[Greenbuilding] insulating on sheathed roof

[RH Irving Co Inc.]

Robert
Sounds like you are comparing apples & oranges.

"wet-sprayed" cellulose is not the same as dense pack cellulose.  "Cellulose
insulation (spray on)" sounds like loose spray (like into an attic). 

Did they test DRY dense pack?  At what density?
Bob Irving

-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Robert Tom
Sent: Thursday, January 03, 2008 3:47 PM
To: greenbuilding at listserv.repp.org
Subject: Re: [Greenbuilding] insulating on sheathed roof

Prior to the Listserver [BURP] before the holidays, and now that the  
archives are accessible someone wrote:

>> Why do you say blown cellulose requires no vent space?

> dense packed cellulose stops almost all air leakage,where as fiberglass  
> needs venting

The above seems to imply that dense-packed cellulose functions as an air  
barrier, a myth that was previously promulgated on this List years ago by  
a Frank Lugano who used to (and perhaps still does ?) write as a "  
weatherisation expert" for Fine Homebuilding magazine.

If no vent space is required in a cathedral ceiling it will be because the  
air barrier strategy is effective.

Dense-packed cellulose is *not* an air barrier material.  " 
In 1985, the Canadian building codes recognised that building assemblies  
needed to have an effective barrier to limit air infiltration/exfiltration  
in order to avoid the moisture problems that result from bulk moisture  
transport via air leakage.

In 1988, an external research contractor for CMHC undertook a project to  
evaluate the air impermeance of some common building materials and the  
results of that testing were published in the CMHC report "Air Permeance  
of Building Materials". That ~12mm-thick report is free to all Canadians  
and for a nominal fee to others, from CMHC.

 From Table 6 of that report, the IRC (Institute for Research in  
Construction at the National Research Council of Canada) classification  
for air barriers systems is:

	Type I : max air flow @75 Pa = 0.15 L/s-m^2)
	Type II: 0.10
	Type III: 0.05

Table 8 in the above report lists the effectiveness of the materials in  
descending order and among the materials tested were fibreglass batt  
insulation and wet-sprayed (ie dense-pack) cellulose .

Glass wool insulation is third from the bottom in the table, with average  
air flow (Q-avg) listed as being 36.7327 L/s-m^2 @75 Pa.

Cellulose insulation (spray on) was last in the table, just below  
vermiculite, with Q-avg listed as being 86.9457 L/s-m^2 @75 Pa.

Neither fibreglass nor cellulose were sufficiently air-impermeable to  
achieve a rating.

To be fair, it should be noted that the glass wool insulation tested was  
152 mm (~6") thick and the cellulose thickness was only 38 mm (~1.5").

I'll leave it to interested parties to do the arithmetic to determine  
effective air permeances for the specific thicknesses that they are  
considering.

			=== * ===

And speaking of listserver [BURPS], I sent out the following message  
almost immediately after reading Duck Foo'd's message about the impending  
Listserve maintenance/potential disappearance but apparently it was too  
late to get distributed by the Listserver.


================ Forwarded Material ===================================
On Fri, 21 Dec 2007 11:03:02 -0500, Robert Tom <ArchiLogic at yahoo.ca> wrote:

> Duck Foo'd wrote:
>
> [snipped & pasted]
>> server migrationThere may be delivery delays and other burps, including  
>> a total vanishing act
>
> Recalling the last time that the GB List disappeared, (the last time we  
> did not have the benefit of a warning -- thanks, Mark for this one) I've  
> just done a few mouse clicks to create a surrogate GB List just in case  
> there are unforeseen glitches in the migration process and the down time  
> gets extended to a period of weeks or months.
>
> http://groups.yahoo.com/group/GB-r-us/
>
> If anyone would care to become the defacto List Owner, drop me a line.
> S'awright ? S'awright.
============ End of Forwared Material ==================


The above back-up is in existence and can be in place for future [BURP]s.

If anyone does subscribe as insurance for the future, I would suggest  
opting for the
"NO EMAIL" mode of mail reception until such a time as this Listserver  
does go down and the backup is needed.

I also noted that this List' archives were completely inaccessible (ie  
non-existent) during the down-period. Perhaps what might be done is CC  
messages to the back-up GB list so that in the event of a failure of this  
Listsever, there will still be an accessible archive.


-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at chaffY a h o o  dot  c a >
manually winnow the chaff from my edress in your reply


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