Q. When staying in an apartment with a non-religious roommate, does one need to tell him to throw out (or keep separately) his chametz during Pesach, or may one allow him to store his chametz in the shared refrigerator, such as on a separate shelf?
A. Horav Shlomo Miller’s Shlit’a opinion is that you should definite try to have your irreligious roommate observe at least inside the apartment you share the prohibitions of chometz, even if it means to compensate him with a gift.
If that is not possible, and yo need to stay in the apartment, try you best not to use the shared refrigerator, since some chometz particles may drop into your shelf.
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit’a