[Greenbuilding] (no subject)Cellulose

[George J. Nesbitt]

You are right most insulations works by trapping air. Packing cellulose 
denser will reduce its R-values some, but you also gain greater 
resistance to air flow. Standard Cellulose is blown in at 2.6lbs per 
cubic foot, but Dense Pack Cellulose should be 3.5 to 4lbs per cubic 
foot, this only adds 0.4lbs per square foot of 2"x4", and 0.64lbs per 
square foot of 2"x6", so it doesn't add much mass.

Susan Buchan wrote:

>I was talking with a local tradesman recently who had attended a talk by another tradesman who specializes in insulation problems. During the talk the insulation guy mentioned that he recommends packing wall cavities that will be insulated with cellulose as tightly as possible behind a poly barrier. He emphasized you can not pack it too tightly, leaving tiny/no air voids, and apparently showed some infrared scans as proof that this works better than more loosely packed cellulose. 
>
>I am aware of the importance of completely filling all voids, but this information seemed to be in direct conflict with the notion that trapped air is an excellent insulator, and the premise that tightly packing insulation reduces R values.
>
>After thinking this over, and taking into account that cellulose is cheap and recycled, I wondered if this effect was the same as rammed earth construction, that is, the tighter the soil pack, the greater amount material that absorbs and retains heat, and the longer thermal lag. Any thoughts from the technically inclined? 
>
>Susan Buchan
>Sage Design
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