[Greenbuilding] blown-in cellulose: theory behind two holes per cavity?

Reuben Deumling 9watts at gmail.com
Fri Aug 23 01:44:23 CDT 2013


Success! 3.6+ lbs./cu ft.

I upped the blower speed and took a more aggressive approach: *stab and
retract*.


On Thu, Aug 22, 2013 at 12:49 PM, George J. Nesbitt <
george at houseisasystem.com> wrote:

>      So, densepack cellulose is supposed to be 3.5# ft3 or greater. 3.2#
> is probably ok for 2x4 walls. I saw a chart (from denmark) at the 2012 ACI
> conference in Baltimore. It showed that as a wall got thicker (2x6, 2x8
> etc.) that you need a higher density to prevent settling. Excessive height
> would likely require greater density too.
>     At 2.4# ft3 you are way too low, using 2, or more holes may get you a
> little extra density. But the problem is that your machine does not have
> enough umph. You need a minimum of 2.9psi or 80iwc of pressure at the
> machine outlet to install densepack. You may need to replace the airlock
> seals, or completely rebuild the airlock.
>     My 20 year old force2 with a rebuilt airlock and a new blower can now
> do densepack, but the newer machines have more powerful blowers (and some
> multiple) and can do it faster & easier. Intec's new Turbo Force HP can put
> out 6.9psi!
>
>
>
>
> On 8/21/2013 10:32 PM, Reuben Deumling wrote:
>
>    I'll admit I'm not a regular at this task. To date I've chiefly blown
> cellulose into open cavities from the outside. It worked great and I
> achieved the desired 3.2+ lbs./cu ft without any heroics.
>  Now I'm blowing cellulose into somewhat odd-shaped cavities that have
> plywood faces on the inside and out. The cavities, as mentioned here
> recently, are about 5' tall and 10" thick with plywood gussets connecting
> the interior 2x6 walls with the exterior 2x4 walls. These knee walls
> project out beyond the 2x4 walls of the house above, leaving a convenient
> shelf on top through which to drill 80 holes and blow insulation. So far so
> good. But so far I'm only achieving about 2.4 lbs/cu.ft. I inserted my
> flexible 1.5" vinyl hose to the bottom of the cavity and retracted it as it
> filled/stopped blowing. My ability to move the hose about at that extension
> is limited however, and so I'm not really that surprised that the desired
> dense pack density has remained elusive.
>
>  So my question: would it make sense to drill a second set of holes near
> the bottom and attempt to blow more into the ~lower third of the now
> partially filled cavities? I'm not clear on the purpose of having two holes
> per cavity. I am assuming it allows the hose to reach more places within
> the three dimensional space and therefore achieve higher density, yes?
>
>  The mesh I stapled between the cavities is working quite well to allow
> the air blown in to escape/depressurize the cavity.
>
>  Thanks very much for any insights.
>
>  Reuben
>
>
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>
> --
> George J. Nesbitt, Environmental Design / Build, Building Performance
> Contractor, HERS I Verifier & HERS II Rater, GreenPoint Rater new &
> existing SF & MF, CABEC CEPE (Certified Energy Plans Examiner), Certified
> Passive House Consultant, BPI Multifamily Analyst, www.houseisasystem.com,
> (510) 655-8532 office, (510) 984-8344 mobile
>
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