Quote:
Originally Posted by Shin Pad
You want all insulated walls, ceilings, etc, to be air tight as possible. That means having the vapour re tarder completely sealed (including around openings and penetrations) so that you have no warm moist air from the interior of the house condensing in the insulated space during cold weather. The walls, ceilings etc., should be breathable only from the outside face of the vapour re tarder to the outside (so that any moisture that does get into this space can evaporate to the outside). This will mitigate issues with rotting studs and wood framing, mold, etc., and will make the home much more energy efficient. Bottom line - you want the house to be completely sealed. You can vent the interior through bathroom fans and hood fans when you end up with a lot of moist air inside the house - such as when taking a shower or cooking, You don't want that moist air vented outside through the insulated walls and ceilings.
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Not to be pendantic, but the air barrier is what keeps warm moist air from passing through the wall assembly and causing the majority or moisture problems. The vapor ######er just stops vapor diffusion, which is less of a problem (but still important!)
Additionally, the air barrier needs to be on the warm side of the insulation, as the dew point occurs somewhere within the insulation. For most residential construction, this means it needs to be between the gypsum and the insulation (although they really need to start building with the insulation on the exterior of the sheathing like commerical projects).