Insulating a cathedral roof with rigid foam
I for one like the new spray-in foam.  It does such a good job because it makes the house so tight. Infiltration is where you loose your heat.  It's the cracks that hurt you.  Nothing seals the cracks like the spray-in expanded polystyrene.  Regarding all that venting business;  they are just trying to keep the roof surface cold so the snow won't melt and cause ice dams.  Nothing out there can better keep the heat away for the roof surface.