I’ve been doing some research on insulating a home.
By no means have I grasped the whole concept, but from what I have been reading it seems I am more confused than ever.
Apparently up north where the cold dry air is more the norm your insulation vapor barrier on the walls should face the interior heated side of the house.
Where I live mostly hot and humind conditions it appears that the vapor barrier should be on the OUTSIDE of the house (tyvek doesn’t count).
If this is true, why does EVERY house I see being constructed have the kraft paper batts facing the inside of the house???
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WWPD
Replies
>>"If this is true, why does EVERY house I see being constructed have the kraft paper batts facing the inside of the house???"
In Tampa, maybe 'cause they're built wrong. When warm, moist air hits cool, you will usually get condensation. The condensation occurs at the point where the warm, moist air cools to its dew point. That point is usually somewhere inside the insulation itself so if the VB is on the wrong side, insulation that is porous to air and water vapor gets wet (fiberglass, for example).
Object is to keep the warm, moist air away from the cool. In the north, the situation occurs in the winter so VB is inside. In paradise (I mean in places where it's warm even in winter), you want to keep the outside warm moist air away from your air conditioned interior.
Use sprayed in foam and it's no longer an issue. Dewpoint "zone" is still somewhere in the insulation, but the insulation won't pass the air and water vapor, so no condensate in the wall.
"A job well done is its own reward. Now would you prefer to make the final payment by cash, check or Master Card?"
Edited 3/7/2006 9:24 am ET by philarenewal
http://buildingscience.com/housesthatwork/hygro-thermal.htm
http://buildingscience.com/topten/south.htm
The kraft paper proobably works in most cases because it is not that good of a vapor retorter, specially when it is not carefully installed.
Put poly on the inside of a wood frame building like they do up north and the wood frame house would be mush in a couple of years.
I'm glad that Bill H. has already suggested visiting the http://www.buildingscience.com website - they have some excellent articles on designing for moisture control. Nowadays the design philosophy is not to incorporate absolute vapor barriers into wall assemblies but to build wall assemblies that allow vapor to permeate in a controlled manner and thus dry and/or control internal wall temperatures such that water vapor will not condense within the wall cavity. But, different climates require different designs, or one design doesn't fit all cases.
Yeah, I read about a product called
MemBrain
that sounded promising-----------------------------------------------------------------------------
WWPD
How about encapsulated insulation, it would be informative to look into its use in the wall cavity.