It can take anywhere from six weeks to six months to build a 2,800-square-foot, two-story house in the United States, mostly because human beings do all the work. Within the next five years, chances are that 3-D printing (also known by the less catchy but more inclusive term additive manufacturing) will have become so advanced that we will be able to upload design specifications to a massive robot, press print, and watch as it spits out a concrete house in less than a day. Plenty of humans will be there, but just to ogle.