In cold climates, the vapour retarder is installed on the warm side – typically directly behind the drywall. This location prevents the warm and relatively humid air from traveling into the wall where it may condense. But here’s the thing: Building scientists agree that the use of vapour impermeable retarders or barriers are not always necessary and in fact can be a poor strategy in all except the coldest climates such as northern Canada and Alaska. This is because the use of vapour impermeable barriers has two significant flaws:
