In northern Ohio, have a 1.5 story cape, with three dormers.  Two dormers on the front and one on the rear of the house.  I can get into each knee wall section.  Although I don’t know how to seal this inside that bay.  I have a ridge vent, but no soffit vents.  I think I can do polyiso inbetween rafters, and put in my own soffit vents.  I think I can slide polyiso into the sloped part of the bays, from inside the knee wall while maintaining a vent channel.  Rafters are 2×6.  But how do I deal with the dormers?  There’s a tiny little triangular section of roof in front of each dormer too.  I can see it from inside the knee walls, but doing anything there seems unlikely.

Other details: The topmost attic is accessible, but too small to slide anything down into the rafter bays.  There is a large amount of blown in fiberglass up there already, so that part is all set.