Vapor Barrier Issue

Discussion in 'Insulation and Radiant Barriers' started by cmb1177, Aug 21, 2016.

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  1. Aug 21, 2016 #1




    New Member

    Aug 21, 2016
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    Hello everyone;

    I'm in the process of remodeling three bedrooms. The house was built in the 60s so having the walls stripped to rebuild window rough openings presented a good opportunity to improve the insulation.

    About 20 years ago, I spent a year after high school working for a contractor and when we would insulate new builds, we would use unfaced batts and a 6 mil poly vapor barrier.

    Fast forward to my home project, I figured this would be the way I'd insulate these rooms. Yesterday I was hanging drywall when I noticed the poly looked slightly, very slightly cloudy. I pulled back a staple and got a hand in there and could see there was very light condensation.

    I live in a suburb of Buffalo, NY, and it has been very warm and humid this summer. I mention that because the siding has been stripped off of the house and all the is left on the exterior is 3/4" weather sheathing and tar paper. The rooms I'm insulating are on the south and west of the house, so the sun beats on them all day. So I don't know if insulboard and vinyl siding will eventually help mitigate the heat penetrating into the walls and meeting the actual cooled air indoors.

    Obviously, I'm hoping I don't have to take everything down and redo the insulation with paper faced, but the condensation stopped me in my tracks, and I'm worried I've made a mistake; possibly miasing some detail i don't remember from 20 years ago, or even maybe just doing it wrong. I will say it's definitely a very light condensation. No one else helping me or in my house could tell unless the put their hand between the poly and insulation, and even then they needed a little convincing. That said, I'm not convinced, myself, that I've done the right thing.

    Sorry this is so long!

    Any help or advice is greatly appreciated!

  2. Aug 22, 2016 #2




    Contractor retired

    Nov 4, 2010
    Likes Received:
    Chiliwack BC Canada
    We do what you have done, we even see the edges of the poly with a black goop that you can't get. I think you have just trapped a little moisture from a high humidity day. Not sure what to do about it now.
    We have holes in the outside sheeting and house wraps let vapour thru so it would dry, but with tar paper on the outside, I am not sure.
    If you are thinking paper face would allow moisture out, then you are arguing that paper back is not a good barrier.May be just cut some slots and let it dry and tape it back up after.
  3. Aug 22, 2016 #3




    Well-Known Member

    Mar 18, 2009
    Likes Received:
    --------Welcome to the forums!-----------------

    Don't shoot the messenger...;

    No vinyl wallpaper or big mirrors (without air gap) on the exterior walls if you run an AC at all;

    You are in Zone 5; York

    Zone 5 allows paint as your vapor retarder with vinyl (vented cladding) over fiberboard;

    With your older fibrous insulation (R-11?) you will get convective loops (temperature driven) around and through- inherent with that low-density insulation. Newer R-13 (medium density) has no looping. Air seal the joints/perimeter of the fiberboard(if still exposed) to block infiltrating/exfiltrating air/moisture movement that helps drive loops in stud cavities and degrades the FG insulation up to 40%, whole wall; R-9 to R-5... links if you need them.

    Last edited: Aug 22, 2016

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