Where Does The Polyethlene Vapor Barrier Go On A Roof

In most locations that means installing vapor retarders on the interior side of the walls and ceilings.

Where does the polyethlene vapor barrier go on a roof.

Vapor barriers are sheets of plastic or other material placed on one side of insulation sheets. 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. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful. 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.

This eliminates the need for a separate air barrier that could potentially prevent the moisture from escaping. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Everyone knows that water in roof systems is never a positive. In very cold climates the use of polyethylene plastic vapor barriers between insulation and interior wallboard may be beneficial provided all air gaps into any wall and ceiling cavities are also blocked.

Not every wall does. A vapor retarder is a material or system that is designed as part of the roof system to substantially reduce the movement of water vapor into the roof system where it can condense. For example the national roofing contractors association nrca recommends vapour barriers on the interior side of a roof in any climate where the outside average january temperature is below 40 f 4 c degrees and the expected interior winter relative humidity is 45 percent or greater. However if the inside of the structure is refrigerated as in a cold storage warehouse or food processing plant vapor barriers may be more effective on the outside of the wall or ceiling assembly.

In any case the vapor barrier must point to the warm side. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.