Plywood Sheathing Outward Drying Potential
I have a post and beam house with site built insulation “panels” that are really just 2×6 walls, outside the posts, built as follows, from inside to out:
Sheetrock, airspace w/ electrical, 3″ closed cell spray foam, 1″ continuous styrofoam, 5/8″ plywood sheathing, Tyvek, cedar clapboards.
By the nature of these being outside the frame, it is hard now to access some of it.
Recently I noticed some wet sheathing (some rotting). That is being replaced now. With blower door testing, some air leaks (gaps) through the sheetrock (especially in areas hidden behind beams) have been found. I can caulk those and retest with blower door, that’s a good thing.
I’m trying to learn more about how wall components can dry, it seems the sheathing is the critical item in my walls that needs to dry (learning a lot on this site). I guess one good thing is that nothing is blocking air and moisture leaving the sheathing to outside except the tyvek and clapboards. I understand a rain screen would have been helpful, but its tricky to add one now.
I will seal every leak I can find, and maybe then some. But as added insurance, what would be the best thing I could do to make it less likely the sheathing will get soaked again, and not be able to dry?
Is this a case where maybe asphalt building paper would allow more drying than tyvek?
What would the result be of adding dense packed celulose be in the 2.5 inch air space/electrical area behind the sheetrock? (colder sheathing but less airflow?)
Add better ventilation with rainscreen or vinyl siding?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part