Plastic Vapor Barrier with ZIP-R in Zone 6
My first question. Thanks in advance.
My husband and I are building a post-frame workshop in Zone 6. For our walls, we’re using 2×6 bookshelf girts, batt insulation, and ZIP-R (R-6) sheathing. For our roof (4:12 w/ 24′ span), we’re hanging batt insulation between 2×4 on-edge purlins and we’re sheathing with ZIP-R (R-9). Our attic is within the building envelope but not usable. Of course we want more roof insulation, so we’re considering blown-in cellulose atop the interior ceiling.
Two questions, please:
1) We’ll be living in this building for a couple years while we build our actual home. Should we attach plastic sheets to the inside of our walls and to the bottom of our trusses to prevent moisture from entering the walls/attic during the cooling season? We’re concerned that the ZIP-R might not be vapor permeable enough and that we might trap moisture in the walls/attic (should it ever happen to enter into those cavities)?
2) Do you foresee any issues (e.g. moisture) in the attic if we have insulation on top (purlins/sheathing) and bottom (atop the interior ceiling) of trusses? The trusses are 4:12 pitch with 24′ span, so only 4′ or so of height at ridge.
Thanks for your thoughts and guidance,
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