Iban settlements are still predominantly in the form of longhouses. During the time when headhunting was endemic, the longhouse provided a sound strategy of defense. It continues to be a ritual unit, and all residents share responsibility for the health of the community. A longhouse is an attenuated structure of attached family units, each unit built by a separate family. The selection of different building materials and the uneven skills of Iban men who build their own houses are apparent in the appearance of family units, some with floors of split bamboo, others with planed and highly polished hardwood floors. The average width of a family unit is 3.5 meters, but the depth, that is, the distance from front to back, varies widely. A longhouse may include as few as 4 families with 25 residents in a structure less than 15 meters long, or as many as 80 families with 500 residents in a house about 300 meters long. Access to a longhouse is by a notched-log ladder or stairs. At the top of the ladder is an uncovered porch ( tanju ) on which clothing, rice, and other produce may be dried. Inside the outer wall is a covered veranda ( ruai ), which is the thoroughfare for traffic within the house, where women and old men sit during the daytime weaving or carving, and where families gather in the evening to recount the day's events or to listen to folklore told by storytellers. Beyond the inner wall is the family apartment ( bilik ), where the family cooks and eats its meals, stores its heirlooms, and sleeps. Above the bilik and extending halfway over the ruai is a loft ( sadau ), where the family's rice is stored in a large bark bin and where unmarried girls sleep. The longhouse is constructed with its front to the water supply and preferably facing east. The core of each longhouse community is a group of siblings or their descendants. Through interethnic marriages, members of other societies may become part of Iban settlements and are assimilated as "Iban" in a generation or two. Until the past quarter-century, all Iban lived in or were related to longhouse settlements. Life in the longhouse was considered "normal," and those few people who lived in single-family dwellings apart from the longhouse were thought to be possessed by an evil spirit. Within the past 25 years, through a process of social and economic differentiation, many affluent Iban have built single-family houses. In the towns to which Iban are moving, they live scattered among Chinese and Malays in squatters' communities.