Questions about air sealing old 1×8 sheathing, housewrap, foam insulation
(zone 4c here)
I’m having a hard time finding much information about how to air seal old horizontal 1×8 board sheathing. House wrap seemed like the clear choice until I realized that you aren’t supposed to tape the bottom seam. That seems like a huge flaw. Perhaps I could instead air seal the sheathing, by using flashing tape on every single board seam. It would be tedious and more expensive, but it wouldn’t leave a huge gaping opening around the whole perimeter of the house. The house is rather small (simple 900sf single story), so the cost/labor wouldn’t be unbearable or anything. The house wrap would then just be the WRB, not the air barrier.
If I’m adding foil-faced polyiso foam over the housewrap, and the wall system is then expected to dry to the interior, what is the purpose of using permeable housewrap at all? Could poly sheeting be used, in principle? (I don’t see any reason to actually use it, just trying to understand)
A final, somewhat strange question: I’ve only seen inside of my wall once, where they opened it to install the mini split head. The cavity was empty (no insulation) and it appeared that there was asphalt felt underneath the sheathing — in other words, when I looked into the hole from inside the house, I saw a black surface. They cut the hole, and then the sheathing was visible in the cut hole. Does this present any problems? Is it OK to have the sheathing sandwiched between external rigid foam (and housewrap) on the outside, and asphalt felt on its inside face? If not, what are my options?