[Greenbuilding] insulating on sheathed roof

[Alan Abrams]

<Foams and dense pack cellulose, that
will not leave an attic space below the roof deck, do not
require venting>

Any studies or information on whether cellulose slumps away from the
underside of the roof deck over time--leaving a gap for moist air to
accumulate, and condense on the sheathing?

Alan Abrams (who uses foam so as not to worry about this)