Attic Vapor Retarder

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.

Attic vapor retarder.

The ability of a material to retard the diffusion of water vapor is measured in units known as perms or. The older term vapor barrier is still used even though vapor diffusion retarder is more accurate. 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. Attic vapor barrier detail for cold climates.

Zone 5 zone 6 and zone 7 require a class ii or lower vapor retarder on the interior surface of insulation in unvented insulated roof or attic assemblies and the condensing surface shall be maintained above the dew point temperature of the interior air. It lets wall cavities dry out to help prevent mold. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. If your climate does not meet these conditions a vapor retarder like latex ceiling paint will work well for your house if you are in all other climates except the hot dry and hot humid.

Some regions don t require a vapor barrier. 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. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. A vapor barrier or vapor diffusion retarder is a material that reduces the rate at which water vapor can move through a material.

Whether using loose fill or batts put the vapor barrier closest to the warm side of your installation where hot moist air would get in facing the house s interior in cold climates beneath floor insulation and the attic s interior in hot climates on top of floor insulation. A plastic vapor barrier is best installed in a vented attic within climates with over 8 000 heating degree days. Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. In summer when humidity is high it increases permeability so that moisture can escape as air tightness is maintained.