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Cathedral Ceiling Insulation Options

Post in 'The Green Room' started by Bret Hart, Jan 3, 2013.

  1. Circus

    Circus Member

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    I just skimmed over the responsives and maybe someone commented already. I didn't see any ice dams in your pictures. At least anything caused by escaping heat.
    When the air temperature is near freezing and you have two feet of snow insulating the roof there's going to be a little melting no matter how well insulated. The question is how often. Once every five years or once a day. Rot needs a lot of soakings.
    Vapor barrior faults cause water stains on your ceiling.
    ScotO likes this.

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  2. Bret Chase

    Bret Chase Minister of Fire

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    I don't use kraft paper faced insulation..... ever... There can only be a single vapor barrier in the whole system... otherwise you run into moisture problems...
  3. Bret Chase

    Bret Chase Minister of Fire

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    Ugh... modular housing... my brother has a modular, brand new in 2005... my house was built in 1865... he spent more than I did to heat his house with LPG than I did with K1.... K1 far more expensive than LPG (especially since he is getting the Selkirk rate....) and my house had NO insulation!. figure that one out...

    BH, building a house as you've described is excellent from a fire prevention point of view... not always great from a energy savings point of view... pay close attention to where the modules were joined.... that is where you will lose the most heat.
  4. 91LMS

    91LMS Member

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    with only having insulation and whichever material is chosen to finish, whether it be sheetrock, t&g, etc., are you saying paper faces is still a bad choice then?
  5. Circus

    Circus Member

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    You can lay a plastic barrior on the kraft paper side (interior) of kraft paper insulation. That still would only be one vapor barrior. Without all the holes.
  6. Bret Hart

    Bret Hart Burning Hunk

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    No stains on the ceilings and thanks for pointing out the normal melting issues.




    Thanks BC. I spent some time with the IR temp gun and noticed that there was a bit of difference at the center of the house where they are joined. Going to pull the molding down and seal things up some when I get through the overload of work in the shop. Just been trying not to look at the ice since this is my busiest time of year.
  7. Bret Chase

    Bret Chase Minister of Fire

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    Using unfaced batts and covering the walls with sheets of 6 mil poly with TAPED seams is far, far better as a vapor barrier than kraft paper is. paper is far too easily damaged and detriorates fairly quickly within the wall space..
  8. Bret Chase

    Bret Chase Minister of Fire

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    in that case, you'd be better served pulling the faces off the batt.... otherwise you're going to end up with water trapped between the poly and the paper...
  9. woodgeek

    woodgeek Minister of Fire

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    Just to be precise.....kraft paper is a lousy air barrier and vapor barrier (air and vapor both go around the paper). Properly detailed poly is a great air barrier and vapor barrier....but in most lower 48 climate zones a vapor barrier is not required (or can be bad) if a proper air barrier is in place. Intact drywall, with sealing of penetrations and framing gaps can be an effective air barrier while maintaining a small amount of (beneficial) drying capacity.

    Torn/perforated kraft paper FG behind drywall is harmless, so long as there is no conditioned (humid) air moving in the cavity.

    Poly is ok/recommended in Canada and (more or less) the US states on the canadian border.
  10. Bret Chase

    Bret Chase Minister of Fire

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    a vapor barrier is most definitely required by code and is the standard practice in the state of Maine.... whether it was done properly or not... is an entirely different story...
  11. woodgeek

    woodgeek Minister of Fire

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    And one of these days....it will be dropped from the code.
  12. Bret Chase

    Bret Chase Minister of Fire

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    I don't see that happening... with the MUBEC... the push is towards buildings so tight that w/o makeup air... the occupants would die in a day or two...
  13. woodgeek

    woodgeek Minister of Fire

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    And when they are airsealed (at the drywall, housewrap, etc), there is no need whatsoever for poly.
  14. Circus

    Circus Member

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    Wrong. Without a vapor barrior water condenses on the cold inner surface of the exterior wall and the cold exterior surface of the insulation. Shortly the insulation becomes soaked, the rafters drip water onto the ceiling and your building rots.
  15. Ehouse

    Ehouse Minister of Fire

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    I've used a vapor barrier primer in bathrooms instead of poly.
  16. semipro

    semipro Minister of Fire

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    This is actually fairly controversial. Conventional knowledge may be outdated.
    These are really good articles on the subject which I strongly recommend those here read
    http://www.greenbuildingadvisor.com/blogs/dept/musings/do-i-need-vapor-retarder.
    http://www.greenbuildingadvisor.com/blogs/dept/musings/vapor-retarders-and-vapor-barriers
  17. begreen

    begreen Mooderator Staff Member

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    FWIW, our house is 88 yrs old. It has no vapor barrier and no house wrap. It was insulated about 16 yrs ago by a previous owner. When we did the remodel in 2006 a few walls were opened to make way for window or partition changes. Rodent damage we found in one area, but rot or moisture, no.
  18. woodgeek

    woodgeek Minister of Fire

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    Controversial is a good way to describe it. Semi's links are good, I also like:

    http://www.energyvanguard.com/blog-...54110/You-Don-t-Need-a-Vapor-Barrier-Probably

    Moisture problems are due to the leakage of conditioned air, not diffusion through sheet goods. A wall that has air leakage through the cavity and a vapor barrier between the interior and the cavity is still wet (due to the air leak) and can't dry (b/c of the poly).

    Scotty did the right thing putting poly in his ceiling b/c he was using T&G boards, he needed something as an air barrier (tyvek would have been good) but poly was ok since the roof was vented above the insulation....it could dry upwards.
  19. Bret Chase

    Bret Chase Minister of Fire

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    that's because your house most likely leaks air like a sieve... just like my almost 150 year old house does... all that air leakage carries the water away with it...
  20. begreen

    begreen Mooderator Staff Member

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    Exactly, there are no absolutes.
  21. RustyShackleford

    RustyShackleford Minister of Fire

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    I'd guess the same. If it's a cathedral ceiling, you're not gonna get that much better than R30, maybe R38 (and you'd have to add bafflles). A little arithmetic will show you that's not worth much.

    Your btus/hour per degree-fahreinheit for your 2000 sqft ceiling will go from 2000/30 to 2000/38, reducing that number by about 14. So over the course of a 5000 degree-day winter (typical for your area ?), you will save about 1.7 million btus or 500 kilowatt hours. Using electric resistance heat and a typical 10 cents per kwh rate, you'd save $50 a year (in heating). Use a heat pump or natural gas (or A/C, which is also a heat pump) and it's way less savings.

    Of course there's also the issue of comfort (as was pointed out to me when I posted a similar calculation while wondering aloud whether to go with more expensive window glass), but as others have pointed out, air leakage has a vastly more important effect on comfort.
  22. welderboyjk

    welderboyjk Member

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    I've got a question for the original poster, with all of the snow that I can see in the two roof pics you posted I'm guessing that your vents near the peak of the roof were covered, correct?
    Absolutely NO insulation is perfect, the purpose of venting is to let the heat that does wander through the insulation out. If they were covered I can see why you had some ice. BTW it didn't look that bad to me either.
  23. Bret Hart

    Bret Hart Burning Hunk

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    Just noticed that I missed this post. The vents were definitely covered after that snow in the pics but much of the 3 inch thick ice at the edge of the roof was there prior to that deep snow. The vents had been clear and working.

    Thanks for all the help and for the reassurance that maybe it's not too bad after all.

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