[Greenbuilding] some cellulose questions

[Laren Corie]

"Reuben Deumling" <9watts at gmail.com>

> My sister's attic has about 5 inches of old, possibly very old, cellulose
> dust unevenly distributed between the joists.
> (1) how much insulation value can one expect from what is already there?

Hi Reuben;

Some of the earlier cellulose had a little lower Rvalue, as well as
less effective additives.  So figure that it should exceed R3/in (R3.2),
but not reach R3.8/in.  Five inches, roughly R17+.

> (2) If I blow in more on top of this, how much is advised?

  Depends on the climate, and how much space there is,
installation cost, etc, but at least 6", and maybe another foot.

> (3) Is there any reason to fluff up what is there before adding more?

No. Though you may want to rake it aound a bit, if it is uneven.
Cellulose will have the same Rvalue (per thickness) regardless
of settlement and compression (within reason, of course)

> If so, how might one go about this?

Shovel it up, and dump it back in the hopper.  However,
there is usually some kind of foreign object, somewhere
in one of those shovel fulls.  It is generally considered to
be unwise, to blow salvaged cellulose.  It only takes one
nail to damage the blower.  I had a helper drop a screw
driver into the hopper one day.  Fortunately, it jammed
the stirring mechanism, before it got to the blower.

> (4) What is the R-value per inch assumed to be of
> dense pack cellulose and of loose fill?

Because the insulation value of cellulose comes from
the spaces within the material, rather than from the
spaces between it (like fiberglass), then cellulose
can be compressed, without loosing Rvalue (per
thickness).  So, loose fill (around 1.3 lbs/cuft)
and "dense pack" (3-3.5lbs/cuft) have the
same Rvalue, of R3.7-R3.8/in.

-LarenCorie-
Natural Solar Building Design Since 1975