Fiberglass insulation must stay dry to be effective.
No vapor barrier in attic insulation.
Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted.
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.
So for this top layer you would be purchasing unfaced insulation batts not rolls of an r value of at least 30.
The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below.
Not every wall does.
The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor.
Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.
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 paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.
Then cover the foam with drywall as required for fire safety.
Vapor barrier up or down.
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.
Experts say that if you are putting in a second layer of insulation you should have no vapor barrier between the two layers.
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.
A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.
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.