[Greenbuilding] Cellulose

[JAY WALSH]

Hi Laren

I'll try to answer your questions below.
> 
>   Just curious. Do you have any evidense of that, or are you just guessing?

Having IR scanned quite a few homes (better than 30) for our weatherization
program, I have seen many walls (non dense packed) where either settling  has
occured or the cavity was poorly filled in the first place. Hard to know which
is the case years after installation. 

I've also worked on better than a dozen homes in the past three years with
blown cellulose and with several different cellulose contractors and they all
say "proper density is the key" to avoid settling.

So I'm not so much guessing as much as sure based on experience and testimony
of installers in the field that settling will occure.

As well, in attics where cellulose is blown to only 8-12 inches they must be
over blown 2-3 inches to account for natural settling (1 1/2 lbs/cu ft). In an
open bay such as you describe a similar settling will occure as you will not
be able to reach a resionable density of 3-4.5 p.c.f. 

As an example of much the density effects the settling, a dense packed wall
will use 30-40% more cellulose product than a wall that is not dense packed. 


> Perhaps your line of logic runs differently than mine, but mine tells me
that
> if holes are drilled in the drywall (or exterior sheathing) on the same
centers
> as would be used with full depth studs, that there is nothing interfering
with
> the wall being filled to its capacity and pressure. As a matter of fact,
there
> is less interference than there is in a thinner wall, where the shorter
depth
> quickly builds up resistances to the movement of the insulation, creating
> less dense spots, leading to slump. It seems that since friction against
the
> studs (or rafters in roofs) is also responsible for void spaces, 

While voids will occure with any poor installtion, I have only seen voids on
IR scans in areas where there was some odd framing, renovation framing or
blocking which could not be seen by the contractor. 

and a need
> for multiple holes, or the use of a filler tube, 

Use of a filler tube will assure a consistant fill of the cavity.

that the deeper cavities and
> lack of studs in the mid-wall would reduce the troublesome friction, there
> by reducing the need for as many holes. However, holes are no big chore,
> so using them at top and bottom, every stud space, seems the way to go.
> Cellulose slump should only happen when insulation is not packed to its
> natural settling density, which is perhaps 2lb/cuft. So, if we blow in more
> than that (~3.5/cuft), spread out thoughout the wall, it would make sense
> that slumping would simply be impossible.  

If you are able to blow a cavity as large as you describe consistantly to
3-4.5 p.c.f I would be very interested to know how it was done.

>Do you know something that
> I don't know?   Perhaps the lack of friction increases slump, but so does
> vibration, over time.  I am doing a project this summer, with even larger
> bays than Jefro's project, and I would sure appreciate any real-world
> information that you can share (links, etc) on the subject of slump in
> very thick walls, 

http://www.energycodes.gov/implement/pdfs/lib_ks_residential_insulation.pdf
http://www.eere.energy.gov/consumer/your_home/insulation_airsealing/index.cfm/mytopic=11650
http://www.cellulose.org/pdf/cellulose_bulletins/tech_bulletin2.pdf


>as well as verification that you don't really know, if
> that is the case. I would like to know if I need to create friction, or
> perhaps create a support membrane at a 4ft height. 

I have never heard of "friction" being a factor of cellulose insulation, only
as a means for friction fit fiberglass as a means to hold its self in place.
Proper density is the key to cellulose staying in place.  

Density is also the key to cellulose being a much better (but not a good as
foam) air barrier than fiberglass. 

Also, In the 80's I worked building double walled (12" - 24") superinsulated
homes in Alaska, and even a double walled dome. So I have little experience
with double wall construction as well.

>Perhaps I will
> call a couple of manufacturers, to see if there is additional com-
> -pression at full height wall depths (weight), when there are not
> a lot of close surfaces to create friction.   There do seem to be
> some factors that are beyond just thinking it through. Perhaps
> I will do a few walls in different ways, then have an IR scan
> done after a couple of years.
> 
> Thanks in advance;
> -Laren Corie-
> Climate Responsive Solar Building Design Since 1975
> www.LarenCorie.com 

I hope I have answered your questions. Good luck with the project.

Sincerely,

Jay Walsh
Center for Ecological Technology