I have been remodeling my house in Syracuse, NY. My county is on the line of zones 5 and 6 in central NY.  Over the last few years I have fell in love with building science while working in the trades, and am working to improve my paid off house. 

I have a slab on grade 2 story house, 2×4 wall construction on a 1′ stem wall, truss roof with a vented attic. I am planning to install an erv this winter while I have down time.

I recently have ripped the outside down to studs, filled the wall cavity ( previously not insulated) with fiberglass r-15 batts with paper facer facing the interior, and covered the walls with zip system. I have either taped, gasket, or liquid flashed every penetration and have liquid flashed to the stem wall. Every window has been replaced with new flanged Anderson windows, these have all been exterior zip taped and backer rod or expanding foam/ pro clima taped to the framing on the inside.

Code for insulation is r13+continuous r10 exterior as I understand it for walls.

My primary question is whether I cover the exterior with paper faced roofing polyiso ( I work in commercial roofing, and have access to it at a very good price point), or to install a smart vapor barrier and add wall thickness on the interior as a double stud wall of sorta with the smart vapor barrier being applied to the existing wall before adding the next insulated “service cavity” wall. It seems the polyiso is the cheaper, quicker, and easier way to go. I am very concerned with condensation from vapor. I have read and researched lots on the site to get me this far.

My next question is strategy for my attic. It is currently insulated between rafters aigh a loose fill insulation. I was planning to apply an exterior smart vapor barrier over the top of it, and install more insulation above it. Doing this would save me from tearing down ceiling sheetrock, and would make the drywall airtight lid less critical as I understand it 

Any direction would be great here. Thankyou ahead of time for looking!

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