Do you live in a cold climate? Then you know the importance of insulation, but have you given sufficient thought to vapor barriers?
As an integral part of an effective home insulation strategy, a vapor barrier (also known as moisture barrier and vapor retarder) has a double role to play:
1. It controls air movement, or air infiltration, through the walls.
In other words, it keeps your costly heated air from escaping to the outdoors.
2. It prevents the formation of condensation within the walls.
Condensation takes place when the warm inside air meets a cold surface - much like a glass of ice water on a hot day.
This has the following beneficial effects, some immediate and some long-term:
your home's comfort level improves due to the lack of cold drafts;
your home's energy efficiency is increased noticeably;
your heating costs go down substantially;
your house's building materials (wood, insulation, drywall) are protected against moisture, molds and mildew, which are the quickest source of deterioration;
your family's health is safeguarded against the disastrous effects of molds.
Vapor Barrier Types
Most types of vapor barriers can only be installed in new construction or during major remodeling or renovation projects. They are:
1. Polyethylene plastic, which comes in rolls of various widths and lengths and an average gauge of 6 mil (or 0.15 millimeters). This is the most common type, and in cold climates it's installed on the inside of the wall, between the insulation and the drywall. The cost is very reasonable and quickly amortized thanks to the energy savings realized.
Any old plastic just will NOT do. The material used must have the proper government approvals and fire ratings clearly visible.
2. Treated paper (or foil) bonded to batt insulation. This has a limited effectiveness due to the difficulty in obtaining a proper seal at the edges and joints.
3. Foil insulation (also known as radiant barrier) is an excellent vapor barrier and it also adds some R value to your existing insulation.
4. Black polyethylene. The black color is due to an ultraviolet inhibitor. This type is for use on the outside, in hot, humid climates where air cooling, rather than heating, is the norm.
5. Cross-laminated or fiber-reinforced polyethylene. These high-density specialty products are used where higher strength is required, such as a retrofit over rough, irregular surfaces, or under rugged handling conditions.
The cost is quite a bit higher than regular polyethylene vapor barrier products.
6. Exterior plywood and aluminum foil are also used as vapor barriers.
Vapor Barrier Installation
The main principle which must be observed when installing a vapor barrier, is that it absolutely must be continuous, that is to say, each section must be tightly sealed to the one next to it, as in wall to wall, wall to ceiling, etc., using special tape and acoustic sealant which is applied with a caulking gun.
The vapor retardant material must also be sealed to all protrusions and penetrations such as pipes and electrical boxes. Any break in the seal will result is warm air escaping through it, which would defeat the purpose.
Foil insulation/vapor barrier is installed a bit differently from polyethylene sheets: edges must not overlap, and special aluminum tape must be used. Also, in order to be effective as a reflective material, air spaces must be created on the foil side.
And If You're Not Remodeling...
...consider vapor retarder paints. These are relatively new on the market, they are inexpensive and can be used on previously painted surfaces. They come in the form of a latex primer that has a vapor "perm rating" of 0.45 to 0.7 (whereas 6 mil polyethylene sheet has a perm rating of.06).
The smaller the number, the better, so that the 6 mil poly is almost eight times as effective as the paint. However, anything less than 1 perm is considered to be a vapor retarder and that's why vapor retarder paint qualifies.
Get Professional Advice
Not every type of vapor barrier goes with every type of house structure, kind of insulation or wall material, and it's not within the scope of this article to recommend exactly which one is the right one for your circumstances. Its purpose is to make you aware of the possible need for a vapor barrier to get the maximum benefit from your home insulation strategy.
Therefore, you should get expert advice before undertaking your vapor barrier installation.
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