I am working on an addition that attaches to the side of the existing house.   The original building has a vented attic built with high heel trusses and a vented soffit.  Along the side of the original exterior wall, I’ve removed the facia and soffit and then tied the new rafters into the old tusses.  The new roof sheathing will now meet the old sheathing so I will have a continuous roof plane.  The new roof is a hot roof with 2×8 rafters.  I have no issues insulating the rafter space and sealing the entire roof assembly, with the exception of the 8 inch space where the two roofs meet.  Do I need to seal that gap with foam or some other vapor barrier, or should I fill the gap with batt insulation allowing some drying into the attic space?