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

George J. Nesbitt george at houseisasystem.com
Thu Aug 22 14:49:03 CDT 2013


     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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