I drive past a lot of new construction sites regularly since they have been building about 200 houses a year in my town.
I see the roofs dried in. I see the ice barrier on the eaves, then the felt on top of that. This is good.
I also see felt up to dormers, skylights, chimneys, etc. , with ice barriers at these locations. Then I see the shingles being installed OVER the ice barriers. They never get tucked under the ice barrier at the lower courses.
By doing this, if the ice barrier is called upon to do its job, which is to protect against ice backup and infiltration, when said ice melts, the runoff will flow behind the shingles. This is the part that leaves me scratching my head and asking WTF?
Good roofing practice would dictate that the ice barrier be configured to drain out of the roofing system (on top of shingles) instead of behind it (under the shingles). Does this help to clarify? If not, let me know.