We are installing a Zehnder in a home where all the internal comfotubing was run but the intake and exhaust penetrations were not made prior to finishing.  We’ll be cutting the penetrations (from the interior to the exterior) in the ICF foundation wall but I’m curious about the best approach for air sealing and flashing the penetration where the stucco has already been applied to the exterior.  It will probably be difficult to remove the stucco cleanly around the penetration to apply a gasket to the exterior.  Would it be sufficient to spray foam the pipe in place and then use a bead of silicone at the grille connection and then use a roflex gasket and tape on the interior?  Or am I better off removing a larger patch of stucco and applying the gasket and tape on the exterior.

Cheers