Rain Screen Needed for Vertical Metal Siding? – GreenBuildingAdvisor

Hello All!  I’ve read through many posts about metal siding and the need for a rain screen product (like Cor-A-Vent or whatever) or not.  One post indicated that code in BC is that if 8% or less of the siding material is touching the substrate, and has a drainage plane, that counts as a rain screen.  Other posts say that vertically installed corrugated metal, as long as the bottom and top channels are perforated, is fine (corrugated seems like much higher than 8% touching).  

We are looking at a vertically installed reverse board-and-batten type design, with only the fastener and locking strip touching, but it’s still more than 8% contact (maybe more like 15-20%).  I’m still picking the exact product, but the depth of the siding might be as shallow as 3/8″ and as deep as 1″ — but definitely enough for good airflow and drainage. [I haven’t yet found a perforated channel that is wider than 3/4″ but the hunt continues].

We’d like to avoid adding a rain screen if it’s really not needed.  Back-of-envelope calculation for Cor-A-Vent is like $10k in materials and labor (labor mostly, as we have a LOT of wall), and we are so far over budget it’s painful, so if it could be safely skipped, that would be great (safely being the operative word there).

Does anybody have any advice or concerns about skipping the formal rain screen and using perforated J/L channel for this type of siding?

Thanks so much!!!