What is the R Value of a 2x6 dense packed cellulose wall?

I am reviewing the requirements of the new Maine Uniform Building and Energy Code that goes into effect 12/1/2010.  The required R value for a wood framed wall is R20. If I assume the Dense Packed Cellulose has an R value of 3.4 per inch and a 2x6 is really only 5.5" deep, then 5.5" of cellulose is only R18.7 which doesn't quite meet the standard.

I could put in R21 fiberglass and meet the standard, but I am sure the cellulose would out perform the glass in the real world.

How does everyone else view this subject?

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According to National Fiber's website a 2 x 6 wall at 5.5 " thick has an R value of R20 when dense packed at 3.5 lbs per cubic foot. The reason the Code has a minimum wall insulation requirement of R20 is because thats as good as it gets with celluloce, if the cellulose manufacturers hadn't been allowed their input the minimum would be R21 (fiberglass batts).
Thanks for the reply Scott. I found that on the National Fiber site after I posted the message.

What approach do you plan to take to get R49 in a cathedral ceiling where the slope area is greater than 500 ft2 or 20% of the total ceiling area?


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