Home Vapor Barriers

Vapor Barriers

Crawlspace Vapor Barriers

Throughout the United States, even in desert areas, there is moisture in the ground from groundwater being absorbed. Even in an apparently dry crawlspace, a large amount of water is entering the home. In a dry crawlspace, the moisture is drying out as fast as it is entering, which causes high moisture levels in the crawlspace and elsewhere in the house. A solid vapor barrier is recommended in all crawlspaces and should be required if moisture problems exist.

This vapor barrier, if properly installed, also reduces the infiltration of radon gas. Of course, if the moisture is coming from above ground, a vapor barrier will collect and hold the moisture. Therefore, any above ground source of moisture must be found and eliminated. The source may be as obvious as sweating pipes, or may be more difficult to spot, such as condensation on surfaces. The solution can be as simple as applying insulation to exposed sections

of  the piping or complex enough to require power exhaust fans and the addition of insulation and vapor barriers.

The more common causes of moisture problems in a new home are moisture trapped within the structure during construction and a continuing source of excess moisture from the basement, crawlspace, or slab. To resolve this potential problem, 6-mil plastic sheets should be laid as vapor barriers over the entire crawlspace floor. The sheets should overlap each other by at least 6 inches and should be taped in place. The plastic should extend up the perimeter walls by about 6 inches. The plastic sheets should be attached to the interior walls of the crawlspace with mastic or batten strips. All of the perimeter walls should be insulated, and insulation should be between the joists at the top of the walls. Vents, which may need to be opened in the late spring and closed in the fall, should not be blocked. If not properly managed, moisture originating in the crawlspace can cause problems with wood flooring and create many biological threats to health and property. A properly placed vapor barrier can prevent or reduce problem moisture from entering the home.

Concrete paints, waterproofing sealers, or cement coatings are a temporary fix. They ***** or peel and cannot stop gases, such as water vapor and radon.

Damp basement air spreads mold and radon through the house. Efflorescence (white powder stains) and musty odors are telltale signs of moisture problems. Basement remodeling traps invisible water vapor, causing mold and mildew.

Most basements start leaking within 10 to 15 years. The basement walls and floors should be sealed and preserved before they deteriorate. The basement floor should be concrete which has been poured on at least 6 inches of gravel. The gravel distributes groundwater movement under the concrete floor, reducing the possibility of the water penetrating the floor. A water proof membrane, such as plastic sheeting, should be laid before the concrete is poured, for additional protection against flooding and infiltration of radon and other gases.The basement floor should be gradually but uniformly sloped in all directions toward a drain or a series of drains. These drains will permit the basement to drain if it becomes flooded.

Water or moisture marks on the floor and walls are signs of ineffective waterproofing or moisture proofing. Cellar doors, hatchways, and basement windows should be weather-tight and rodent-proof. A hatchway can be inspected by standing at the lower portion with the doors closed; if daylight can be seen, the door needs to be sealed or repaired.

Vapor Barriers for Concrete Slab Homes

Strip flooring and related products should be protected from moisture migration by a slab. Proper on-grade or above-grade construction requires that a vapor barrier be placed beneath the slab. Moisture tests should be done to determine the suitability of the slab before installing wood products. A vapor barrier equivalent to 4- or 6-mil polyethylene should be installed on top of the slab to further protect the wood products and the residents of the home.

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