[Greenbuilding] [BULK] Re: (no subject)Cellulose

[Lawrence Lile]

Cellulose is specifically NOT recommended to be used with plastic vapor barriers.  First, it is often wet sprayed, and it needs to dry.  Second, even if it is blown dry, they still don't recommned vapor barriers, because cellulose can absorb moisture.  If it isn't allowed to dry, you can cause trouble. Surround it with materials that allow moisture transmission but retard air leakage. 
 
Cellulose is an unusual insulation material.  I understand that is does not insulate by trapping air, as most other insulations do, so the dense packed cellulose has a higher R value than loose packed.  Dense packed cellulose is better at retarding infiltration than loose packed cellulose, or fiberglass.  http://coloradoenergy.org/procorner/stuff/r-values.htm
 
Cellulose also has the wonderful property of slightly increasing R value at low temperatures.  Fiberglass, on the other hand, loses R value dramatically when it gets colder outside An R-19 wall can be as low as R9 at very cold temperatures.  This is a characteristic that the Fiberglass industry does not want you to know.  http://www.foam-tech.com/theory/rvaluedrift.htm
 
Infiltration is the cause of most moisture problems in walls, not vapor transmission.  (We say this over and over here, but the Public doesn't believe us)  Warm, moist air creeping into your walls through openings such as electrical outlets causes the bulk of condensation, and plastic vapor barriers don't do anything to stop that.  
 
My approach is to caulk inside stud cavities before the insulation goes in.  Caulk horizontal gaps in sheathing, top and bottom plates, framing around windows, double studs, and anywhere daylight shows through the wall sheathing.  Then wrap it with foam and tyvek.  Then caulk around electrical outlets and add foam gaskets under the covers.  Skip the plastic, it's best use is as a tarp over your lawnmower.  
 
--Lawrence Lile

George wrote:

>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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