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Old 10-19-2018, 03:41 PM   #76
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Re: Cathedral Ceiling Redo


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Originally Posted by Nealtw View Post
You don't want any moist air from the house getting in there. If it were here it would get a 6 mill poly before the drywall,

I know Bud's idea was to 1) use rigid foam to prevent room moisture from hitting the cold roof deck 2) have the air channel vent any moisture that did get through

Not sure about where the blocked moisture would naturally go. But I could see 6mm plastic trapping moisture behind the sheetrock, no?
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Old 10-19-2018, 04:20 PM   #77
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Re: Cathedral Ceiling Redo


If the channel doesn't have a lower inlet to work with the high vents then the ventilation basically isn't going to work.

I'm out of ideas.

Bud
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Old 10-19-2018, 04:27 PM   #78
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Re: Cathedral Ceiling Redo


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Originally Posted by arcticranger View Post
I know Bud's idea was to 1) use rigid foam to prevent room moisture from hitting the cold roof deck 2) have the air channel vent any moisture that did get through

Not sure about where the blocked moisture would naturally go. But I could see 6mm plastic trapping moisture behind the sheetrock, no?
There should be no moisture in there so it is a matter of keeping it out and there is a different theory for different areas and climates. mostly what you worry about is a leak that would allow house air to get to the vented air above. If that happens warm air would cool on the way and any moisture would condense somewhere, usually beside the rafters where the thermal bridge is and air might find a path. that's not to say air travels thru drywall but it is the holes mostly like wires thru the tops of the walls and light and fan fixtures.
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Old 10-19-2018, 05:14 PM   #79
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Re: Cathedral Ceiling Redo


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Originally Posted by Bud9051 View Post
If the channel doesn't have a lower inlet to work with the high vents then the ventilation basically isn't going to work.
Quote:
Originally Posted by Bud9051 View Post

I'm out of ideas.

Bud



Yea the assembly will stay as it is with sheetrock for air seal, no plastic or Tyvek. I can do some cool decorative things like faux-beams on the sheetrock.



Anyway you can't quit you're my architect
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Old 10-19-2018, 07:08 PM   #80
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Re: Cathedral Ceiling Redo


LOL, I didn't say I quit, I said I was out of ideas, or at least conventional ideas.

If you leave a gap but have no lower intake there will still be a small amount of natural circulation, cold air wandering down into those dead end cavities and displacing the slightly warmer air and push to join the air above and reach those higher vents. In addition, any moisture that passes to the ait results in lighter air, just like we think about warm air being lighter. So between a small amount of heat and a small amount of moisture the air will circulate a bit.

A tip for all who bury their attics in lots of insulation, plan on a way to get back uo there without destroying the new insulation. In one large attic I created a raised walk down the center and it sure was handy. In many attics I have been in the kind framers left some 2x6's flat across the tops of the joists. Not perfect but better than trying to find each joist to step on.

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cathedral ceiling , hot roof , polyiso insulation


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