Venting open web floor Joists as rafters on a monoslope roof in maine. – GreenBuildingAdvisor

I’m looking for the most durable and practical assembly of a shed style mono-slope roof without spray foam. I understand the topic of venting and insulating cathedral ceilings has been addressed here many times but I have one assembly that I would love the experts’ opinions on.

The assembly is a 3/12  shed style roof in climate zone 6 in Maine.  The proposed assembly is as follows:

Inside to Outside. 

1/2 Drywall and strapping

Intello SVR taped

3 1/2 in by 16inch open web floor joists for Rafters, I’ve worked on a project that used I joists and I figure the open web may be better for thermal bridging.

Dense Packed Cellulose

Tyvek Commercial wrap stapled on top of the rafters to create vent baffle

2X4 Furring on top of Open Web joists to create air space for vent channel.

Roof Sheathing.

Standing SeamMetal Roof.

Like I said before I  have worked on houses before that used I joist rafters in a very similar situation but all were sprayfoamed.  I wanted to avoid the use of spray foam and still have a very durable assembly. Is 3/12 too poor for  venting?  Should I create a deeper air vent channel?  I know exterior insulation would be best but with the proposed rafter spans and insulation ratios I would need almost r 40 above my roof deck if I used a 12 Inch I joist rafter filled with cellulose.   Thanks everyone for your input!