Attic Vapor Retarder

The ability of a material to retard the diffusion of water vapor is measured in units known as perms or.

Attic vapor retarder.

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. In summer when humidity is high it increases permeability so that moisture can escape as air tightness is maintained. Even though we apply vapor barriers to exterior insulated walls in cold climates it s no longer recommended for ceilings floor of the attic. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it.

Because it s nearly impossible to seal penetrations in the ceiling the reality is water vapor will get into the attic. If installed in an attic a continuous vapor retarder is usually used to reduce air infiltration. 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. Some regions don t require a vapor barrier.

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. 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. Attic vapor barrier detail for cold climates. 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.

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. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. The older term vapor barrier is still used even though vapor diffusion retarder is more accurate. A vapor barrier or vapor diffusion retarder is a material that reduces the rate at which water vapor can move through a material.