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GBlist: re:Dense pack and diffusion
on Sat, 03 May 1997
Lugano@ix.netcom.com wrote:
re: Dense pack and diffusion
[ Insulation 101 <snipped>
> It's the *huge* moisture storage potential that DP imparts to a wall
> assembly... more is better.
> Well, [dense pack cellulose ] provides the most, and this has been
> demonstrated to be a big factor in protecting the walls and
> building durability into the finish systems. Houses insulated in the
> '20s with cellulose in Saskatuan (12,000 DD) had perfectly preserved
> wall assembles when studied in the late '70s during demolition. It is
> the only insulation material that has a this kind of track record,
Hello CelluloseHeads;
Apologies in advance for a post that will have very little (none ?) of a
positive nature to contribute, but I felt compelled to respond to the above
claims. Before going any further, I'd first like to emphasise that I think
that Dense-Pack Cellulose is a superb, Green-ish insulation material with
admirable performance qualities.
However, in view of the fact that water is an excellent conductor, I fail
to see how large amounts of moisture stored in a thermal insulation
material (ie that which seeks to minimise the conduction of heat) could be
considered a "good thing" as Fred seems to suggest.
On a another point:
I'm not familiar with the 1920's houses in Saskatchewan that FL is
referring to ...(it's a BIG province ranging from the 49 to 60 deg N
latitude and about 850 miles long x 350 miles wide eh ? and "yeah" I looked
at a map)... but I think it's safe to assume that like most houses of that
era, they were probably leakily-constructed, minimally-insulated structures
...and like most buildings of that ilk, there are seldom any instances of
moisture problems due to exfiltration leaks or diffusion.
On a nit-picking point : Most of the population of Saskatchewan is
concentrated south of Prince Albert (11430 HDD/yr)... and 10,800 HDD/yr
(rather than 12,000 ) would be more representative of the climate that most
Saskatchewanians would experience.
On another nit-picking point: It's incorrect to say that cellulose
insulation (in the form that Fred is referring to) is the _only_
insulation with a stellar track record.
There are baled fibre (hay) houses in the Sandhills of Nebraska (~7000
HDD/yr) that were built earlier near the turn of the century. Some of those
houses are still inhabited. Examinations of some of those structures have
revealed no moisture problems.
The thick walls of such structures would provide insulation levels that
would be equivalent to, or in excess of, what we consider to be
"superinsulated" these days and would seem to provide a more relevant
indication of the consequences that what one might expect of unrestricted
moisture migration.
However, like Saskatchewan's climate, that of northern Nebraska it is VERY
dry and moisture accumulation is seldom a problem. (It is probably for this
reason that early descriptions of the area by Lewis & Clark et al referred
to it as "The Great American Desert".) Like the Saskatchewan examples, the
Nebraska homes would provide a multitude of escape routes for moisture.
As such, I would suggest that the Saskatchewan (and Nebraska) homes would
be far from being indisputable evidence of the benefits of a particular
practice (ie whether or not to include means to minimise vapour
diffusion/leakage) or the superiority of a material's performance.
I'm afraid I have to agree with Marc (the Bumbling One) who said earlier
on that we've had a great heap o' Insulation Contractor Hyperbole (ICH)
piled onto us.
--
Rob Tom
---------- * ------------
be417@FreeNet.Carleton.ca
Kanata, Ontario, Canada
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