Attic Insulation Vapor Barrier Or Not

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.

Attic insulation vapor barrier or not.

Not every wall does. Fiberglass insulation must stay dry to be effective. I install my vapor barrier in the middle of the wall system between the two walls. Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. This acts as a barrier to keep heated moist air from rising up into the attic during cold weather. Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted. With an effective vapor barrier moisture will not affect your house.

Even if it asks you to. Attic insulation should always be installed with the paper backing facing toward the living space the ceiling in this case. 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. Vapor barriers in attics should only be installed on one side of the insulation.

The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days. Not be trapped inside. Never compress or fluff your insulation.

However all attics vented or unvented and in all climates should have an air barrier such as an airtight drywall ceiling. You can forego the plastic and use a vapor retarder kraft faced insulation or latex ceiling paint in all other climates except hot humid or hot dry climates. Such a location works both as a vapor barrier as well as an air barrier and eliminates the need for an external air barrier not a easy application on a multi storried building as well as any special electrical pans and their sealing. With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool.

By having a vapor barrier in your attic you prevent the seepage of moisture thus keeping all the surfaces that would remain covered by mold and mildew dry. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. 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. Since some leakage of moisture into the insulation in inevitable murphy s law you want it to be able to freely escape from the insulation into the attic.