Vapor Barrier For Attic Walls Thickness

Attic vapor barrier detail for cold climates.

Vapor barrier for attic walls thickness.

My question is should iuse a vapor barrier inthe attic floor. Whether or not you need a vapor retarder hinges on three main factors. But if it does the barrier should face inside in northern heating climates and outside in humid southern climates. Plastic specifically 6 mil polyethylene plastic is.

I want to install insulation in my attic floor which i use for storage. Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic. In any case the vapor barrier must point to the warm side. Concrete block with interior frame wall cavity insulation and brick or stone veneer applicability limited to mixed humid hot humid mixed dry hot dry and marine regions should not be used in cold very cold and subarctic.

Vapor barriers sheets of plastic or kraft paper keep water vapor out of the wall cavity so the insulation stays dry. The previous owner has 1 foam insulation with a a plastic vapor barrier only on the rafters of the roof about4 from the slate roof but not on the walls of the attic. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective. This wall assembly will dry from the vapor barrier inwards and will dry from the vapor barrier outwards.

Not every type of insulation needs a 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. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets.

Not every wall does. The science of moisture movement. 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. Water vapor can pass through building materials in several ways including direct transmission and by heat transfer but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps including cracks around electrical fixtures and outlets and gaps along baseboards.

Without a vapor barrier in place condensation inside the walls could ruin the insulation and promote the growth of harmful mold and bacteria.