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Old 01-19-2010, 07:59 PM   #1
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Insulating Vaulted Ceiling


Current rafters are 2x6 24 o.c. For about 4' the ceiling will be vaulted until it flattens out. I live in Iowa and ceiling insulation says I need R-49. That would be impossible even with adding furring strips.

is there a difference in what code says is acceptable for vaulted ceilings? Or since the there will only be a few feet, is a 2x6 acceptable for insulation?

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Old 01-19-2010, 08:10 PM   #2
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foam or foam board might be the answer. be sure to vent above it.

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Old 01-19-2010, 08:12 PM   #3
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Even with foam board (R-5 per inch) I can only can R-25. I just need to know if there is something in code that says a vaulted ceiling can be less than a standard ceiling.
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Old 01-19-2010, 08:14 PM   #4
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High R-value foam for the vaulted area?


Ask the inspector for his/her ideas. Ultimately it will be their decision to approve or reject.

You may be able to over-insulate the flat portion of the ceiling, higher than the specified R-49, so that the overall average insulation value of the entire ceiling area meets the R-49 requirement.

R-49! Dang, that is a lot of insulation.
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Old 01-19-2010, 08:18 PM   #5
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Quote:
Originally Posted by cibula11 View Post
Even with foam board (R-5 per inch) I can only can R-25. I just need to know if there is something in code that says a vaulted ceiling can be less than a standard ceiling.
Nope, required insulation to meet code is what is required
In some cases they may average it, but I had to meet specific insulation for walls & ceiling
Some people go to spray insulation for better results
I have R38 & may add some rigid foam board for more insulation
I use 2x12's, 2x6 just can't hold enough insulation
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Old 01-19-2010, 08:18 PM   #6
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Don't mention the 1-2" air channel above it, may be required.

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Old 01-19-2010, 08:22 PM   #7
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I planned on creating the airspace. I guess since the 4 ft space that will be vaulted is so small, I could sister with 2x12's and add insulation that way. I'll have to check with me inspector.
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Old 01-19-2010, 09:02 PM   #8
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Can super tuff r be used back to back or would it create a bunch of moisture issues? If so the dow site claims it is 6.5 R per inch plus an additional 2.8 for a 1 inch air space. Also on their site http://building.dow.com/na/en/tools/...athvaulted.htm they talk about it being installed over the rafters followed by drywall. That would gain him another 6.5. Plus if he adds a furring strip he could put in another layer of board.

Wouldn't be cheap, but I think he already mentioned foam boards.
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Old 01-29-2010, 09:35 PM   #9
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I had my inspector come out and he mentioned I would need R 43. I thought that was an odd number and I wonder if he misunderstood where I needed the insulation. I know we use the 2003 IRC. Anyone have info on what that particular code says about R value on a vaulted ceiling.
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Old 01-29-2010, 10:12 PM   #10
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Have you checked online to see if your county has a website. I've seen some counties with some pretty decent website. Maybe yours has a list of the codes for your area.
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Old 01-30-2010, 04:44 PM   #11
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http://www.ornl.gov/sci/roofs+walls/...on/ins_16.html

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Old 01-31-2010, 08:48 AM   #12
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closed cell spray foam can achieve upward of R7-R8.5/inch actually.

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