New build: need roof insulation advice

[sco44]

Not quite to the insulation stage, but want to figure it out now. Have a build thread in garage gallery

The building is a Websteel, vaulted truss and clear span. 12-14' spans between truss/columns. The purlins are 2x8 on edge parallel to ridge.

Websteel recommended using condensation blanket. So 2-3" fiberglass (r8 or so) with vinyl backing was layed over purlins and then the metal sheeting. The ridge and Eve edge of panels are sealed using the foam contoured closure strips (no venting). The vinyl backing is faced down per the instructions.

I hadn't thought as far as finishing off the insulation on the inside. I would like to finish off with batts if possible. And I have room for a decent r value. But should i be using a vapor barrier over my batts on the inside? Or would this be creating a double vapor barrier trapping moisture?

I don't want to "sheet" the ceiling. But am looking to cover with something white/ reflective.

Walls are 2x6 on edge and exterior has house wrap. Planning on r-19 batts but should I be running interior vapor barrier? I have heard yes and no. I am climate zone 4c..

The building will have radiant floor heat.

Any info would be great!

Thanks, Scott

 

[Randy in Maine]

Have you spoken with the "spray foam" guy? You should.

 

[sco44]

Not yet. Was hoping to be efficient enough without that option lol.

I could potentially look into closed cell on just the ceiling, maybe 4" or so. Walls I will be fine with r19 in my climate. Just undecided on interior vapor barrier.

-Scott