A vapor barrier is an essential part of the moisture control strategy for a home or building.
A vapor barrier (moisture barrier) refers to any material that prevents moisture from passing through the walls or roof of a building. This material can be plastic or better yet, Prodex Total Insulation - 13/64 inch, 5mm closed cell polyethylene foam covered on both sides with .0012-inch (00.03mm) aluminum foil facing. Prodex Total Insulation (Vapor Barrier, Class 1. perm<0.1 ) also provides R-value 16 and a radiant barrier. Prodex Reviews
Permeability (perms) refers to the measure of the rate of transfer of water vapor through a material. The lower the perm, the fewer the vapor that can pass through. Look for a vapor barrier with a perm of less than 1. Transmission rates are established by standard test methods. One common set of units is g/m²/day. or g/100in²/day. (1.0 US perm = 1.0 grain/square-foot·hour- inch of mercury ≈ 57 SI perm = 57 ng/s·m2·Pa).
Vapor barrier in a steel building
Condensation can be more significant problem in a steel building than temperature control. Moisture from condensation, rain and ground can create several problems in metal buildings. First, the presence or water or ice in the insulation seriously degrades both the thermal performance and service life of fiberglass, paper, wool and other traditional insulation materials. Second, water in contact with steel contributes to corrosion and lowers the service life of the building. Third, collection of water can lead to dripping, staining, mold, mildew and odors. All of the problems can be solved with properly installed vapor barrier insulation. Even in only moderately humid climates, condensation can cause serious problems in an unprotected steel building.
A building vapor barrier must be continuous to work - no holes, leaks, un-taped seams or edges. Leakage will negate the effectiveness of the barrier. Any tears, openings, or punctures that may occur during construction must be completely sealed with tape. Ending the vapor barrier at the floor or ceiling junction has the same effect as a large hole. To create the vapor barrier, the seam between the ceiling and wall must be sealed well. Think of your house as a large balloon with the vapor barrier as the skin of the balloon. A leaky barrier is not better than no barrier at all. .
Electrical boxes and plumbing lines will compromise the barrier if the edges are not sealed completely with tape. To maintain the integrity of the barrier, some builders nail 2" x 4" or 2" x 6" horizontal furring strips to the studs after the barrier is in place to make a channel for wiring and drain lines. Drywall is nailed over the furring.
- Wood strapping (airspace)
- Prodex Total Insulation (vapor barrier)
- Outside finishing
Prodex Total Insulation will keep heat and moisture in during the winter. It will not absorb moisture in the event of a water leak. If you are finishing your basement, install Prodex Total Insulation (vapor barrier) on the basement walls before framing.
A vapor barrier is needed on the ground under the house (on top of the dirt in the crawlspace) to prevent the framing from getting wet. A vapor barrier should also be used under a slab-on-grade foundation or poured cement basement floor. Since a damp basement is one of the greatest producers of moisture (up to 50 lbs/day of vapor), the vapor barrier under concrete floor slabs and over earth floored crawlspaces are integral structural components of interior moisture control.
Vapor barriers in warm and cold climates
In the Southeast, where cooling and high humidity are the primary concerns, a vapor movement would tend to be from the outside to the inside of the building. Here, the vapor barrier should be installed on the exterior as a whole house wrap.
A vapor barrier is critically important in northern climates where there is a large difference between the indoor and outdoor temperatures. The most important place to install a vapor barrier in cold climates is between the warm interior house wall and the wall cavity insulation. If no water vapor can diffuse into the wall cavities, no condensation can occur.
Prodex Fast Action, (vapor barrier) doubles as cavity wall insulation and radiant barrier. This insulation vapor barrier can help you meet the DOE insulation recommendations for new homes for both the building cavity wall (R-11 to 13) and the basement interior wall (R-11). This will replace the older practice of wrapping the interior, exterior and basement walls in 4 or 6 mil polyethylene sheeting as a vapor barrier.
Through the process of convection, movement of air will always be from warmer areas to cooler areas. This means that in winter, the warm, moist air inside your house is constantly trying to escape to the colder air outside. Warm air will hold more moisture than cold air.
As this warm air expands, it will naturally move to the cooler areas of your wall cavities, crawl space and attic. When the air cools, it will contract and lose moisture causing condensation in these spaces. A vapor barrier acts as a physical shield to repel moisture. As most attics are vented, a vapor barrier is not required under the attic floor mass insulation although it may be advisable in more humid climates.
The primary purpose of a vapor barrier is to keep moisture from getting inside your walls. Condensation within the walls can cause wood rot, mold, mildew, and fungus growth. Signs of condensation within the walls include blistering exterior paint and mildew stains on the walls or ceiling in areas where there is no plumbing.
Prodex Total Insulation: Vapor Barrier: Class 1. perm<0.1 Eliminates condensation
July 16, 2012