[Greenbuilding] [BULK] Re: vented roofs

[Lawrence Lile]

I think the conspiracy theory holds some water.  The thing that the
fiberglass companies are embarrassed to say is, their insulation wimps
out at low temperatures - the R value actually drops when the
thermometer drops.

I can speak to the vented cathedral ceiling idea. It is not difficult to
do at all.  I've got a cathedral ceiling made out of 24" trusses, and
plan on using cellulose.  Despite some strong arguments on this list, I
could not be convinced to install a "hot roof" nonventilated attic.  I
still don't know if I made the right choice, but that's how we are
building it.  

The insulation contractor plans to install insulation screen, then blow
cellulose above that.  It won't be dense packed, so it will settle some,
but we should be able to pack 18" in there easily which will be plenty
after settling. Gyp board goes on when they are done.  No vapor barrier
on the interior. I have been very careful to avoid any penetrations in
the ceiling gyp board, no ceiling can lights and such, and have been
caulking up little things like electrical penetrations in the top plate.
There should be very little air movement to transport bulk moisure into
the attic. 

We could have done the same thing with a 16" truss and a hot roof
design. Either way, I don't think it is hard to do.   
 

--Lawrence Lile, PE, LEED AP
Project Solutions Engineering www.projsolco.com



-----Original Message-----
From: greenbuilding-bounces at listserv.repp.org
[mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Laren
Corie
Sent: Saturday, September 16, 2006 2:21 PM
To: greenbuilding at listserv.repp.org
Subject: [BULK] Re: [Greenbuilding] vented roofs
Importance: Low

"Janet L. Hobbs" <janethobbs at hobbsink.com>

>  I have heard but not verified that some shingle manufacturers won't 
> warranty their product if it isn't ventilated.

Hi Janet;

  That is true;

 They say that heat is the reason for the invalidation of the guarantee
However, it is very interesting that testing shows that darker shingles,
over vented attics, consistently run much hotter than lighter colored
shingles with no venting.  That reason is not logical.

So, there must be more at play here, than is first apparent.

1) The big shingle companies that set the standards, are also the major
fiberglass insulation manufacturers.
2) The unvented roof insulations are the same insulations (cellulose and
foams) that are major competition to fiberglass.
(if 8-9%, in the US, can really be called major competition)
3) The fiberglass industry has an extremely well organized program to
dis-educate the public against alternatives.  Just Google "cellulose
insulation" then look whose pages come up, and how most of them use
identical extremely well written, but even more deceptive, text from
their insulation manufac- -turers association, that only allows
fiberglass manufacturers.

   The limit on the warrantee is a very clever way to get two advantages
at once  They can both get out of their guarantee, while screwing up a
good sale for their insulation competition.
Cellulose is, by far, the main competition. Vented cathedral ceilings
with cellulose are generally too much bother to be cost effective.

That seems to be the only understanding that makes full sense.
If anyone has contrary information, please present it.  I would hate to
be seeing evil, where it does not exist, but nothing else seems to be
logical, in this case.  Their fiberglass industries'
cellulose websites are definitely in a category that I consider
immorally deceptive.  They have some very good writers, who could
convince you to stop breathing to avoid second hand smoke in the middle
of Antarctica,

-Laren Corie-
Natural Solar Building Design Since 1975 www.LarenCorie.com

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