Eighteen-foot-long ribs run from top to bottom to form the treehouse's struts. The floor package runs into the ribs and creates a triangle, which negated the need for more structural support. During construction, Allen broke one of the long ribs but rather than throwing the material away, he repurposed it for the entryway.  Modern Treehouses by Aileen Kwun from The Most Popular Homes in Dwell: 61-80