Where Does The Polyethylene Vapor Barrier Go On A Roof

There are three classes of vapor retarders.

Where does the polyethylene vapor barrier go on a roof.

A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. Single ply membrane perm rating 0 03 0 06. A vapor barrier better described as a vapor retarder reduces the amount of water vapor entering your wall and ceiling cavities. Typically a vapor retarder has to have a perm rating of 1 0 or less to be successful.

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. Built up roofing membrane perm rating 0 00 0 02. In any case the vapor barrier must point to the warm side. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one.

The lower the perm rating the less diffusion i e less drying occurs through a material. An introduction to vapour barriers and vapour retarders. 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. Some air barriers are vapor open and allow moisture to escape.

Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer. Do not confuse vapor retarders with air barriers. Class i impermeable vapor proof 0 1 perm. Plastic vapor barriers should only be installed in vented attics in climates with more than 8 000 heating degree days.

In circumstances where conditions inside a home or office are much different than outdoor conditions water. In hot humid climates attics should not be vented and vapor. 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. Everyone knows that water in roof systems is never a positive.

What is a vapour barrier. This barrier is meant to keep moisture from getting to the insulation in the walls and ceilings and it is required by building codes when insulating most houses. Most authorities now agree that vapor barriers are important under certain conditions but not necessarily as a whole house solution for every home. Not every wall does.

The process of water vapor passing through building materials is called vapor diffusion is it a vapor retarder or an air barrier. Resolution of the vapor barrier debate.