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The R-38C they offer seems to be intended specifically for 2x12 rafters. It would definitely be better than the R-30 you said they have on site, maybe that is intended for elsewhere. The only aspect I don't care for would be omitting the baffles or chutes and I like them larger than 1" and so do the experts. Citations available. Their 10 1/4" batt is 1" less than the 11 1/4" depth you have and requires the ventilation to flow directly above the fiberglass insulation. In reality the colder air will filter down through the insulation reducing its performance, thus some sort of chute is desired along with protection at the bottom to keep incoming air off of the end of the insulation. Here is one specifically listed for cathedral use:
http://www.bestmaterials.com/detail.aspx?ID=19459&gclid=EAIaIQobChMIj_ODuoCD2QIVFLjACh3h1QWiEAQYASABEgK3YvD_BwE

Should be available at other locations.

Bud
 
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Discussion Starter #23
Well, I spoke with said builder, and learned his plan ( as advised by Insulating company)
they are suggesting to use R30 for ceiling as the R38 wont fit in rafters with baffle.
I inquired about the R38C which is intended for cathedral with 2 x 12 and he still thinks there will be a vent spacing issue, but is going to check with the insulation company, he did say foam will cost more ... but that doesn't tell me much of anything ,
This is leaving the brunt of this on me, I will NEED to figure this out myself it seems and request they do what I want as opposed to what they *think*, I told him I'm not interested in getting "by" any code ..I live here and want it done the BEST way possible, I am convince of a couple things here,
1) builder is inexperienced AND has issues in personal life so not as dialed in as needed.
2) Insulation company are idiots... if they suggested the R30 ..when code is R38
So I' m now re reading and scouring the internet trying to find the solution to present to them to be sure our insulation is done well.
It sure does suck having ZERO faith in someone in charge of your dream.
so that's all for now
any insulating company want to give me the recipe???
 

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First, it shouldn't be just you. Being a new addition there should be a permit that was pulled and typically associated with permits are inspections. Assuming yes, then locate that inspector or department and ask them what they need to see to pass inspection.

Second, you have a set of plans calling for r-38 and I assume that was what the contractor bid on and agreed to and I assume the insulation contractor looked at the same plans. Both of them are in this business as professionals and should have been planning on r-38.

The Owens Corning insulation you linked: http://www2.owenscorning.com/literature/pdfs/21151-D EcoTouch R-38C (for 2x12 Cathedral Ceilings) Data Sheet.pdf

Looks like exactly what you need. It is a high density product designed to provide more r-value in less space. 10¼", R-38C EcoTouch ®Insulation Batts. It should have baffles all the way to the upper vent area to be sure it does not infringe on the vent space or suffer from "wind washing" at the lower end as air comes in. All standard practices they just need to get onboard.

Print out or send them the link to that product. A quick search indicated it is available from Home Depot, confirm that for your area.

Bud
 

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Discussion Starter #25
Yes Bud, a permit has been pulled, I've yet to see the inspector, I'm calling tomorrow to ask what the inspection schedule is, not sure if you know from previous posts but I also have a foundation issue with this build, (it has a leak on both corners where it joins our existing house) I don't even think the inspector came out to see the foundation. Maybe the builder hasn't called him...(wouldn't surprise me at this point),, allow me to clarify something.. I refer to him as "the builder" when in actuality hes ore the gc... we .have a very skilled carpenter here who has been doing everything... (mostly alone) the the "builder" is seldom here, the thing is this "builder" contractor is the one hiring subs for this ...and I'm shocked an insulation company would suggest R30... oh the R30 here is for the cantilever, I learned the plan was to put that along with plywood sheathing ,Tyvek , & vinyl to insulate the cantilever... something else to request differently I imagine.. does it matter which vents they use ?? I heard properVent mentioned, but looked at the liknk for the one you mentioned, I printed the spec sheet to show him, is there a "better" one ???
Thank you for your help, I appreciate it.
 

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There are several varieties of vents but I personally like to create my own with 1" rigid insulation held off of the roof by 1.5" or 2" strips if rigid. It depends sometimes how the depth works out with the insulation I want. Been awhile but if I were building today I would be using Roxul. For your 2x12's (11.25") I would probably use 5.5" plus 3.5" plus 1" rigid. That would be r-23 plus r-15 plus r-5. I would rip 1" rigid to give me 1.25" strips for the edges to space the air gap. Insulation and then a vapor barrier depending upon what is required/desired.

The important parts of a cantilever are insulation and air sealing, both are emphasized in this link. https://basc.pnnl.gov/resource-guides/cantilevered-floor
I like a solid covering on the bottom like plywood and no ventilation.

Before I forget, are your 2x12's regular wood or engineered "I-Joists"? I-Joists would change your approach to insulating a lot.

Bud
 

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Discussion Starter #28
So it sounds almost like the cantilever plan is ok ?? I briefly looked at the link and it sounds similar to their plan, they already have blocking from the basement room side, so all work will be done from outside.
 
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