Is it okay to insulate an unvented conditioned attic using a hybrid of approaches?  Specifically, under the roof, we plan to use a flash-and-batt approach (because we are unable to install exterior insulation above the roof).  However the gable walls will have exterior foam up to the roofline.  I do not want to use spray foam against those gable walls in the attic and form a dreaded “foam sandwich” with the sheathing there.  So do we insulate the gable walls in the attic just like we do in the living areas of the house, where we will likely use dense-packed cellulose?  (We live in climate zone 5.)  Presumably we will have to cover all insulated surfaces with an additional gypsum board or whatever our code requires, but under that cover would be different insulation approaches.

Judy