[Greenbuilding] insulating on sheathed roof

[Robert Tom]

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