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Non Vented Cathedral Ceiling

 
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Old 05-21-2012, 07:03 PM   #1
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Non Vented Cathedral Ceiling


We have a cathedral ceiling that is being insulted with r-38 kraft faced fiberglass. My insulation contractor wants to put air baffles/channels in first even though there is no intake or exhaust vents. The i joist construction specified blocking at every bearing point that cut off ventilation. The roof is standing seem metal. I don't see what the air baffles will do in this situation but the insulation contractor says it will condensate on the underside of the roof deck if we don't have them. Anyone out there able to explain the science in that theory?
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Old 05-28-2012, 02:44 AM   #2
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Re: Non Vented Cathedral Ceiling


Are you using an actual approved system?

I personally would vent the roof properly or use spray foam.

Dense packing cellulose would probably also work.

Don't just guess or assume, use a proper approved system.

The baffles are part of a vented system. Without venting they won't make a difference. Either way here you are going to have condensation problems in your roof unless you follow a proper system.
Do Not close this in before you consult an expert and make sure your roof system is going to work. Condensation in a sealed roof system means water with nowhere to go.....


You definitely need an expert involved.

Steve

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Old 05-28-2012, 07:51 AM   #3
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Re: Non Vented Cathedral Ceiling


I think all I-joist manufacturers allow cutting a V-notch in the top of the blocking to allow for ventilation. It might require changing out the type of blocking you used, but there are a couple of ways to do it.

I agree that you should do some more research into building a system that will not trap moisture.
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Old 05-28-2012, 08:05 AM   #4
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Re: Non Vented Cathedral Ceiling


Does the metal roof have any venting?
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Old 05-28-2012, 08:32 AM   #5
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Re: Non Vented Cathedral Ceiling


Even with the baffles at the low end of the roof, make certain to have venting at the top as well.

It is not uncommon around here to also add cross-rafter strapping below to roof sheathing to allow for any restricted air to move sideways into a neighbouring bay to be vented properly.

It might be worthwhile to have an on-site inspection made by "some one who knows stuff".
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Old 05-28-2012, 12:28 PM   #6
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Re: Non Vented Cathedral Ceiling


We had an insulation inspector at the property with the insulation contractor. The final product ended up being 2 inches of spray foam and then fiberglass. It's what both decided would be the best. There is no intake or exhaust air. The insulation contractor wrote a letter stating what they did and guaranteeing its the only way they wanted to do it and stating that we would not have any moisture problems due to their insulation installation methods.
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Old 05-28-2012, 12:29 PM   #7
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Re: Non Vented Cathedral Ceiling


Quote:
Originally Posted by TNTSERVICES
Does the metal roof have any venting?
The metal roof does not have any venting. It's a standing seem style.
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Old 05-28-2012, 05:49 PM   #8
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Re: Non Vented Cathedral Ceiling


That is how most non vented assemblies are done around here now, otherwise called "Flash and Batt".
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Old 05-28-2012, 05:54 PM   #9
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Re: Non Vented Cathedral Ceiling


Do you know if the foam was open or closed cell? 2" is about the minimum i would go with a flash and batt. Sounds good. Better than what you were talking about earlier
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Old 05-28-2012, 06:05 PM   #10
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Re: Non Vented Cathedral Ceiling


Closed cell
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Old 05-28-2012, 06:49 PM   #11
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Re: Non Vented Cathedral Ceiling


Closed is good. I prefer dense pack cellulose over batts any day, but the foam is rally what the envelope needed to pull off the hot roof.
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Old 06-08-2012, 09:44 PM   #12
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Re: Non Vented Cathedral Ceiling


Flash and batt is what its called, yes. 1 1/4" off closed-cell is manditory fore flash. Why you might ask 1 1/4". Closed-cell foam needs what it is called a cream time, ( Two chemicals to mix and react to temperture to create its form ), anything less would be subject to stress and cracks related to improper cureing of the material. In a roof deck system 3" of closed-cell is what you need. And its only an R-21. Thats all you need with foam.....

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