I am new to your site and am in need of assistance. I have gutted a bathroom to the studs. On the exterior wall of the bath, there is a section where the external sheathing has failed. I can see through to the back of the brick exterior. I have used bleach to remove the mold and applied a product to prevent future mold growth. Now I need to repair the hole and prevent future water intrusion. I know I cannot just use foam to fill the hole because I need the air gap. I was thinking of afixing a water resistant sheathing type material to the interior of the external sheathing and siliconing around the hole as I install it. Is this a realistic fix, or is there a better way? Would an insulation board be appropriate for this job? I plan on staying in the house, so don't want to redo the bath in a few years due to water damage. Thanks for your help.