No Vapor Barrier In Attic Insulation

Then cover the foam with drywall as required for fire safety.

No vapor barrier in attic insulation.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Vapor barrier up or down. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

Experts say that if you are putting in a second layer of insulation you should have no vapor barrier between the two layers. 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. With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool. The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor.

Fiberglass insulation must stay dry to be effective. Not every wall does. Hi beth 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. Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted.

The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. So for this top layer you would be purchasing unfaced insulation batts not rolls of an r value of at least 30.