We are building a home in CZ 6.  Part of the volume is a single story enclosed with a 13:12 cathedral ceiling.  The construction will comprise a vented assembly with fibreglass batts and interior rigid foam (similar to ‘Assembly #2’ in Martin Holladay’s ‘Five Cathedral Ceilings That Work’ musings dated December 11, 2020).  We have run into several potential blockages in the continuous air channel in some of the bays.  One is a shed dormer partly up the roof that could block the top of the channel in the affected bays.  The other is a valley flashing that threatens to block the bottom part of the channels that start at the valley.

These details occur in many builds.  I am curious how they are resolved.  Any ideas would be appreciated.