Vapour Barrier Attic Insulation

When adding additional insulation to an attic that is already insulated never use insulation with a vapor barrier.

Vapour barrier attic insulation.

Now with attic insulation heat is no longer lost from the living space such that moisture may remain trapped in the attic vapor barriers were therefore necessary to reduce moisture flow into the attic. If you do there is a chance that moisture that has slipped by the first vapor barrier will become trapped by the second vapor barrier decreasing the value of your insulation. During the energy crisis of the 1970s a prevailing belief took root where it was thought that tightly sealing walls and ceilings with a vapor barrier was essential to blocking heat transference and reducing energy costs it was soon determined however that unless the seal was absolute moisture that did get into sealed walls could create serious structural problems and health issues such as. 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.

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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Not every wall does. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.

The heat being lost from the house below warmed up the attic so that moisture was lost through the vents as vapor. 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. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.

In any case the vapor barrier must point to the warm side. Attic vapor barrier detail for cold climates 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.