"Greg O" wrote in message
...

"effi" wrote in message
...
would like to create a cathedral type ceiling in a small area of 24" on
center roof rafters 3.25" thick

within the 3.25 inches thick want: 1" airflow space; and 2.25" insulation

how can the 1" thick airflow space (between 2.25" insulation and
underside
of roof decking, plywood) be created?

seems just putting 2.25" thick of insulation without some means to keep
the
1" airflow space open might be a mistake



Seems to me that 2.25" of insulation is a mistake!
Greg

ya, am leaning towards 4" of glass compressed into the 3.25" space, with
perforated pvc pipe run centrally through it for air flow

hardie panel soffit board will be ceiling and provide some insulation factor
as well