The facing of the insulation serves as a vapor barrier. Vapor barriers resist moisture penetration, keeping humid interior air from reaching cold surfaces where it could condense. In cold climates, vapor barriers go on the warm side of insulation. In hot, humid climates, they go on the exterior side.
Please note that the proper way to install it is to have it installed facing outward or towards the person installing it. Attic specialists look to install it facing downward on your ceiling. Meanwhile, when you're installing it in your crawl spaces, install the insulation facing upward.
Direction Matters: The vapor barrier should always face the warm side of your insulation. In the UK, that's usually the inside of your building.
When installing fiberglass insulation in your home, be sure to put the paper or foil vapor barrier facing toward the heated and cooled living area of the home (down in attics, up under floors, in on walls) to prevent condensation from occurring.
In climates that are hot and humid, a vapor barrier should be installed on the warm side (for walls, this would be just beneath the exterior cladding, over the insulation). For very cold climates, the warm side is the interior, so the insulation should have a vapor barrier separating it from the interior wall.
Therefore, when installing foil faced insulation always fit the foil side where the temperature difference is greatest. So, any time you use a single side foil insulation, the foil needs to be facing toward the living space.
Begin at one side of the crawl space and lay down 6-mil or thicker polyethylene plastic over the entire crawl space. Cut the sheets to size, allowing 6 inches or more along walls. Overlap the seams by no less than 12 inches and secure them together with the poly PVC tape.
The first is stapling Original AtticFoil to the bottom of the roof rafters via the Staple Up Method. The second is laying SuperPerf™ AtticFoil® out on top of the existing attic floor insulation like a blanket. Alternate methods like the Flat Top and the Hybrid are just modifications of the standard Staple Up method.
Add a vapour barrier on the warm side of the wall within the first third of the thermal resistance value of the overall wall insulation.
In Most Cases, Attic Insulation Does Not Need To Provide A Vapor Barrier. The good news is that blown-in insulation should not need a vapor barrier. Blown-in is primarily used on the attic floor, and vapor barriers are not a concern for attics in our climate zone.
Our view is that for mixed climates (aka heating dominated climate zones) the best place for a smart vapor barrier is inboard of the insulation because it will prevent conditioned air from entering the insulation layer and really help minimize or eliminate condensation.
You can use faced or unfaced batting when installing between the roof rafters of finished attic spaces. When using paper or plastic batting insulation, that moisture barrier should face outward toward the attic space. Even if the attic space is unheated, it's typically warmer than the outside air in winter.
Vapor Barriers
The facing of the insulation serves as a vapor barrier. Vapor barriers resist moisture penetration, keeping humid interior air from reaching cold surfaces where it could condense. In cold climates, vapor barriers go on the warm side of insulation. In hot, humid climates, they go on the exterior side.
Radiant barriers that are reflective on one or both sides may be used with any of these locations. However, if the radiant barrier is reflective on only one side, the reflective side must face toward the main attic space for Locations 1 and 5.
Alternatively, you can place one radiant barrier above your attic ceiling insulation and a second one below to maximize the beneficial effects in both summer and winter. Whichever approach you choose, don't allow any dust to accumulate on top of the reflective surface during the installation.
Vapor barrier materials are installed on the warm side of the insulation in a building assembly, as determined by climatic conditions. In warm climates, it will be on the exterior and in cold climates, it will be on the interior.
(The general rule for insulation is that the facing always goes toward the conditioned space.)
More than likely, installing an additional layer of poly over kraft facing won't cause any problems — it's no more risky than if the wall had only unfaced batts and poly — and the risk of using poly on the interior is relatively low in a cold climate like New York's.
Kraft-faced insulation includes a vapor retarder which helps with moisture migration from unconditioned outside air. Install kraft-faced batts with the paper facing toward the inside of the home.
One of the key benefits of insulated plasterboard is the option for foil-backed varieties, which serve as a built-in vapour barrier. However, it's important to keep in mind that ensuring the continuity of the vapour barrier at joints can be a challenge.