# Cathedral Ceiling Insulation



## AKHermit (Oct 16, 2011)

I am building a cabin with a roof design for Valdez Alaska. 12/12 pitch with BCI 60 I joists. (2 5/16" x 14") on 16" centers. Vented at the top and bottom of all spaces. From looking on the net I've found R38 to be 10 1/2" or 12" thick. I'd like to use a kraft face to avoid any sliding issues. Will 3 1/2" vented space be to much if I use a 10 1/2" thick insulation. Not a carpenter, this place built by a safety man, truck driver and a dirt worker.


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## Windows on Wash (Aug 30, 2011)

3.5" is fine. Make sure you use a HD batt in this application.

I would also like to see some insulation webbing or housewrap between to the joist bay and the venting space to prevent the wind washing of the insulation.


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## AKHermit (Oct 16, 2011)

Are you suggesting something like this.
http://www.brentwoodindustries.com/spg/building-products/Cathedral-Ceiling.aspx


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## Windows on Wash (Aug 30, 2011)

Yes, but you can do it with Tyvek just he same.


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## Gary in WA (Mar 11, 2009)

Here in WA State, our energy code requires R-38 in cathedrals, minimum, with only -5k Heating Degree Days. You have -10k HDD for your location. I’d use 1-1/2 inch air space and foamboard, then cellulose, drywall, latex paint as on page 31, here; http://www.buildingscience.com/docu...mance-residential-buildings-all-climate-zones

Or the fiberglass with foamboard under the drywall as in the next picture, for a thermal break from the cold rafters (though they won’t transmit much as engineered-not solid wood). If the slope was shallow, then bigger airspace is recommended.

PS- check out their recommendations for your zone 7 on page 11.

I would not use any baffles that don't advertise the net free air venting rate on the spec. sheet. Example- At H.D.- http://www.bergerbuildingproducts.com/productsAccuvent.html

And O.C.- http://www.owenscorning.com/around/ventilation/pdfs/VentSure.pdf
Notice the gap between baffle ends for condensation relief....

Gary


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## Windows on Wash (Aug 30, 2011)

I like Gary's roof approach better.

Rigid foam against the inside edge of the outer flange, insul web the joist bays, blow cellulose, and then a layer of rigid foam against the inside surface.

You would have a vented near R-50 insulation layer at that point.


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## AKHermit (Oct 16, 2011)

I think I should add that this is a recreational cabin off the road system. Access by snow machine, atv or walking.


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