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Air barrier

ryoung26554 | Posted in GBA Pro Help on

I live in zone 3 central west virginia, and designed my own home,construction of which is currently under way. I have a question about the cathedral ceiling i am building which will basically be half of the house, its a monopitch design details are (from the outside in)- metal roofing, 30 lb asphalt building paper ,1/2 inch cdx, 2 by 12 rafters on 2 ft centers ,2 inch continuous soffit to ridge vent channels ( a ridgid foam pre-made), r-38 kraft faced fiberglass in the 9.5 remaining cavity, Now, for the question, my ceiling is going to be 1 by 6 t+g pine, my initial instinct is to install drywall taped mudded and painted beneath my t+g pine, however , is there a greener more natural product that i can install other than drywall for a air barrier? plywood? taped at seams with sigma or something, im building on an existing house seat that i just removed an old house from and i hate drywall, i cant help but think that areas that might be prone to slight moisture , temperature differences that drywall might not be the best material. Any and all advice or input is welcomed.

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Replies

  1. Steve Knapp CZ 3A Georgia | | #1

    RYoung,

    Drywall is usually the most cost-effective way to go. (See this article and videos for advice on installing it in an airtight manner: https://www.greenbuildingadvisor.com/green-basics/video-how-hang-airtight-drywall-1-3).

    If you can keep interior air out of your walls and attic assemblies, you reduce the risk of moisture accumulation.

    I am a little concerned about your cathedral ceiling though. Perhaps Dana will comment on the safety of the whole assembly with an R-38 batt compressed into 9.5 inches. BTW. What is your roof pitch?

  2. ryoung26554 | | #2

    ty for the quick response, roof pitch is 4-12 and the span for the cathedral ceiling is only 15 ft and according to what ive read r-30 or r-38 will fit into 9.25 cavity,,, course im up for hearing all my options. and as im learning now one source is the final word

  3. ryoung26554 | | #3

    I think the r-38 requires 10 inched but compressing .5 inches of doesnt seem to affect the r- value much, could always furr down the interior to allow more space,would also allow more room to vent , but thats a whole separate issue,,lol, getting mixed opinions about what is enough , with regards to venting a roof, some say too much can also cause problems , but i think the crux of the issue with cathedrals from what im gathering is the air barrier issue, and have enough space to vent/adequately insulate with a certain rafter width, as i will have NO penetrations on my ceiling furring or giving myself more room isnt an issue

  4. Steve Knapp CZ 3A Georgia | | #4

    We've probably read many of the same threads. It seems 1.5 to 2 inches is optimal, along with choosing a vent material that won't collapse. It's also important to have enough pitch in the roof to promote natural convection.

    I imagine you are going to avoid concealed lights and other penetrations that would compromise the assembly.

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