Attic Insulation Vapor Barrier Or Not

Fiberglass insulation must stay dry to be effective.

Attic insulation vapor barrier or not.

This acts as a barrier to keep heated moist air from rising up into the attic during cold weather. 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. Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. 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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Even if it asks you to.

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. However all attics vented or unvented and in all climates should have an air barrier such as an airtight drywall ceiling. I install my vapor barrier in the middle of the wall system between the two walls. 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 are sheets of plastic or other material placed on one side of insulation sheets. With an effective vapor barrier moisture will not affect your house. Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. 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.

With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool. Not be trapped inside. 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. Protects your attic from mildew and mold such fungi thrive in damp places.

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. Then cover the foam with drywall as required for fire safety. Vapor barriers in attics should only be installed on one side of the insulation. Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted.