Foam Board Insulation Over Vapor Barrier
Not every wall does.
Foam board insulation over vapor barrier. You don t want moist air leaking into the roof cavity. When installing the foam use caulk or tape for maximum insulation between the material and the board or floor. If the wall cavity get wet for any reason then the wall will need to dry primarily to the interior. 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.
After the insulation is in place you will want to add a vapor retarder sometimes called a vapor barrier if you need one. 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. However an installation between the studs can pose a challenge. However an installation between the studs can pose a challenge.
It will degrade its r value. All foam boards absorb water vapor. Cover the insulation with a vapor barrier before you install it. The goal is to keep the inside face of the foam sheathing above the dew point of the interior air.
2 don t use a vapor barrier such as poly on the interior. Unfortunately the language in the joe lstiburek article that you linked to is imprecise. When installed in the correct thicknesses these to methods result in a proper vapor barrier and a superior 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.
Use closed cell spray foam closed cell foam board extruded polystyrene such as dow styrofoam or foil faced iso board. Seal the insulation or the ceiling surface below against air leakage. It s best to use only a class iii vapor retarder such as painted drywall. A vapor retarder is a material used to prevent water vapor from diffusing into the wall ceiling or floor during the cold winter.
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. Keep foam board insulation away from direct sunlight prior to installation. Insulation radiant and vapor barriers rigid foam board over fiberglass i have an 80 year old house in upstate ny with a very drafty kitchen. Do no use a vapor barrier under the insulation.
The previous owners went over the plaster lathe with 1.