Wind-driven air leaks through rim joists and walls
Why it happens here
The hills sit above the valley floor and take direct wind on the west side. That pressure pushes air through every gap in the rim joist, top plate, and sheathing. Fiberglass batts do not stop air movement, so the R-value never performs as rated.
Our approach
We air seal with closed-cell spray foam before installing any insulation. That stops the wind-driven infiltration at the source. We then verify with a blower door test so you can see the leakage reduction in numbers.