Vapor diffusion port at edge of mono slope cathedral ceiling – CZ3 – GreenBuildingAdvisor

After going down the rabbit hole on cathedral roof/ceiling details I’m almost ready to commit to an air permeable insulation approach between rafter bays while utilizing a vapor diffusion port. My reasoning behind this decision is that I would like to avoid any spray insulation for health and environmental reasons. An alternate approach would be a layer of exterior rigid insulation with mineral batt insulation against the underside of the roof deck. From a labor and material standpoint though, I like the simplicity of the vapor diffusion port approach. 

All that said, I’ve not seen many VDP details beyond utilizing a typical ridge vent. My project has a mono slope roof and I’m curious to know if there proven methods for introducing a VDP detail at the high edge of the roof? 

Any advice on the detailing of the edge VDP or to redirect me toward another cathedral roof/ceiling assembly would be greatly appreciated.