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Vapor Barriers
Vapor barriers are a great source of misunderstanding and incorrect information. This confusion is centered on vapor barriers vs. vapor retarder. EcoFoil offers an insulation vapor barrier that can be used for both insulation and a vapor barrier. But first, in order to fully understand the distinction between a vapor barrier or a vapor retarder, it is important to understand the meaning of permeability and how it is measured.
Permeability is the measure of the amount of water vapor, in other words moisture, which can pass through a given material in a certain span of time. The unit of this measurement is expressed by the term “perm”. For example, a Class I Vapor Retarder has a perm of 0.1 or less. The lower the perm number the less permeable the substance is.
While there is no recognized industry standard for testing permeability, the American Society for Testing and Materials (ASTM) has developed a method for testing permeability that is widely used by many companies. The classification for this test is ASTM-E96-00 Standard Test for Water Vapor Transmission of Materials.
There are several variations of the test procedure which vary upon the suspected permeability of the given sample. It is important to note here not all testing methods will produce the same results, and that these test results may not accurately represent the product will perform in the field.
A very basic summary of the test is as follows. A container filled with water is placed on one side of the material in question. On the other side of this membrane there is another container. One test method places a desiccant in the empty container. The weight of each container is measured over a period of time to monitor any changes. The transfer of weight from one container to another would show that there has been movement of water vapor.
The term vapor barrier is technically incorrect, rather, what we are referring to are vapor retarders. These membranes designed to keep out, or at least restrict the movement of water and water vapor. They are separated in to three classes.
A Class I Vapor Retarder is one that has a perm rating of 0.1 or less. This is the only level of vapor retarder that is considered impermeable, a true vapor barrier. A polyethylene vapor barrier is an example of a Class I Vapor Retarder (as you will find with EcoFoil's insulation vapor barrier material)
A Class II Vapor Retarder is one that has a perm rating up to 1.0 and greater than 0.1. This class is considered semi-impermeable. Kraft faced fiberglass batt is an example of a Class II Vapor Retarder.
A Class III Vapor Fetarder is one that has a perm rating up to 10 and greater than 1.0. This class is considered semi-permeable. Drywall painted with one coat of latex paint is considered a Class III Vapor Retarder.
Any material with a perm rating above 10 is considered permeable.
In 2006 the US Department of Energy adopted the International Residential Code (IRC) and the International Energy Conservation Code (IECC) which divides North America in to 7 climate zones. Each climate zone has its own set of building codes. Which class of vapor retarder is right for your needs would not only depend on which zone you are building in, but it would also be influenced by the method of construction and the structure’s intended use. The combined variables in selecting the proper vapor retarder far outweigh the scope of this article.
Now that you have a clearer understanding of vapor retarders you can make more informed choices when planning your building project.
EcoFoil's reflective foil insulation, including radiant barrier and bubble insulation, work as a product for insulation, vapor barrier, and even a rodent barrier. It is technically an insulation vapor retarder. Insulation with vapor barrier capabilities serves dual purposes saving costs for your project. An aluminum foil vapor barrier is commonly used in the following instances:
- crawl space vapor barrier
- basement vapor barrier
- concrete vapor barrier
- floor vapor barrier
- wall vapor barrier
- metal roof vapor barrier
- vapor barrier underlayment
- bathroom insulation vapor barrier
Depending on the project you are taking on, vapor barrier insulation can be an important part of ensuring long term stability and a dry structure.
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