About 80% of undergraduates and 20% of graduate students live on campus. The majority of the graduate students on campus live in one of four graduate housing complexes on campus, while all on-campus undergraduates live in one of the 29 residence halls. Because of the religious affiliation of the university, all residence halls are single-sex, with 15 male dorms and 14 female dorms. The university maintains a visiting policy (known as parietal hours) for those students who live in dormitories, specifying times when members of the opposite sex are allowed to visit other students' dorm rooms; however, all residence halls have 24-hour social spaces for students regardless of gender. Many residence halls have at least one nun and/or priest as a resident. There are no traditional social fraternities or sororities at the university, but a majority of students live in the same residence hall for all four years. Some intramural sports are based on residence hall teams, where the university offers the only non-military academy program of full-contact intramural American football. At the end of the intramural season, the championship game is played on the field in Notre Dame Stadium.