Re: Tar paper vapor barrier?
Your tar ( or felt ) paper is not considered a vapor barrier.
Materials having a permeable rating of 1 or lower is considered a water vapor barrier .... tar ( or felt ) paper has a permeable rating of 5 or higher which means the interior vapor within the walls will breathe outward.
It's intended purpose is provide a barrier to protect the sheathing from liquid water also to assist with being an air barrier.
You might consider using blown in cellulose which works fine for your application.
"" an ounce of perception -- a pound of obscure "