Foam Board Insulation Over Vapor Barrier

The previous owners went over the plaster lathe with 1.

Foam board insulation over vapor barrier.

However an installation between the studs can pose a challenge. If the wall cavity get wet for any reason then the wall will need to dry primarily to the interior. It s made of environmentally sound closed cell polyisocyanurate foam bonded to a durable white matte non glare aluminum facer and a reflective reinforced aluminum facer. R matte plus 3 thermasheath 3 is rigid foam plastic thermal insulation r matte plus 3 thermasheath 3 is rigid foam plastic thermal insulation board.

Over the years i ve come to rely on two approaches for basement insulation projects and remodelling including closed cell spray foam and closed cell xps foam board. Do no use a vapor barrier under the insulation. Although lstiburek talks about the risks of vapor barriers in the article he s really talking about the risks of interior polyethylene not vapor barriers. Cover the insulation with a vapor barrier before you install it.

2 don t use a vapor barrier such as poly on the interior. You don t want moist air leaking into the roof cavity. Seal the insulation or the ceiling surface below against air leakage. When installed in the correct thicknesses these to methods result in a proper vapor barrier and a superior insulation.

A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter. 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 s best to use only a class iii vapor retarder such as painted drywall. Use closed cell spray foam closed cell foam board extruded polystyrene such as dow styrofoam or foil faced iso board.

When installing the foam use caulk or tape for maximum insulation between the material and the board or floor. Many types of rigid foam including foil faced polyiso and faced eps are vapor barriers. Not every wall does. The goal is to keep the inside face of the foam sheathing above the dew point of the interior air.

All foam boards absorb water vapor. After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. Rigid foam insulation is usually a qualified vapor barrier. Keep foam board insulation away from direct sunlight prior to installation.

It will degrade its r value.