"Greg" wrote in message
...
Where do you live? It makes a difference on where your vapor barrier goes.
If you are someplace where you run the heat more than the A/C you want the
barrier on the house side. That is where the warm moist air comes from,
the
attic is cold.
If you are in Florida you reverse that. The warm moist air is in the attic
most
of the time and the house is cold. Water forms in the insulation if you
don't
have the barrier on the top. It will turn your cellulose into grey mud
that
eventually just rots to clumps of dust.
Want some, I have an attic full. I will mail you some.

Makes sense.
Here where our climate is probably similar but somewhat colder than say New
England, the rule is that a vapour barrier should be on the warm side of the
wall; e.g. plastic sheet under the wall and ceiling plasterboard. And at
most not more than one third (33.3%) of the way through the wall from the
warm side.
But that is for a 'cool' maritime climate where, without a vapour barrier,
the danger is house moisture permeating out through the wall and condensing
into water within the insulation making it wet, ineffective and with
potential for mould and rot!