Attic Insulation Vapor Retarder

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.

Attic insulation vapor retarder.

If this is accomplished and a similar air infiltration retarder is installed in sidewalls mechanical ventilation such as a heat recovery ventilator should be installed to prevent trapping air pollutants and moisture within the house. Adding a second vapor barrier could cause condensation to become trapped in the insulation between the two vapor barriers. Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. Whether or not you need a vapor retarder hinges on three main factors your climate your home and the location of the wall you re insulating.

If installed in an attic a continuous vapor retarder is usually used to reduce air infiltration. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Sounds like a good idea but the vast majority of moisture problems are caused by air leakage not diffusion even in places like maine.

Moisture moves by two transport mechanism. Cima does not recommend the use of vapor barriers with cellulose insulation except in circumstances of exceptionally high moisture levels such as an indoor pool facility or very cold climates. Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days. A vapor barrier or vapor diffusion retarder is a material that reduces the rate at which water vapor can move through a material.

The older term vapor barrier is still used even though vapor diffusion retarder is more accurate. Do the air sealing. In any case the vapor barrier must point to the warm side. That s because cellulose is the only insulation that actually manages moisture.

To know if you need a vapor retarder ask yourself a few basic questions. 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. First the kraft paper is a vapor retarder meant to reduce the potential for moisture problems caused by diffusion. Stop worrying so much about vapor retarders.

Attic insulation should always be installed with the paper backing facing toward the living space the ceiling in this case. 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. Air movement and diffusion.