Is it unnecessary to ventilate my roof?

(See revision below...)

I am an owner/builder and I am only part way through the process of learning everything I need to learn to manage my upcoming laneway house project, or ADU as we say here in BC. I am in the midst of designing my roof system. I am going to make a bunch of mistakes, so please bear with me.

The immediate issue is that I am mystified by the following provision of the BC building code:

>9.19.1.1. Required Venting

>Except where it can be shown to be unnecessary, where insulation is installed between a ceiling and the underside of the roof sheathing, a space shall be provided between the insulation and the sheathing, and vents shall be installed to permit the transfer of moisture from the space to the exterior

I don't get the logic of this at all. It seem to me that this conflicts with the concept of sealed house. We go to all the trouble of keeping our energy tightly inside, then let the wind blow it all away through the roof? And worse, we provide a large cavity for wet, stagnant air to sit inside to cause mold and rot? At least, that is what I think will happen up here in the rain forest.

I think I want to rely on that "where it can be shown to be unnecessary" provision. Here is my counter proposal:


So here is where I sit back and try to dodge the tomatoes that I no doubt deserve to have thrown at me for proposing a roof system with no obvious path for moisture to be carried away. Actually, going inside to out, everything should be fine until the escaping moisture hits the standing seam panels and gets trapped there.

How do I fix this? Short of going back to what I perceive as the outmoded notion of whole-roof ventilation, starting at the eaves and ending at the ridge vents. I kind of think that ridge vents should not be a thing any more in this modern era of air-tightness.

(edit) Thanks for the great commentary! I have not yet responded to all, but I will. In the mean time I have incorporated what seems to be the general consensus into my roof section drawing. TLDR: While I may not *need* exterior roof ventilation, I will probably benefit from it.

Longer version: exterior ventilation in the form of furring will help prevent ice dams. There may be other benefits. In addition to adding vertical furring under the standing seam panels I will require a ridge vent (customized version of a standard standing seam ridge flashing) and some special treatment at the eaves (to be determined). I have tentatively settled on 16mm (5/8th!) plywood strip furring which might be a bit on the slim side according to one comment, so that needs to be looked at critically from an air flow point of view.

Revised roof section:


Some details still need to be settled but it seems that this design has progressed in a useful direction, so thanks all for the help with that. No doubt there is more discussion to come. After all, we have only been building sealed houses for thirty years, right? Still in flux.