Attic Insulation Vapor Barrier Or Not

I install my vapor barrier in the middle of the wall system between the two walls.

Attic insulation vapor barrier or not.

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. Not every wall does. 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. 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.

After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. 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. Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. Never compress or fluff your insulation.

Protects your attic from mildew and mold such fungi thrive in damp places. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. This acts as a barrier to keep heated moist air from rising up into the attic during cold weather. However all attics vented or unvented and in all climates should have an air barrier such as an airtight drywall ceiling.

Vapor barriers in attics should only be installed on one side of the insulation. 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. Fiberglass insulation must stay dry to be effective. 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.

Before the introduction of attic insulation attics in cold climates were poorly insulated and plastic ceiling vapor barriers were omitted. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Attic insulation should always be installed with the paper backing facing toward the living space the ceiling in this case. 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. Not be trapped inside. Then cover the foam with drywall as required for fire safety. With spray foam unlike with loose fill or batts you must cover the soffit vents they aren t needed to keep the roof cool.