I’m building a 12’x12’x12 shed with a 12/12 pitch roof out of rough cut lumber in zone 5-6. It’s a balloon framed  shell with cathedral ceilings and a loft at a height of 8′ that is ~8’x8′. The rafters are 2″x8″x10′ which provide a 1′ overhang on all sides. I strapped the whole outside to prevent racking and then added a Tyvek WRB with all holes and seams taped.  I’m  still waiting for the exterior 3″ comfort board 80 to arrive. The roof has 4″ of foam encased in a 2″x4″ perimeter frame and will have 8″ of roxul insulation for an effective R value of ~ 45. I’m making the roof assembly a non vented roofing assembly…

My question is can i run the WRB up the load bearing wall and continue it  down the rafter, out the end of the eave and up the fascia to the roof to make it an air tight seal. If I don’t do this I don’t see any way to make it air tight  except on the inside of the building with a smart vapor barrier. My thoughts on this is that its better to have insulation inside and an air barrier on the outside  that is sealed just like putting on a wool sweater and then a light rain jacket as compared to the other way around…  

Any problems with doing this as my roof assembly is sealed and I plan on insulating my eves as well?

Thanks,

Greg