[Greenbuilding] insulating on sheathed roof

[Ted Inoue]

There have to be more problems with methodology.
First, since when has fiberglass had any resistance to air flow? You put
75Pa across fiberglass and I guarantee that you're going to see more than
37L/s-m^2 unless it's something like a DensPack Gold.
Second, you have to consider the use. A dense packed cathedral ceiling is
stopping air from moving through the cavity, which may run several meters.
Except right at the soffits and at sheathing joints, you're not having air
pressure perpendicular through the cavity (i.e. the thin aspect of the
cavity).

Note that I'm not making any claims regarding the actual performance of
dense pack in this application. My intuition is that the performance is
better than these studies indicate, and much better than fiberglass, in any
case. In fact, I'm tempted to try my own study to measure the performance of
several insulations under different conditions.

On Jan 3, 2008 5:29 PM, Bob Korves <bkorves at winfirst.com> wrote:

> ----- Original Message -----
> From: "Robert Tom" <ArchiLogic at yahoo.ca>
> To: <greenbuilding at listserv.repp.org>
> Sent: Thursday, January 03, 2008 12:46 PM
> Subject: Re: [Greenbuilding] insulating on sheathed roof
> (snip)
> > 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.
> (snip)
>
> Hi Rob,
> I totally agree with your conclusion that dense pack cellulose is not an
> effective air/vapor barrier.
>
> What I have a problem with is the fact that the Canadian government test
> results are listed in six significant figures.  Anyone who has taken a
> quantitative analysis class would know immediately that this sort of
> testing
> is not reportable to six significant figures.  If a group reporting
> quantitative results does not understand the process of quantitative
> analysis then I suspect that the findings of that group may have other
> problems as well.  Possibly not, but visibly shoddy work...
> -Bob Korves
>
>
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