Vapor Transmission Through Ceiling To Attic

So it certainly makes sense that that vapor would rapidly diffuse through the foam and make the attic even more humid once the sun hits the roof deck.

Vapor transmission through ceiling to attic.

Thanks for some very informative posts by all. If it is and you plan to provide heating and cooling to the finished attic space you need to remove. Standard batts and high performance batts can be used under floors. Multiply by the appropriate factor from table 1 below to learn the total gross vent area needed.

For instance the building code s ratio of one square foot of open ventilation area to 300 square feet of attic square footage assumes a vapor barrier is installed between the ceiling and the attic space to retard the migration of moisture vapor into the attic. So compared to that hot humid attic the vapor pressure at the other side of the foam is a factor of six higher. Determine where vents will be located. In the old days in severely cold climates where attics were poorly insulated it was okay to omit a plastic ceiling vapor barrier.

The heat loss from the house warmed the attic sufficiently to allow attic ventilation to remove moisture from the attic. Lastly i am curious about the recommendation on your blog to reverse the ceiling fans to decrease the radiant heat transmitted from the attic through the ceiling. The science of moisture movement. Insulation and exit the attic through the roof vents.

Water vapor can pass through building materials in several ways including direct transmission and by heat transfer but studies suggest that fully 98 percent of the moisture transfer through walls occurs through air gaps including cracks around electrical fixtures and outlets and gaps along baseboards. Floor insulation can also help with sound transmission so it can make sense to use it even between two conditioned spaces. When insulating floors over unheated basements or crawl spaces faced products should be used and vapor retarders should face heated areas and be in. Thus installing vapor barriers on wall surfaces must.

Divide this number by either 150 no vapor retarder or by 300 vapor retarder in place. That is a new one on me. The vapor barrier is always installed facing the heated side of the wall or ceiling because that s where the moisture is coming from.