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Batt insulation

Bill Stretzinger | Posted in General Questions on

I’m in the process of buying a home (Metro New Orleans, Zone 2A, very warm and moist) for my daughter and noticed the attic insulation was installed with the Kraft paper facing up. That problem is being corrected by the seller, but now I wonder if the wall insulation was installed incorrectly as well. When given an opportunity to re-inspect this coming Monday I will be removing electrical covers and other things to see if the insulation problem continues with the outside or exterior walls.

I searched in vain on the internet for the correct answer, but it looks like some experts disagree about the Kraft paper facing in or out. Does it matter? Can someone help?

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Replies

  1. Expert Member
    Dana Dorsett | | #1

    In cooling dominated US climate zone 2A, the vapor retarders SHOULD be on the exterior side of the assembly.

    But with kraft facers it doesn't matter a whole lot. A kraft facer is a "smart" vapor retarder- if it ever gets damp enough to support mold growth it becomes fairly vapor open (5+ perms), and the moisture can leave. When bone-dry they run about 0.5 perms, which is fairly vapor retardent.

    Still, in New Orleans the summertime outdoor dewpoints are often in the mid to high 70s F. When the rooms are air conditioned to a temperature below the outdoor dew point it's good to have a vapor retarder on the exterior side of the fluff, which in the attic would be the top side. That limits the amount of condensation/adsorption you get in the ceiling materials by slowing the rate at which moisture will diffuse into the fiberglass layer.

    The wintertime moisture drives from the interior are very small by comparison- the attic temp is typically well above the indoor dew point in that climate.

    But in zone 4 & colder it's worth paying attention to putting the facer on the conditioned space side of the assembly though, since the wintertime outdoor temps dwell below typical indoor air dew points for weeks or months on end.

  2. GBA Editor
    Martin Holladay | | #2

    Bill,
    To summarize what Dana said: The builder of your home was one of the rare contractors in New Orleans who actually got this detail right.

    That said, don't worry about it. In your climate, the kraft facing can face either direction without problems.

  3. Expert Member
    Dana Dorsett | | #3

    Now why couldn't I have said it that succinctly? :-)

    Thanks Martin!

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