No Vapor Barrier In Attic Insulation

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.

No vapor barrier in attic insulation. Foam blocks airflow needs no vapor barrier and has a higher r value per inch than loose fill or batts so you ll get more protection with less depth. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses. Experts say that if you are putting in a second layer of insulation you should have no vapor barrier between the two layers. Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted.

A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. Not every wall does. 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. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

Fiberglass insulation must stay dry to be effective. The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor. With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.

Then cover the foam with drywall as required for fire safety. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. The best approach for a vented attic in a cold climate is installing a layer of drywall with a good coat of latex paint the paint creates a semi permeable vapor barrier.