On Wed, 10 Dec 2003 17:46:00 +0000, a particular chimpanzee named
Johan randomly hit the keyboard and produced:

So why is it not possible to put insulation between the rafters, and
then seal the warm side with a vapour barrier, and not have any
ventilation?

In my particular circle of Hell, Beelzebub will be tormenting me for
all eternity by asking, "why do I need to ventilate my roof?"

A vapour barrier will not stop all moisture from penetrating into the
void above the insulation. Even with the best workmanship, it's still
going to be punctured by nails and electricians. As the insulation
does not cover the tops of the rafters, condensation can occur in
them.
--
Hugo Nebula
"You know, I'd rather see this on TV,
Tones it down" - Laurie Anderson