[Greenbuilding] [BULK] Re: Cellulose settling/blowing

Thu Jul 27 16:03:43 CDT 2006

George, 

Wow, you've been around a bag of cellulose a few times! 

Here is an installation problem:  I have a cathedral ceiling, 24" deep
roof truses, and ventilation planned for above the insulation layer.  My
installer proposes to have the sheetrock installed except for a 12" gap
at one end of the ceiling, and cover that with a net, then blow
cellulose into the space from one end.  I'd like to have about 14" of
cellulose when I am done. Does that sound reasonable? So you can't dense
pack it, because the space is too deep.  It is bound to settle, because
it isn't dense packed.  How will they know if they are applying the
right depth of insulation?  

--Lawrence 

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of George J.
Nesbitt
Sent: Thursday, July 27, 2006 1:59 PM
To: Greenbuilder list; George J. Nesbitt
Subject: [BULK] Re: [Greenbuilding] Cellulose settling/blowing
Importance: Low

So as a "Professional" installer of cellulose I have the following to
say about cellulose settling.

If you look at a bag of loose fill insulation (Cocoon) for attic
installation you would blow it in at 1.4 lbs/cuft density to a depth of
12" to achieve R-40, and it would settle out to 10.8". Settling is not
an issue for attic insulation as long as your final thickness is the
minimum (otherwise you blew it at too low of density and didn't achieve
your R-value).

For wall installation you install it at 2.6 lbs/cuft, R-13 with 2x4,
R-19 with 2x6 (retrofit Cocoon dry pack installation). If you follow the
manufactures specifications for walls you will get settling. Typically
(hopefully) this is installed using 1-1/2" holes not more that 4' apart
(vertically) in every stud bay, and the nosel is stuck into the hole and
the wall is filled. You might not get around every obstruction and the
density will be greatest near the hole. I have opened walls (on my
parents house that I had filled by a subcontractor 10 years before) and
found a large gap at the tops of the stud bays (holes at bottom of wall)
either from settling, or not fully filled. When you have a gap in
insulation it has an effect far greater than its area. So a 1 or 2% gap
reduced the insulation value 15% or so.

There are two reasons for dense pack cellulose, 1st is to eliminate
settings, 2nd to reduce air infiltration. Dense pack requires that you
install at 3.5 lbs/cuft or greater density (I have read that 3.2 is ok,
but probably about the minimum). Because some of the fibers in cellulose
are very fine, it fills some of the holes in the walls. When you do a
blower door test to measure the air leakage in a building before and
after retrofitting walls with cellulose you will see a measurable
reduction in air leakage (even at lower densities). If you blow in
fiberglass you will not see a difference. So how do you install dense
pack cellulose? you use a bigger hole, 2 to 2-1/2", one per stud bay,
you insert a 1 or 1-1/4" interior diameter stiff vinyl hose up the wall
(drilling from the bottom seems to be the best method) and fill the wall
removing the tube slowly to prevent clogging the hose.The equipment you
get from Home Depot, or Lowes, or a rental yard is typically not
powerful enough to get this density. I have a 20yr old Force 2 blower (I
got it free, $5000 new), but I am only able to get up to 3.2 lbs with
this method (I don't use a vinyl hose yet, might help), it only has one
blower, a machine with 2 blowers is probably the minimum. Don't assume
you installer is doing dense pack, I don't know anybody in my area that
does it other than me.

Cocoon 2 Stabilized Borate Formula for wet spray installs at 2.6
lbs/cuft, but because of the glues settling is not an issue as far as I
know. If you add to much water it doesn't fill around obstructions as
well. I just learned that the glue is either gar gum or wheat, I have
problems with gluten (contained in most grains) and need to find a
supplier of borate only, no glue cellulose insulation.

I haven't done any blow in batt (netting) jobs, but I suspect that you
can't blow it dense pack without blowing out the netting, or interfering
with Sheetrock unless you strap the walls. An alternative method is to
hang the rock and dry blow dense pack after, but before finishing taping
and mudding, if you want to avoid wet spray.

I have herd good things about Johns Manville Spider spray in fiberglass,
formaldehyde free, although it probable has an acrylic binder.

The problem with batts is they are typically installed poorly. Gaps top
and or bottom, compressed in width, don't fill the depth of the cavity
fully, gaps because not cut around electrical wiring, plumbing,
blocking, kraft faced batts create a gap at the Sheetrock that allows
convection currents (even if you face staple and don't inset staple so
the sheetrocker can find the studs).

You will almost always get better quality from a blow job than from
batts, even if you get some setting on average it might be better than
the average batt job. The best batt job is still 10% worse than a spray
blow in job.

Keith Winston wrote:

>Hi  Jefro,
>
>Many, if not most, cellulose suppliers will supply, often for free, a 
>blower when you buy a lot of cellulose. Beware: the cellulose to fill 
>your entire 9.25" wall for an entire house will be a LOT of cellulose.
>You should look to get it delivered. In which case you might have to 
>rent the blower separately. Which may not be a bad idea, since the 
>rentals are sometimes better units.
>
>Lowes often sell cellulose around here (Home Depot doesn't), and 
>they'll give you a cheap rattly little blower. BUT: at one of their 
>stores, they have a trailer they'll rent you for $40/day, with a REAL 
>blower in it (and enough room for a fair bit of insulation, but still 
>only 1/10 of your whole house, probably). You have to make sure you can

>park the trailer close enough that the hoses will reach everywhere you 
>need to get to. Otherwise, most freebies and rental units are portable,

>and can be rolled into position (some are heavy, mine is around 200 lbs
I think).
>
>A medium-sized house might take a 40' trailer of cellulose. Have at 
>least 2-3 assistants for blowing, it'll go easier. You probably won't 
>have a recycler (a big vacuum) so someone will be hauling bags of 
>overblow back out to the truck/blower regularly.
>
>Keith
>
>Jefro wrote:
>  
>
>>Does "DIY cellulose" mean renting a blower and installing cellulose 
>>into cavities on one's own?  I didn't know that was a possibility.
>>
>>We are building a home this fall using cellulose inside a 9-inch 
>>cavity built from a 2x10 plate and a double 2x4 wall.  We have been 
>>planning to find an installer to use wet-blown cellulose.  I am very 
>>interested to hear about other options, although I do have concerns
about settling.
>>Please continue to discuss!
>>
>>thanks
>>
>>
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