American cockroaches will move indoors when they experience a food shortage or a significant change in the climate. In general, American cockroaches prefer warm, moist and dark environments with temperatures between 70-80 degrees Fahrenheit. They often enter structures by being brought in on human belongings, coming up from the sewer system via drains or occasional mass migration from other structures, dumps, etc., during warm weather.
American cockroaches are especially common in larger commercial buildings such as restaurants, bakeries, grocery stores, food processing plants, hospitals, etc., where they usually infest food storage and food preparation areas, boiler rooms, steam tunnels and basements.