I can't speak to shingle life, as the homes we've done have had alternative roofing materials. 2 had metal roofing and 1 had synthetic slate (plastic). That said, all three had ice dam issues. 2 of the homes were cape style so even where the only insulation space is the remainder of the rafter cavities we found the system resolved all icing issues so I think it would work great with cathedral style ceilings.