Cathedral ceilings and insulation

Charles McCorkle
12/17/2010
Hello, I've been reading for a while and enjoy the forum. We are building a cabin here in Mississippi and are almost to the roofing point. We have very high cathedral ceilings (12x12 pitch) with exposed rafters and 1x12 pine decking, also exposed. My contractor has applied 30lb felt to the outside of the decking, 2x4 lathe laid flat and has recommended Dow Blueboard as insulation between the lathing, more felt then the metal roofing panels. My concern is not having enough insulation. What are some ideas for this scenario to give us the proper R values and also ventilate in this narrow space?
Eric Novotny
An informed customer is the Best Customer!
12/17/2010
You are also going to loose a ton of heated air through the decking boards. If you could go back, I would have highly recommended that you used a peel and stick ice/water membrane of the entire decking board section to air seal it. Dow board does not have a very high R-Value per inch. I would look to a polyisocyanurate board instead. If you were a very dominant heating climate with heavy snows, there would be other considerations but that is not the case here. A good thermal isolation/break barrier will do the job just fine as it will keep the roof heat from transmitting into the home. This site has some good articles about foam roof decking. http://danperkinsroof.com/articles.htm
Guest User
12/17/2010
Thanks for the quick reply! The roofing manufacturer suggested a product called double bubble or bubble wrap. It is about a 1/4" thick and has an R value of about 10. I thought about doubling this with the hopes that it would double the R value and still allow for ventilation. Your thoughts?
Eric Novotny
An informed customer is the Best Customer!
12/17/2010
Your roofer does not understand insulation in this case. That bubble wrap is a radiant barrier and does not have application value in the roof that you describe. Polyisocyanurate foam has the highest R-value on the market and it is only and R-8 at the most per inch (R-2 per 1/4 inch). Radiant barriers have application value in some cases but not unless you have adequate insulation to begin with. You don't need ventilation in that roof style and especially if you seal up the roof decking boards.
redsaf dase
consortium of metal roofing
12/21/2010
Polyisocyanurate foam has the highest R-value on the market and it is only and R-8 at the most per inch (R-2 per 1/4 inch). www.plrprivatelabelrights.com
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