Flash & Batt Systems - and questions on mutiple vapor barriers in a wall?
Last Post 16 Oct 2012 10:58 AM by Dana1. 1 Replies.
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DJVUser is Offline
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07 Oct 2012 02:24 PM
I'm still going over insulation quotes and my last quote contains a flash and batt option ( 1" CC foam in walls and marginally compressed R13 Kraft faced batts )

My question is : are the multiple vapor retarders in the same wall a problem? it seems to me it would be like putting kraft facing on both sides of the wall.

The 1" on the walls is somewhere around R7 based onthe information I have been reviewing and is that enough to stop moisture?

Does anyone see a problem with this?

also a similar setup can be used in the attic - 2.5" CC SF folowed up with a batt insulation - another contractor wants to just apply the 2.5" foam

Any feedback would be appreciated

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16 Oct 2012 10:58 AM
At 1" most closed cell foam is a bit over 1-perm, and even the tightest are in the ~0.7-0.8 perm range, which is NOT a problem from a drying capacity point of view. And even when the inner surface is below the dew point of the cavity air it's protective of the sheathing, since foam won't wick the micro-droplets up the way wood fiber does. Kraft facers run around 0.4 perms, so the air in the cavity will track the exterior dew point averages more closely than the interior dew points, yet it'll have decent drying capacity in both directions.

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