animals are drawn to water and can invade your home. These pests include carpenter ants, termites, rats, mice, snakes—even skunks and armadillos.3
Do You Need a Vapor Barrier for Your Crawl Space?
While a vapor barrier is not required, it is highly recommended as many crawl spaces are prone to moisture. A vapor barrier can also reduce pests, insects, and potential structural damage to your home that comes from too much moisture.
I ordered this vapor barrier to cover a spot in my crawlspace space that was lightly damp. This was easy enough to put in place, the hardest part was me getting under the house. The vapor barrier has a white side and black side. I wasn't sure if it mattered which one is up so I went with white up like their picture on the packaging. If I need more material I would certainly buy this one again.
I used the vapor control under my 1950 home craw space. Easy to cut , strong and looks great covering up the dirt. No more musty smells and condensation. The vapor control is designed for easy cutting and provides strong protection. Its visually appealing design effectively covers dirt, eliminating musty smells and condensation.
This vapor barrier is pretty thick and you will probably need help managing it. We also ordered the landscape stakes with the black, plastic tops. That helped with keeping the plastic secure. Overall, we are very happy with the vapor barrier.
Excellent poly film if you need somethingthick like 10 mil. Opaque, one side black, one side white. Used for vapor barrier. Much better quality than big box store rolls.
Wasn't expecting for it to be as thick as it was but yes very good product especially as i needed it for moisture barrier under my house. The product's thickness exceeded my expectations, making it an excellent choice for use as a moisture barrier under my house.
