No Vapour Barrier In Attic

Thus installing vapor barriers on wall surfaces must.

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. By the time you paint the drywall though you. To stop the movement of vapor effectively through air leaks your vapor barrier should also have an air barrier such as an airtight. Returning to the original question about whether you need a class i vapor retarder i e a vapor barrier if you re getting almost no water vapor diffusing through something that s not a vapor retarder at all i think the answer is clear.

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. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

Attic vapor barrier detail for cold climates. Do not add a vapor barrier on top of the insulation in your attic since the paper facing on the existing insulation is the vapor barrier. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.