Question: Will installing closed cell spray foam over the ventilation for a basement French drain significantly affect the sump pump system's ability to remove water from the basement?
Background: I recently had a sump pump installed. The installers left an air gap for weep holes in my cinder block foundation with some thick plastic-type sheeting over it similar to what is shown in this picture. At the end of the job, the installers told me to make sure that if I painted the walls, that I should make sure to go along the top of the plastic sheeting with an exacto knife to allow air to flow down into the French drain and prevent a vacuum.
I would now like to use closed cell foam to insulate and provide a vapor barrier on my basement walls as part of finishing the basement. This puts me between a rock and a hard place on advice for using closed cell foam:
If I use closed cell foam without cutting along the top of the plastic sheeting of the French drain, I will be violating the advice of the installer and significantly impeding the transmission of air into the French drain.
If I use closed cell foam and put a cut along the top of the plastic sheeting of the French drain, then I will satisfy the French drain installer's advice while reducing the foam's effectiveness as a vapor barrier and defeating one of the purposes of using it.