What are duplex house plans? Duplex house plans feature two units of living space - either side by side or stacked on top of each other. Different duplex plans often present different bedroom configurations. For instance, one duplex might sport a total of four bedrooms (two in each unit), while another duplex might boast a total of six bedrooms (three in each unit), and so on. Is a duplex considered multi-family? Yes, because more than one family can live comfortably in a duplex. In fact, if you think you might house aging family members down the road, a duplex plan might be your best bet, as this type of home allows you to keep loved ones close while still maintaining a good amount of much needed privacy.