WALL

structural element used to divide or enclose, and, in building construction, to form the periphery of a room or a building. In traditional masonry construction, walls supported the weight of floors and roofs, but modern steel and reinforced concrete frames, as well as heavy timber and other skeletal structures, require exterior walls only for shelter and sometimes dispense with them on the ground floor to permit easier access. The traditional load-bearing wall of masonry is of a thickness proportional to the forces it has to resist: its own weight, the dead load of floors and roofs, and the live load of people, as well as the lateral forces of arches, vaults, and wind. Such walls are often thicker toward the base, where maximum loading accumulates. They can be thickened along their entire length or only at particular points where the force is concentrated; the latter method is called buttressing. Doors and windows weaken a wall and divert the forces above them to the parts on either side, which must be thickened in proportion to the width of the opening. The number of openings that can be used depends on the strength of the masonry and the stresses in the wall. Usually windows must be placed one above the other in multistory buildings to leave uninterrupted vertical wall masses to transfer loads directly to the ground. Positioning of walls depends on the type of support given floors and roofs. The usual beam supports must be jointed to walls at both ends, and their maximum length establishes the distance between bearing walls. All types of floors and roofs except the dome are most easily supported on straight, parallel walls. Nonbearing walls, used where loads are carried by girders, beams, or other members, are called curtain walls; they are attached to the frame members. Any durable, weather-resisting material-glass, plastic, metal alloy, or wood-may be used, since nonbearing walls are freed from the limitations of structural requirements.