The problem of inadequate or nonexistent housing has reached crisis proportions globally. The world population passed 6.1 billion in 2001 and is expected to reach 7.9-10.9 billion by 2050, according to the United Nations (UN) Population Fund. This sheer volume alone exerts enormous pressure to improve existing housing and create new homes. As the global population grows, rural areas around the world are emptying and mega cities springing up, usually as unregulated districts circling an older, more organized core.