[Greenbuilding] was Diminishing returns / obsessingover bridging

[Laren Corie]

"Lawrence Lile" <LLile at projsolco.com>

> DIY blown-in cellulose, installed between existing studs
> and not done by a pro will probably settle and have gaps.  
> 
> --Lawrence Lile

     I have seen no factual basis for such a statement.  There have
definitely been bad blown-in wall installations, by unscrupulous pros
who have cheated homeowners by using too little material. However,
there is nothing to suggest that a DIYer would ever short himself,
when the only way to tell that the wall cavity is full is that the blower
stops moving insulation and the hose buckles.  You simply fill the
hole until it won't take any more insulation. Cellulose will naturally
settle to roughly 1-1/2 lbs/cu ft density.     It gets blown into walls
at between 3.25 and 3.75 lbs/cu ft. So, it is packed in way tighter
than its natural settling density (like a spring, or foam rubber in a
cushion). Vibration will not cause it to settle. It does the opposite.
It will cause it to expand into every tiny area. Since there is far more
cellulose in the wall cavity, than its natural settling density, it simply
can not slump. It would be highly unusual for any area of a wall
cavity to remain empty when that same cavity was filled with
insulation.  Locating the holes is not a complicated task.  A
hole near the top, and another near the bottom, will give even
enough packing for no slumping to occur in normal height walls.
Taller walls simply get an additional hole. Since the insulation value
of cellulose is in the fibers, instead of in the gaps between, there
is no loss of R value by increasing the density over that used
for loose fill installations. At either its loose fill density, or the
'dense-pack' density, the R value is around 3.7-3.8/in.

However, there has been evidence that some foam insulations
can lose their bond with studs, leaving gaps where air can
pass.  This is why gaskets are beginning to be used around
windows and doors, instead of foam fills. This loss of contact
should not happen with 'dense-packed' cellulose, even in 
narrow spaces, where there might be frame movement.

-Laren Corie-
Natural Solar Building Design Since 1975
www.LarenCorie.com

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