I’m considering including a service cavity wall on the interior side of the exterior walls in my house construction plans.  I’m doing this to create a more durable interior air barrier that will not be compromised by electrical boxes or other drywall penetrations.  Seems easier than the ADA method.  However, I’m concerned that I might be compromising the wall’s ability to dry to the interior as is necessary with exterior rigid foam, which I plan to include.  I’m in far northwest Arkansas, on the southern end of climate zone 4A, mixed humid.

From exterior to interior, the wall assembly will consist of siding, rainscreen furring, 1-1.5″ rigid foam (depending on what’s available reclaimed), housewrap, 0.5″ plywood – taped/caulked, 2×6 studs with mineral wool batts, OSB (for the air barrier, taped/caulked), 2×3 studs for uninsulated service cavity, and then drywall with latex paint (I know to avoid polyethylene and vinyl wallpaper).  

Based on permeance numbers online, I calculated the combined permeance of everything on the interior side of the plywood sheathing (my other air barrier) and came up with ~1.5 perms (I’m not a building scientist, so this could be way off).  

Am I asking for moisture problems with the multiple interior layers (OSB and drywall)?  I prefer OSB over smart vapor barrier because it is more durable, but would you recommend a smart barrier over OSB?  Would I need to include some kind of ventilation to the interior for the service cavity through the drywall?  If so, how?

Thanks for your comments!