When asked to build housing for 100 families in Chile ten years ago, Alejandro Aravena looked to an unusual inspiration: the wisdom of favelas and slums. Rather than building a large building with small units, he built flexible half-homes that each family could expand on. It was a complex problem, but with a simple solution — one that he arrived at by working with the families themselves. With a chalkboard and beautiful images of his designs, Aravena walks us through three projects where clever rethinking led to beautiful design with great benefit.