Glossy paints are generally more effective vapor retarders than flat paints, and acrylic paints are generally better than latex paints. To be a good vapor retarder, it should consist of a relatively high percent of solids and thickness in application. The paint formula usually indicates the percent of pigment. If the perm rating of the paint is not indicated on the label, find the paint formula. "Vapor barrier" paints can be an effective option for existing homes in colder climates. Your home may not need a more effective vapor retarder than the numerous layers of paint on its walls and ceilings unless you live in extreme northern climates. Obtaining an energy assessment and thoroughly sealing any leaks it reveals is are very effective for slowing moisture movement in and out of your home. How, where, and whether you need a vapor retarder depends on the climate and the construction of your home.Įxcept for extensive remodeling projects, it's difficult to add materials like sheet plastic as a vapor retarder to an existing home. Vapor retarders can help control moisture in:Įffective moisture control in these areas and throughout a home must also include air-sealing gaps in the structure, not just the use of a vapor retarder. Unfaced expanded or extruded polystyreneĬlass III vapor retarders (greater than 1.0 perms and less than or equal to 10 perms):.
#Water barrier code#
The International Residential Code describes three classes of water vapor retarders:Ĭlass I vapor retarders (0.1 perms or less):Ĭlass II vapor retarders (greater than 0.1 perms and less than or equal to 1.0 perms): The ability of a material to retard the diffusion of water vapor is measured in units known as "perms" or permeability. The older term "vapor barrier" is still used even though "vapor retarder" is more accurate. A vapor retarder is a material that reduces the rate at which water vapor can move through a material. climates, vapor barriers, or - more accurately - vapor diffusion retarders (vapor retarders), should be part of a moisture control strategy for a home.
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