No Vapour Barrier In Attic

The science of moisture movement.

No vapour barrier in attic.

On the other hand an air barrier a properly detailed air tight drywall ceiling for example in the absence of a vapor barrier can be effective since it stops the flow of vapor laden air. No you don t need a vapor retarder class i or otherwise. Water vapor can pass through building materials in several ways including direct transmission and by heat transfer but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps including cracks around electrical fixtures and outlets and gaps along baseboards. Now with attic insulation heat is no longer lost from the living space such that moisture may remain trapped in the attic vapor barriers were therefore necessary to reduce moisture flow into the attic.

To stop the movement of vapor effectively through air leaks your vapor barrier should also have an air barrier such as an airtight. Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic. Attic vapor barrier detail for cold climates.

By the time you paint the drywall though you. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.