Houses are where humans typically live. They exist to protect people from the elements, specifically temperature control, blocking precipitation, and keeping out wild animals. They also allow for a degree of privacy. They often include areas or rooms for cooking, bathing, hygiene/sanitation and sleeping. A house or shelter may contain only some, or even none of these elements. Houses may be constructed from a variety of materials, including wood, earth, stone, and metal. In most contexts permanent buildings cost money to build. However, sometimes houses are built as a community service, such as with the organization Habitat for Humanity. In other contexts houses may be constructed using locally available resources or scavenged materials.