I am building a cabin in Tennessee with exposed 4×8 rafters and 2×6 T&G decking. The walls are 2×6 with 1″ zip-R sheathing. There is a layer of weatherguard air-barrier OSB on top of the 2×6 decking. All the seams are taped. On top of that I will have three layers of 2-1/2″ reclaimed polyiso foam, seams staggered.  I will have roof extensions to create overhangs screwed through the OSB and decking to the roof rafter beams. Two layers of foam will fill between the extensions and the last layer of foam will cover the extensions. Over the foam will be 5/8 Zip osb with taped seams. I will use archetectural shingles. My questions: 1) do I need to tape the poly-iso seams?  (I was going to fill any defects with can-foam. ) 2) Do I need to be concerned with screwing the rafter extensions through the OSB/decking to the main beams? 3) are there any details I should be considering?

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