The materials used to build a house are many, and they vary depending on where in the world one lives. Climate conditions, available resources, and traditional design all influence construction decisions. As a result, dwellings made from packed snow (igloos) and from reeds and grasses (thatched huts) are not only common in some parts of the world but also appropriate.
Building materials themselves are often made of other components known as "raw"materials. Common building bricks, widely used for house exteriors in North America and Europe, are made from a mixture of clay, sand, and other natural minerals. Water is added to the mix, and the soft mass is then shaped to a specific size in a mold and baked in a kiln until the material hardens and assumes its characteristic rectangular block shape and red or brown color. By contrast, adobe bricks, made by mixing clay or mud with straw and used since ancient times in Egypt, the Middle East, Central America, and elsewhere, are traditionally sun-dried.
Wood also undergoes several steps from raw material to finished lumber before it is used to build a house. After trees are cut -- more and more from planned tree plantations in order to preserve older, more ecologically rich forests -- logs are sawed into pieces of lumber at a mill. The lumber must then be thoroughly dried. Removing moisture from the millions of cells of which wood is made makes wood harder, stronger, stiffer, and lighter in weight. Because strength is such an important factor in building structures, wood is inspected for certain defects. Knots, decay, and warping all reduce strength and durability. A builder chooses pieces of lumber that are the right dimensions for the part of the house under construction -- long planks and beams for the frame, flat boards for the roof, shingles for siding.
