Ensure that the tops of all blocks angle inward Credit: Courtesy of W.W. Norton & Company
Miter the ends of the blocks for a tight fit Credit: Courtesy of W.W. Norton & Company
Cut a ramp in the blocks that continues at least halfway around the circle Credit: Courtesy of W.W. Norton & Company
Lines drawn along the slanting tops of all blocks should point to the center of the igloo Credit: Courtesy of W.W. Norton & Company
The igloo grows as equally sized blocks are added along the spiral ramp Credit: Courtesy of W.W. Norton & Company