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.

Vapor barrier for attic thickness.

Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer. Most authorities now agree that vapor barriers are important under certain conditions but not necessarily as a whole house solution for every home. A vapor barrier in an attic assembly in a severely cold climate with the absence of an air barrier will likely be ineffective. 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.

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. The other thing you should look for when choosing a vapor barrier product is how that barrier is constructed. Codes for residential applications often cite a 6 mil 0 006 inch thick minimum reinforced poly vapor barrier. Americover offers thicknesses all the way up to 20 mil.

A mil is equal to 0 001 inch of thickness. However americover recommends 10 mil or higher for crawl space applications. This translates into a permeance rate of only 0015 this is considered impermeable in american building codes. Without a vapor barrier in place condensation inside the walls could ruin the insulation and promote the growth of harmful mold and bacteria.

Instead of pulling away the insulation sheets to slip in the barriers apply at least one thick coat maybe two to the insulation. The paper facing contains a layer of impermeable asphalt that prevents water vapor from passing through it. The kraft facing is a vapor barrier as well but only when properly installed which it rarely is. The application can vary so read all instructions on your specific brand of paint.

In answer to your question you need to have a vapor barrier between the insulation and the interior. 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. The insulation fiberglass or cellulose is then placed on top of the drywall with no vapor barrier above or below. In circumstances where conditions inside a home or office are much different than outdoor conditions water.

We recommend using a vapor barrier of 16 mil or higher. Resolution of the vapor barrier debate.