An accessory dwelling unit, usually just called an ADU, is a secondary housing unit on a single-family residential lot. These ADU’s can come in many types & forms but most cold-formed steel ADU’s are new construction detached units. The uses for these ADU’s range from renting out for extra income, using as office space, or housing a relative or friend. There are states and cities that are encouraging the building of ADU units, tax credits may be available depending on the rules of your municipality.