Substance-free ("sub-free") floors are floors designated as drug- and alcohol-free zones. Students choosing to live on these floors must sign contracts stating that they will not possess alcohol or illegal drugs, and that if they choose to use them at another location, that they will return to their rooms as quickly and quietly as possible so as not to appear visibly intoxicated. Sub-free floors are typically quieter than non-sub-free floors because they do not usually have as many large parties.
Minnesota state law and college policy explicitly prohibit possession and use of illegal drugs by any person, so all floors are supposed to be drug-free. Carleton's alcohol policy does allow for the possession of and use of alcohol by persons 21 years of age or older (as allowed by state law) at registered parties and in residence hall rooms. However, students living on substance-free floors are prohibited from possessing or using alcohol while on the floor even if they are of legal drinking age.
Some sub-free floors take their obligations more seriously than others, though often RAs turn a blind eye to minor violations of the substance-free contract. In addition to one floor of every dorm hall, Rice House is also designated sub-free. It is widely regarded as one of the nicer off-campus houses to live in because of several very spacious rooms.
In general, residents of sub-free floors maintain a less inebriated, although by no means less interesting, life than the rest of campus. As many a sub-free RA has said, "Sub-Free doesn't mean Sub-Fun". That said, some sub-free residents do choose to use alcohol or other drugs sometimes. To do so, they often leave the floor to go to another party. The Substance-Free Living Agreement does not prohibit residents of sub-free floors from using alcohol off of the floor, but they are obliged not to disturb other residents when they return.