Many inventions, in hindsight, feel more like discoveries. Think of the bicycle, or the steam engine, or glass—all simple and useful enough to be widely copied once they were known.
Another such invention, 3-D printing, is now scaling up. All over the world, an impressive diversity of people and organizations, ranging from startups and hobbyists to construction and engineering firms, are successfully prototyping 3-D-printed buildings.
The printer extrudes cement in much the same way a desktop 3-D printer extrudes plastic: A print head attached to a robotic arm moves around and around, depositing one layer at a time, until a structure grows up from nothing.
But the more you examine the basics—the way the technology could potentially save energy, materials and time—the more it starts to feel like an idea that just might work.