Vapor Barrier For Attic Thickness

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.

Vapor barrier for attic thickness.

If you are going to use fiberglass i d recommend unfaced with 6 mil or thicker clear plastic as a minimum. However americover recommends 10 mil or higher for crawl space applications. Americover offers thicknesses all the way up to 20 mil. In many of those cases vapor barrier paint woks better than installing sheeting.

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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. Resolution of the vapor barrier debate. The kraft facing is a vapor barrier as well but only when properly installed which it rarely is.

The other thing you should look for when choosing a vapor barrier product is how that barrier is constructed. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. Codes for residential applications often cite a 6 mil 0 006 inch thick minimum reinforced poly vapor barrier. Instead of pulling away the insulation sheets to slip in the barriers apply at least one thick coat maybe two to the insulation.

A mil is equal to 0 001 inch of thickness. We recommend using a vapor barrier of 16 mil or higher. Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer. In answer to your question you need to have a vapor barrier between the insulation and the interior.

Plastic specifically 6 mil polyethylene plastic is. Avoidance of the installation of vapor barriers such as polyethylene vapor barriers foil faced batt insulation and reflective radiant barrier foil insulation on the interior of air conditioned assemblies a practice that has been linked with moldy buildings lstiburek 2002. Without a vapor barrier in place condensation inside the walls could ruin the insulation and promote the growth of harmful mold and bacteria. 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.

In circumstances where conditions inside a home or office are much different than outdoor conditions water. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective.