Max Kuo, the cofounder of AllThatIsSolid, a practice based in both Kuala Lumpur and L.A., wanted to create a well-designed setting that would accommodate a mix of households sharing a single-family lot. With a budget of roughly $538,000, the team converted the original back house and attached garage into a white-gabled duplex with a 900-square-foot, two-bedroom apartment on the ground level and a 700-square-foot studio upstairs.