Wall Vapor Barriers

A smart vapor retarder is a vapor retarder material with the unique ability to react to changes in relative humidity by altering its physical structure.

Wall vapor barriers.

Required tools for this polyethylene vapor barrier project. A vapor barrier reduces the movement of water vapor by. Air vapor barriers. The problem with vapor barriers the original reason for using vapor barriers was a good one.

Vapor barriers are also a cold climate artifact that have diffused into other climates more from ignorance than need. A smart vapor retarder is able to adapt its permeability to allow the wall to dry should moisture get trapped in the wall cavity. Fire resist products are formulated for burn resistance and have passed the nfpa 285 test in many wall assemblies. An excellent discussion about the differences between vapor barriers and air barriers can be found in quirrouette 1985.

A vapor barrier s job is to keep water vapor in humid air from diffusing through one side of a wall and finding a cool surface inside the wall. Building codes may require different details for termite control in your region. With fiber insulation and a vapor barrier moisture can get trapped in the insulation leading to moldy insulation and decay in the wood framing. In areas with high humidity such as greenhouses rooms with spas or swimming pools and bathrooms vapor barriers are often recommended.

How to use plastic as a vapor barrier in the walls. Think of a glass of ice water. The water vapor can come through the concrete from the soil or from indoor air that comes in contact with the concrete. The word barrier has the inference of a solid seal that would stop any moisture flow but these or any materials would let some vapor pass through.

Cap the interior of the foundation wall with a 6 mil layer of plastic and galvanized flashing both to block moisture and to serve as a termite barrier. To increase moisture barrier protection ccw also provides a variety of flashing products for use with air and vapor barrier systems. In practice we now understand that when vdrs are installed on the interior of an assembly they also prevent inward drying. Most authorities recommend vapor barriers in certain situations.

The history of cold climate vapor barriers itself is a story based more on personalities than physics. Vapor barriers are not actually barriers at all but vapor diffusion retardants or vdrs which at the molecular level balance the flow of moisture. Water vapor in the warmer air of your home begins to condense on the colder surface of the glass of water. When a vapor barrier is on the side of a wall where the dry air is i e outside in winter or inside in summer moisture problems can occur.

Avoid adding interior vapor barriers where the outer wall construction already includes a material with vapor barrier properties.