Vapor Barrier Over Rigid Foam Insulation

All foam boards absorb water vapor.

Vapor barrier over rigid foam insulation.

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. 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. In circumstances where conditions inside a home or office are much different than outdoor conditions water. Keep foam board insulation away from direct sunlight prior to installation.

Not every wall does. In any case the vapor barrier must point to the warm side. To complete the vapor barrier you would want to foam seal or tape all the sides where the rigid meets timber because these gaps will facilitate vapor flow. It will also allow shorter fasteners to be used and no guesswork about stud locations when installing the new insulation and wall coverings.

When installing the foam use caulk or tape for maximum insulation between the material and the board or floor. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Resolution of the vapor barrier debate. It goes without saying that the holes would not be a good thing.

By installing the crawl space vapor barrier over the insulation you will prevent holes in the vapor barrier from securing the rigid foam to the wall. The rigid foam will not absorb moisture. This will not only eliminate the double air vapour barrier issue it will allow for additional thickness of rigid foam insulation to be installed improving the energy efficiency even more. Rigid foam insulation is usually a qualified vapor barrier.

However please be aware that spray foam is not the same as rigid foam. However an installation between the studs can pose a challenge. Cover the insulation with a vapor barrier before you install it. However an installation between the studs can pose a challenge.

Most authorities now agree that vapor barriers are important under certain conditions but not necessarily as a whole house solution for every home. Some debate still occurs over how necessary vapor barriers are but a consensus is growing closer.