No Vapour Barrier In Attic

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.

No vapour barrier in 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. Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. 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.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. 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. 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. To stop the movement of vapor effectively through air leaks your vapor barrier should also have an air barrier such as an airtight.

By the time you paint the drywall though you. The science of moisture movement. No you don t need a vapor retarder class i or otherwise.