Originally Posted by
Rick Cantrell
Yes, to prevent water from getting under the shingles the flashing must always be on top of the shingles.
As I said above, 'not must'. There are areas where that is just asking for trouble.
In the hurricane prone regions of South Florida, the flashing is sealed down to the underlayment, then the shingles are sealed down to the flashing.
NO LEAKS.
And, the flashing is not exposed to high winds, which could (would) rip it right off the roof if they were on top and left exposed, which would then lead to loss of the roof covering system.