Pop wrote:

... being "international" I couldn't find anything in my quick
research that would show it to be applicable to anything but
commercial construction regs... It's the same place that said...

"a) Attic furnaces and crawlspace furnaces are not permitted. "
but, what's missing there is the fact that they ARE permitted,
just under a different section and with caveats. But, this isn't
the point here; the next one is:

"d) All dryer vents shall be metal or metal flex. Non-metallic
vents for dryers are not permitted. See Section 504.6 and
Amendment to 504.6 "
Soo, the flexible, nylon-wire-ribbed parts sold in stores with
UL and CSA ratings, even ETL probably, and EC, aren't allowable?
I respectfully submit that they ARE permitted...

And then:

"All ductwork shall be a closed system and in compliance with the
International Mechanical Code Section 603. Use of a stud space or
joist space for a supply or plenum return is not permitted.

This reminds me of the National Mechanical Code, which is said to
prohibit circulating conditioned air at more than 120 F in wooden
stud spaces. I presume the excuse was the danger of fire, and the
code committee creatures who wrote this sell fireproof materials.

A few of the few dozen wood solar attics in Soldiers Grove WI were
lined with drywall after the state declared them "plenums," until
pharmacist Don Stebbins refused to do so, saying the theoretical
graph they were using for the time it takes wood to catch fire was
in degrees C vs F, and the time scale was log vs linear. At this
point the state creatures cravenly slunk away without reimbusing
the injured parties. There have been no fires in 27 years.

"Gypsum ducts are not permitted. Delete Sections 603.5 and 603.5.1."

Good thing the code creatures didn't see that part :-)

Nick