Hello! I wanted to start by thanking everyone for their contributions; I’ve learned a lot from you all.

I’m trying to figure out the best way to upgrade our insulation and air seal our leaky house from the inside, as we’re planning to open up most of the walls during the renovation. We’re in marine climate zone 4 (Seattle area).

Previously we opened up the wall (unrelated water pipe burst), and noticed that our exterior sheathing appears to be 2x6s with some significant air gaps between the boards. Our previous blower door test indicated 10.5 ACH, so we have a very leaky building. Air sealing is a big area I’d like to upgrade, along with insulation while the walls are open. I’m also concerned about vapor if we’re upgrading the air sealing, so picking a good vapor solution is important. 

I am considering an interior flash and batt as a way to air and vapor seal the outer walls from the inside(I know CCSF is not great for the environment, but not sure of a better way to air seal from the inside).

I am also considering mineral wool in existing 2×4 bays, adding a 1″ layer of polyiso to address thermal bridging, and taping for air sealing, then drywall over that. This is a less palatable option, as this will cause some alignment issues with the finished walls and custom framed windows in many areas of the house.

To further complicate matters, we have TnG car decking for our ceilings, which our energy audit showed air leakage in the grooves that are continuous from the interior side to the exterior soffit overhang.  

Looking for ideas for insulation, air sealing, and how to manage vapor if we’re able to tighten things up. 

Thank you in advance!