Hello,

Next month I'm going to be partially resheathing and residing an
exterior wall, so it will be open to the studs from the outside. The
wall currently has cotton batt insulation, and I understand batt
insulation can be leaky where it meets the framing. So I'm wondering
what I can do from the exterior to seal up the wall cavity better, and
I'm thinking foam. I'm considering a few options:

1) Discard the batts and foam the entire wall cavity. Probably too
expensive given my climate (Berkeley, CA).

2) Spray the perimeter of each batt to seal it to the framing. Will
this work?

3) Temporarily remove the batts and spray a thin layer of foam against
the wallboard. The interior was recently remodeled, so the
wallboard won't need replacing any time soon.

Which of these is the way to go? In some areas I won't be removing
the existing 1x4 plank sheathing, in which case option (3) isn't
available. The plank sheathing has wide gaps everywhere, so I
should still be able to access the wall cavity through it.

Thanks, Wayne