Front Yard, Trees, Grass, and Living Room Using a 3D printing robot to print the walls, roof and floor—PassivDom's 380-square-foot model can be printed in about eight hours. The rest of the home such as the windows, doors, plumbing, and electrical systems are then added by hand.  Photo 4 of 6 in This Zero-Energy Passive Mobile Prefab Was Partially 3D Printed