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Why Use Vapor Barriers

25 May 2010

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In cold climates, insulation alone is not enough to keep our costly heat from escaping. Given the slightest opportunity our precious heat will find its way out in an alarming way.

Once we understand the principle that warm air is attracted to cold air, and not the other way around, it should become almost a matter of pride to keep that warm air in!  Although some heat is lost by conduction through the insulation, most of the heat loss in a building is through air movement, or air infiltration, through the walls.

That's where vapor barriers come in. A vapor barrier – also known as vapor retarder – is merely a continuous sheet of impermeable material installed on the inside, i.e. the warm side of the wall, and it's designed to keep the warm air from escaping through or around the insulation and other building components.

There are several reasons for wanting to keep the warm air inside the house through a vapor barrier installation; among them:

  • Energy efficiency
  • Heating costs
  • Preventing the deterioration of the building materials (wood, insulation) by moisture (hence the alternate term moisture barrier). In winter, as the heated air meets the cold air, it creates condensation, which is water of course. The vapor barrier is designed to prevent this phenomenon from taking place.
  • Health problems caused by molds