Exterior Wall in Bathroom
When I pulled the drywall down on the bathroom shower wall, I see that the insulation is black in a few areas and the sheathing has what looks like air movement marks. Where the problem is worst is where there's a gap between the sheathing and the stud. The sheathing is bowed out for about 12".
From outside to inside the wall in this area is> aluminum siding, membrane, (not sure of the type) sheathing, insulation, poly, drywall, tile.
How would I prevent this from happening again?