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Old 04-08-2013, 08:43 AM   #1
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insulating conundrum 2X8 Cathedral Ceilings

Good morning,
I want to introduce myself. I am brian and I am from Long Island New York, and I have a question related to insulation. Ill try to give all the particulars I can.

My house was a Levitt Style Ranch built in the 1950s, which can be compared structurally to most Cape Code Homes in the northeast. The upstairs was originally an unfinished attic, which people then converted to livable space with 2 bedrooms and a hall closet. I am re-doing only one of the rooms upstairs, so my daughter can move out of the nursery up there.

The roof was constructed of 2x6 rafters and 2x4 collar ties face nailed to every rafter. I furred down the 2x6 rafters to 2x8 nominal size. I can’t go any larger than that because of the size constraints of the room and the vaulted ceilings.

The Town Building Department only requires I put in R19 in my upstairs vaulted (cathedral) ceiling since it is a remodel…. The flat portion is a different story and not really concerned about. I know I can slap R19 up there and be to code and call it a day. But I would like to make it a little more efficient and comfortable if I can.

Due to the cost and that I am only doing one of the rooms instead of the whole upstairs I am staying away from spray foam for now.

I have the required 1 inch airspace using baffles.

Below are the 3 options I am thinking of with the last one being the one I was leaning towards.
1) Use R19 per the building department
2) Compress R30 batts (9 ) and get approximately R25 (per Owens Corning). My concern here is if I compress this into the 2x8 cavity, will I crush those Styrofoam baffles and kill my airspace? I know I don’t get the full R30 value, but it would be a little better than R19. Compression Cathedral batts are not available in my area unless I special order for a supply place (which I have had problems with selling to me since I’m not a contractor)
3) Use Un-faced R13 Batts (3 inch) and then cover these batts with Faced R15 (3 Inch). This would bring me up to a total of 7 inches of insulation. The compression would be less than the R30 crammed in and probably get close to 25-27 (in theory). I’m only compressing a little bit less than an inch for the most part. But I’m more concerned of there is an issue of the “gap” or space in between the two batts.

I know when you layer batts on top of each in a flat attic space you alternate the way you lay the batts to cut down on heat loss and air gaps. So I know you can layer the batts in a flat space but was unsure of issues in a vaulted ceiling.

Thank you for all your insight,
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Old 04-08-2013, 11:07 AM   #2
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If this is open no drywall I presume? then I would contact a contractor in your area that is certified to do a Blown in blanket system. Contact and you can find a contractor that way.
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Old 04-08-2013, 08:23 PM   #3
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How many linear or square feet do you have to insulate on the slopes?
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